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Blood Tests

A blood test is one of the most common tests healthcare providers use to monitor your overall health or help diagnose medical conditions. You may have a blood test as part of a routine physical examination or because you have certain symptoms.

Overview

What are blood tests?

Blood tests are common medical tests. You may have a blood test as part of a routine physical examination or because you have certain symptoms.

There are many different blood tests. Some tests focus on your blood cells and platelets. Some evaluate substances in your blood such as electrolytes, proteins and hormones. Others measure certain minerals in your blood.

Regardless of why you’re having a blood test, it’s important to remember that blood tests help healthcare providers diagnose health issues. But blood test results aren’t diagnoses. An abnormal blood test result may not mean you have a serious medical condition.

When would I need to have a blood test?

Your blood plays a big role in your overall health and contains a lot of information about what may be going on in your body. That’s one reason why blood tests are a common medical test. A healthcare provider may do a blood test because:

It’s time for your regular physical. During a checkup, your provider may order blood tests to check on your overall health. They may order a blood test that evaluates many parts of your blood, such as a complete blood count (CBC), basic metabolic panel (BMP) or a comprehensive metabolic panel.

Your provider recommends screening tests. Screening tests are done before you have any symptoms. They may recommend screening tests if you’re at risk of developing certain conditions, such as cancer. For example, if you’re at risk for developing coronary artery disease, your healthcare provider may order several blood tests to evaluate that risk.

You don’t feel well. If you have specific symptoms, your provider may order blood tests to determine what’s causing them. For example, if you have symptoms that may be signs you’re pregnant, your provider will do a pregnancy test. The blood test looks for a specific hormone your body only ever makes when you’re pregnant.

You have a medical condition that happens when certain genes change (mutate). Depending on your situation, your blood cells and platelets may show information about the specific changes. Understanding which genes changed may help your provider plan your treatment.

You’re receiving treatment for a medical condition. Your provider may use regular blood tests to see if treatment is working.

You may have inherited certain genetic mutations that cause medical conditions. Your provider may take blood samples for genetic analysis so you know if you’re at risk of developing a specific condition.

What do blood tests show?

In a broad sense, a blood test shows changes in your body. Blood test results don’t show a complete picture. Instead, they’re a kind of snapshot. After seeing that snapshot, your provider may do other blood tests to get a closer view. Here’s a glimpse of what your healthcare provider may see with blood tests:

The tests show if your blood is working as it should. For example, your red blood cells carry oxygen throughout your body. A blood test may show you have low red blood cell levels (anemia). If healthcare providers look at your cells under a microscope, they may see your red blood cells are larger than normal or shaped differently than normal red blood cells. These differences may be signs of blood disorders or blood cancers.

They show if you have normal levels of enzymes and electrolytes. Enzymes are proteins that help speed up the chemical reactions that build up and break down substances in your body. Electrolytes do several things, such as helping your body regulate chemical reactions and maintaining the balance between fluids inside and outside your cells.

What are the most common blood tests?

There are many different blood tests. Some tests — such as complete blood count tests, basic metabolic panels, complete metabolic panels and electrolyte panels — check on several different elements in your blood at the same time. Other blood tests look for very specific elements in your blood.

Complete Blood Count (CBC)

A complete blood count (CBC) is a blood test. It's used to look at overall health and find a wide range of conditions, including anemia, infection and leukemia.

A complete blood count test measures the following:

Red blood cell count (RBC), These deliver oxygen throughout your body. They also help carry carbon dioxide. If your RBC count is too low, you may have anemia or another condition.

White blood cell count (WBC), These help your body fight germs. If you have too many of them, it could be a sign of inflammation, infection, a medical reaction, or another health condition. If it’s low, you could be at a higher risk for infection. A medication, a viral infection, or a bone marrow disease could also cause a low count.

Hemoglobin, the oxygen-carrying protein in red blood cells

Hematocrit, This test tells how much of your blood is made up of red blood cells. A low score may be a sign that you don’t have enough iron, the mineral that helps your body make red blood cells. A high score could mean you’re dehydrated or have another condition.

Mean corpuscular volume (MCV). This is the average size of your red blood cells. If they’re bigger than usual, your MCV will be higher. That could happen if you have low Vitamin B12 or folate levels. If your red blood cells are smaller, you could have a type of anemia.

Platelet count, A platelet count that's lower than usual is known as thrombocytopenia. If it's higher than usual, it's known as thrombocytosis. Either can be a sign of a medical condition or a side effect from medicine. A platelet count that's outside the typical range will likely lead to more tests to diagnose the cause.

A complete blood count can show unusual increases or decreases in cell counts. Those changes might point to a medical condition that calls for more testing.

Basic Metabolic Panel (BMP)

A basic metabolic panel (BMP) measures several substances in your blood. Healthcare providers use BMPs to evaluate your overall health and screen for or monitor health issues.

A BMP may include a:

Blood glucose test: Normal range is 64 to 100 mg/dL (3.55 to 5.55 mmol/L) Glucose (blood sugar) is your body’s main source of energy. Elevated blood glucose (hyperglycemia) is often a sign of diabetes.

Calcium blood test: Normal range is 8.5 to 10.2 mg/dL (2.13 to 2.55 mmol/L) Calcium is one of the most important and common minerals in your body. Your body stores most of it in your bones, but you also need calcium in your blood. Blood calcium is essential for keeping your nerves, muscles and heart healthy.

Blood urea nitrogen (BUN) test: Normal range is 6 to 20 mg/dL (2.14 to 7.14 mmol/L) Measures the amount of urea, a waste product that passes through your kidneys. BUN tests show the amount of urea nitrogen in your kidneys.

Creatine kinase (CK) test: Normal range is 0.8 to 1.2 mg/dL (70.72 to 106.08 µmol/L) This is a waste product that comes from digesting dietary protein and the normal breakdown of muscle tissue. Your kidneys filter it and remove it from your blood.

Sodium levels: Normal range is 136 to 144 mEq/L (136 to 144 mmol/L) Most of your sodium comes from the food you eat. It’s critical in helping your cells maintain the right balance of fluid. Your kidneys help regulate your body’s sodium levels.

CO2 blood test: Normal range is 23 to 29 mmol/L Bicarbonate indicates the amount of carbon dioxide (CO2) in your blood. It helps maintain a healthy acid-base (pH) balance.

Serum potassium test: Normal range is 3.7 to 5.2 mEq/L (3.7 to 5.2 mmol/L) Measures potassium levels. Potassium supports your heart, nerve and muscle function and your metabolism.

Chloride blood test: Normal range is 96 to 106 mmol/L Checks on chloride, an electrolyte that helps keep your body fluids and acids balanced.

Globulin blood test: Measures how much of this protein your liver produces.

Comprehensive Metabolic Panel (CMP)

Comprehensive metabolic panels (CMP) include all the blood tests done as part of a basic metabolic panel (BMP).

Additional blood tests include:

Albumin blood test: Albumin is a protein in your blood plasma. This test checks on kidney and liver function.

Alanine transaminase (ALT): Healthcare providers use this test to assess liver health.

Alkaline phosphatase (ALP): High levels of this enzyme may indicate liver disease or certain bone disorders.

Ammonia levels: Blood tests will show the amount of ammonia in your blood. High ammonia levels may be a sign of liver and kidney damage.

Bilirubin blood test: Bilirubin is a substance in your liver’s bile. Too much bile in your blood may be a sign of liver issues.

Aspartate transferase(AST): this test measures the amount of the enzyme aspartate transferase in your blood. Providers use this test to assess liver health.

total protein: this is the total amount of protein in your blood. It includes albumin and globulins, which are mainly made in your liver.

Coagulation Panel

Clotting is what prevents excessive bleeding when you cut yourself. But the blood moving through your vessels shouldn’t clot. If such clots form, they can travel through your bloodstream to your heart, lungs, or brain. This can cause a heart attack, stroke, or even death. Coagulation tests measure your blood’s ability to clot, and how long it takes to clot. Testing can help your doctor assess your risk of excessive bleeding or developing clots (thrombosis) somewhere in your blood vessels.

Results from a coagulation panel can be used to diagnose:

Pregnancy-related eclampsia

Hemophilia (excessive bleeding)

Cancer or cancer treatment

Autoimmune disorders

Vitamin K deficiency

Sepsis

Infections

Obesity (blood clots)

Liver function test

The liver function test checks your liver health by measuring different substances the liver produces. The test includes checking your:

Albumin: This is a protein made by your liver.

Total protein: This is the total amount of protein in your blood.

Alkaline phosphatase (ALP): This is an enzyme made by your liver.

Alanine transaminase (ALT): This is an enzyme made by your liver.

Aspartate aminotransferase (AST): This is an enzyme made by your liver.

Gamma-glutamyl transferase (GGT): This is an enzyme made by your liver.

Bilirubin: This is a waste product of your liver.

Lactate dehydrogenase (LDH): This is an enzyme released when cells are damaged.

Prothrombin time (PT): This is a protein that helps your blood clot.

If these levels are atypical, it could indicate liver disease or damage.

The tests look at alanine transaminase (ALT) and aspartate transaminase (AST) levels. These enzymes are mainly in the liver. When the liver is hurt or inflamed, their levels go up. This can mean different liver problems.

Condition	ALT Levels	AST Levels
Hepatitis	Elevated	Elevated
Cirrhosis	Mildly Elevated	Mildly Elevated
Fatty Liver Disease	Elevated	Normal to Mildly Elevated
Alcohol-related Liver Disease	Elevated	Elevated (Often Higher than ALT)

Kidney Function

Kidney function tests are key to checking your kidney health. They look at substances in your blood to see how well your kidneys work. They help figure out if your kidneys are filtering waste and keeping fluid balance right. Creatinine levels and the estimated glomerular filtration rate (eGFR) are important signs of renal function.

Creatinine and eGFR

Creatinine is a waste made by your muscles and filtered by your kidneys. High creatinine levels can mean your kidney function is not good or you might have kidney disease. The eGFR uses your creatinine levels, age, sex, and race to estimate kidney filtering. A low eGFR means your renal function is not as good.

Blood Urea Nitrogen (BUN)

Blood urea nitrogen (BUN) is another important kidney function marker. Urea is a waste from breaking down protein. Healthy kidneys remove urea from your blood. But, if your kidneys are not working right, BUN levels go up. High BUN, along with high creatinine and low eGFR, can mean your kidneys are not working well.

Your doctor will look at your test results and your health history. They consider your age, medical history, and any symptoms. Regular tests can catch kidney disease early. This helps keep your renal function good and prevents problems from a low glomerular filtration rate.

eGFR (mL/min/1.73 m²)	Kidney Function
90 or above	Normal
60-89	Mild decrease
30-59	Moderate decrease
15-29	Severe decrease
Less than 15	Kidney failure

C-reactive Protein (CRP) Test

A C-reactive protein (CRP) test measures the level of C-reactive protein in your blood. Your liver releases CRP into your bloodstream in response to inflammation. Healthcare providers use this test to help diagnose and monitor several different causes of inflammation, such as infections and certain autoimmune conditions.

Severe bacterial infections, such as sepsis.

Fungal infections.

Osteomyelitis (infection of your bone)

Pelvic inflammatory disease (PID)

Inflammatory bowel disease (IBD)

Autoimmune diseases, such as rheumatoid arthritis or lupus (systemic lupus erythematosus).

Some forms of arthritis

Lipid Panel

A lipid panel measures the amount of cholesterol and triglycerides (fats) in our blood. The two common types of cholesterol — HDL and LDL — can affect your health in several ways.

Total cholesterol, Total cholesterol is the total of all cholesterol types in the blood. It includes both “good” and “bad” cholesterol. High total cholesterol can mean a higher risk of heart disease. But, looking at HDL and LDL cholesterol is more accurate for cardiovascular risk.

Low-density lipoprotein (LDL) cholesterol, This is called the "bad" cholesterol. Too much of it in the blood causes the buildup of plaque in arteries. Plaque limits blood flow. Sometimes, plaque also breaks apart. That can lead to a heart attack or stroke.

High-density lipoprotein (HDL) cholesterol, This is called the "good" cholesterol. It helps carry away LDL cholesterol, the bad cholesterol. That keeps arteries open and blood flowing more freely.

Triglycerides, Triglycerides are a type of fat in the blood. When you eat, your body converts calories it doesn't need into triglycerides. Then triglycerides are stored in fat cells. High triglyceride levels are linked with many risk factors. These include being overweight, eating too many sweets or drinking too much alcohol. Smoking, being inactive or having diabetes also may raise the risk of high triglycerides.

Simple changes to your diet and lifestyle will go a long way in getting those lipid levels under control. Talk with your doctor about what you can do to stay heart-healthy.

DHEA-sulfate Serum Test

Healthcare providers use DHEAS tests to measure levels of a steroid hormone that your body converts into estrogen and androgens (testosterone). A high test result may indicate an adrenal tumor or polycystic ovary syndrome (PCOS), while a low test result may indicate Addison’s disease. You’ll need additional tests for an accurate diagnosis.

Normal DHEAS Levels by Age and Gender

DHEAS levels go down as you get older. They also differ between men and women. Here’s a table showing the typical DHEAS ranges for each age and gender:

Age (Years)	Male (μg/dL)	Female (μg/dL)
0-1	20-275	15-260
1-4	7-210	5-95
5-9	9-130	9-160
10-14	10-530	35-535
15-19	120-870	70-740
20-29	280-640	65-380
30-39	120-520	45-270
40-49	95-530	32-240
50-59	70-310	26-200
60-69	42-290	13-130
70+	28-175	17-90

Enzyme Markers

An enzyme marker is a blood test to measure enzymes, proteins in your blood that can indicate tissue damage or disease. Elevated cardiac enzymes after a heart attack are a sign of serious heart damage. High levels of CPK isoenzymes may indicate a muscle disease, while elevated liver enzymes suggest liver damage.

Liver Function Enzymes: AST, ALT, ALP, and GGT

Liver tests are key to checking liver health. The main liver enzymes tested are:

Enzyme	Full Name	Normal Range	Elevated Levels May Indicate
AST	Aspartate Aminotransferase	5-40 U/L	Liver damage, hepatitis, cirrhosis
ALT	Alanine Aminotransferase	7-56 U/L	Liver damage, hepatitis, fatty liver disease
ALP	Alkaline Phosphatase	20-140 U/L	Liver disease, bone disorders, bile duct obstruction
GGT	Gamma-Glutamyl Transferase	0-30 U/L	Liver disease, alcohol abuse, bile duct disorders

Cardiac Enzymes: Troponins, CK-MB, and Myoglobin

Heart enzymes are vital for diagnosing heart problems, like heart attacks. The main heart enzymes are:

Troponins (I and T): Highly specific markers for myocardial damage

CK-MB (Creatine Kinase-MB): Indicates damage to heart muscle cells

Myoglobin: An early marker of myocardial injury

Pancreatic Enzymes: Amylase and Lipase

Pancreatic enzyme markers help diagnose pancreas problems, like acute pancreatitis. The two main pancreatic enzymes tested are:

Amylase: Elevated levels suggest pancreatic inflammation or injury

Lipase: More specific to the pancreas and often used to confirm pancreatitis

By looking at these enzyme levels, doctors can understand organ health. This helps them give the best care to their patients.

Thyroid Panel

A little organ that sits at the bottom of your brain, called the pituitary gland, produces a hormone that controls your thyroid. Higher test results may indicate hypothyroidism, a condition that happens as a result of your thyroid not making enough hormones. Lower test results may suggest that you have hyperthyroidism, a condition where your thyroid is producing too many hormones.

Triiodothyronine (T3): This test measures your body’s levels of T3, the other main thyroid hormone. If your doctor suspects that you might have hyperthyroidism but your T4 levels are normal, an elevated T3 level can help confirm the diagnosis.

Thyroxine (T4): Thyroxine (T4) is one of two hormones produced by the thyroid gland. It is an inactive thyroid hormone that freely circulates in the bloodstream, ready to be converted to the active form called T3. There are two types of T4: bound T4 (which is attached to proteins that prevent it from entering tissues) and free T4 (which is not attached to proteins and can enter tissues freely).

Thyroid-stimulating hormone (TSH): Thyroid-stimulating hormone (TSH) is produced by the pituitary gland situated at the base of the brain. It acts as a chemical messenger, telling the thyroid gland when to start producing thyroid hormones. When thyroid hormone levels are low, more TSH is produced to stimulate production. When levels are normal, the pituitary gland stops producing TSH. The TSH test measures how much or how little TSH there is in the bloodstream.

Thyroid antibody test: This test measures the levels of thyroid antibodies in your system, which may be elevated if your immune system is attacking your thyroid. The thyroid antibody test can help your doctor determine whether you have an autoimmune disorder like Graves’ disease or Hashimoto’s disease.

Many medications can help control abnormal TSH levels. Your doctor will work with you to balance out those hormones and restore your well-being.

Bone Marrow Biopsy

A bone marrow biopsy is a key medical test in hematology and oncology. It helps doctors find and track blood disorders and cancers. This is done by taking a sample of bone marrow tissue for analysis. It’s vital for those with blood issues or cancer treatments.

Bone marrow is soft tissue inside bones that makes blood cells. It’s essential for producing red and white blood cells, and platelets. A biopsy can show if bone marrow is working right. It might even decide if a stem cell transplant is needed, which can save lives.

Understanding a bone marrow biopsy is key. It’s important to know what it is, why it’s done, and how it affects your health. We’ll look into this important test, its uses, the process, and how it helps in treatment choices.

There are two types of procedures used to collect bone marrow samples for testing:

Differences Between Bone Marrow Biopsy and Aspiration

A bone marrow biopsy and aspiration are different, even though they’re often done together:

Bone Marrow Biopsy	Bone Marrow Aspiration
Removes a small, solid piece of bone marrow tissue	Withdraws liquid bone marrow through a needle
Provides information about bone marrow structure and cellularity	Provides information about cell morphology and maturation
Allows for evaluation of bone marrow fibrosis and architecture	Enables cytogenetic and molecular testing of bone marrow cells

Both tests are vital for understanding the bone marrow’s health. Doctors usually do them together. This way, they get a full picture of the bone marrow’s condition.

How Does Your Blood Type Impact Overall Health?

Your blood type is one of the things that can be measured with a blood test. Blood type is designated by two types of markers—the ABO type and the Rh type. A blood typing test detects the presence or absence of these markers. The plus sign indicates Rh markers, while the minus sign indicates Rh-negative.

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The Eight Main Blood Types
A+	A-
B+	B-
AB+	AB-
O+	O-

All these blood types are perfectly healthy. The significance of these blood types is that when you need a blood transfusion the blood given to you must be carefully matched to your type to avoid causing an immune reaction, which can be deadly.

Before transfusion, the recipient should be typed and their blood tested against the donor blood units (called a crossmatching test).

In general, donor blood that has A, B, or Rh+ markers can only be given to people with those same markers. Anyone can receive O- donor blood. However, outside of emergencies, it's preferred that type-specific, crossmatched blood be given.

Check out this page for a better break down of Blood Types

What blood tests diagnose specific conditions?

While the various blood and electrolyte panel tests provide a lot of information, there are disease-specific blood tests that help providers diagnose and treat specific conditions.

Allergies

An allergy blood test checks your blood for increased levels of immunoglobulin E (IgE) antibodies. The test can help detect allergies to foods, pets, pollen or other irritating substances.

Autoimmune diseases

Autoimmune diseases happen when your immune system accidentally attacks your body instead of protecting it from intruders like viruses, parasites and cancer. Your provider may order the following blood tests:

Antinuclear antibody test: Antinuclear antibodies (ANA) are antibodies that mistakenly attack your immune system. Large amounts of ANA in your blood may be a sign of certain autoimmune disorders.

CE complement blood test: Providers may use this test to diagnose and monitor autoimmune disorders like rheumatoid arthritis or lupus.

C-reactive protein (CRP) test: Your liver makes and releases this protein. High C-reactive protein levels may be a sign of inflammatory conditions, including some autoimmune diseases.

Erythrocyte sedimentation rate (ESR): ESR tests help detect inflammation.

Peripheral blood smear (PBS): This is a technique healthcare providers use to examine your red and white blood cells and your platelets under a microscope.

Cancer/Noncancerous blood disorders

Healthcare providers may use several different tests to diagnose and treat cancer, blood cancer and noncancerous blood disorders.

Cancer blood tests

Blood tests for cancer fall into four basic categories — complete blood count, tumor markers, blood protein testing and circulating tumor tests. CBC, tumor markers and circulating tumor tests may help detect some solid tumors. Blood in your poop (stool) or pee (urine) may also be a sign of cancer.

Complete blood count (CBC)

A CBC measures red and white blood cell and platelet levels. Abnormally high or low blood cell or platelet levels may be a sign of some types of cancer.

Tumor markers

Tumor markers are substances made by cancerous cells or your body’s normal cells in response to cancer. Tumor marker blood tests include:

Alpha-fetoprotein (AFP) for liver cancer.

CA-125 blood test for ovarian cancer.

Calcitonin for thyroid cancer.

Cancer antigens 15-3 and 27-29 for breast cancer.

Carcinoembryonic antigen (CEA) for a range of cancers.

Human chorionic gonadotropin (HCG) for testicular cancer and ovarian cancer.

Prostate-specific antigen (PSA) for prostate cancer.

Circulating tumor test

The circulating tumor test is a relatively new blood test for cancer. This test looks for cancerous cells that have broken away from a tumor and into your bloodstream. Currently, it can help monitor certain types of cancer, such as breast, prostate and colorectal cancers. Scientists are still developing the technology.

Other blood tests

Healthcare providers may use the same tests to diagnose blood cancer or noncancerous blood disorders:

D-dimer test: Healthcare providers use this test to diagnose blood clotting disorders.

Fibrinogen test: Fibrinogen is a protein that helps with blood clotting.

Kappa or Lambda free light chain: This test detects high protein levels in your blood plasma. Healthcare providers may use this test to diagnose amyloidosis, which is a noncancerous blood disorder, or to diagnose blood cancers such as multiple myeloma.

Prothrombin time test (PTT): Healthcare providers may use this test to diagnose blood clotting disorders.

Reticulocyte count: This test checks to see if your bone marrow is producing enough healthy red blood cells.

Some blood tests don’t involve providing blood samples, such as:

Fecal occult blood test (FOBT): FOBTs screen for colorectal cancer by looking for blood in your stool.

Urinalysis: Healthcare providers may use this test to detect blood cells in your urine.

Endocrine system disorders

Your endocrine system is made of organs called glands. Glands produce hormones. Healthcare providers may use blood tests to diagnosis conditions affecting parts of your endocrine system. Common blood tests include:

Blood glucose test: This test measures your blood glucose level. It’s used to diagnose diabetes. Another diabetes blood test is A1C, which measures blood glucose over time.

Thyroid stimulating hormone test (TSH): There are several blood tests to diagnose thyroid disorders.

Pancreas blood tests: Your pancreas produces enzymes. These tests check lipase and amylase levels.

Heart disease

Some blood tests evaluate your risk of developing heart disease:

Cardiac blood tests: Your healthcare provider may order these tests if you’re at risk of having a heart attack or developing heart disease.

Arterial blood gas (ABG) test: This test measures oxygen levels and carbon dioxide levels, among other things. Healthcare providers may do this test to diagnose acute heart failure and cardiac arrest.

Specialized blood tests

Your healthcare provider may recommend specialized blood tests, including:

Ammonia levels: Blood tests will show the amount of ammonia in your blood. High ammonia levels may be a sign of liver and kidney damage.

Blood alcohol content (BAC): This test measures the amount of alcohol in your system.

Ferritin: You may have a ferritin test if your CBC tests show you don’t have enough iron.

When should I have a blood test?

That depends on your situation and your overall health. Most healthcare providers recommend annual physical examinations that may include a complete blood count test. In general, providers recommend tests based on what they know about you. For example, they may recommend regular blood glucose tests if you have overweight (a Body Mass Index or BMI over 25) or obesity (a BMI greater than 30).

Test Details

What should I do to prepare for my blood test?

That depends on the kind of test you’re having. For example, some blood tests require you to fast for several hours before the test. You may be asked not to drink any liquids apart from a few sips of water. Most blood tests don’t require fasting, but it’s a good idea to ask your healthcare provider what to avoid before your blood test. Other steps may include:

If you don’t need to fast before your blood test and you’re able to drink water, try to drink as much as you can before your test. Being well-hydrated may make it easier for healthcare providers to obtain blood.

Use moisturizer on your arms. It may make it easier for your provider to insert the needle and obtain blood.

Boost your blood pressure right before your blood test by doing some gentle exercise while waiting to be called in for your test.

What happens during blood tests?

Phlebotomists — healthcare providers with special training in drawing blood — do blood tests. During the blood test process:

You’ll sit in a chair with an armrest where you can stretch your arm out in front of you.

If you’re wearing a long-sleeve shirt, you’ll roll up your sleeve past your elbow.

The phlebotomist will wipe an antiseptic liquid in the bend of your arm (on the other side of your elbow) and put an elastic band around your arm (above your elbow).

They may ask you to make a fist to encourage blood flow.

They’ll insert a needle into your arm. This typically happens very quickly. You may feel the needle go into your skin. This is called venipuncture.

The blood flows into a tube that’s sealed and sent to a lab for analysis. The phlebotomist may need to take several samples of your blood, depending on the blood tests your healthcare provider ordered.

Once the phlebotomist has obtained enough blood, they’ll remove the stretchy band that’s strapped around your arm and removes the needle.

Then, they’ll put a bandage on the area where the needle went into your skin.

Are there different ways to do blood tests?

All blood tests involve obtaining blood samples. Venipuncture (from a vein) is the most common procedure.

Other procedures are:

Finger stick: Your provider pricks one of your fingers with a needle to collect a tiny amount of blood. The blood sample is saved on a special strip of paper that’s sent to a lab for analysis.

Heel stick: All babies born in the U.S. have blood tests by pricking their heel with a needle to obtain a blood sample.

Arterial blood gas test: In this test, providers take blood from one of your arteries instead of a vein.

How much blood is taken during blood tests?

That depends on the kind of blood test. On average, a complete blood count (CBC) test may take as much as 30 milliliters (mL) of blood. It may sound like a lot of blood, particularly if you’re watching your blood flow into several sample tubes. But it’s not — the average adult has 4,500 to 5,700 milliliters of blood in their body.

Do blood tests hurt?

They can, depending on the kind of blood test you have. It’s important to remember that phlebotomists receive training on how to obtain blood samples quickly and without causing pain.

That said, tests that take blood from an artery tend to hurt more than tests that take blood from a vein. And with venipuncture, taking blood from a vein may hurt a bit if the phlebotomist has trouble inserting the needle into your vein. Let your phlebotomist know if you have any discomfort. They’ll try different ways to obtain samples of your blood.

I’m always anxious about having blood tests. What can I do to relax?

Many people feel anxious about blood tests. Some ways to cope include:

Understanding why you’re having specific blood tests.

Taking deep breaths as the needle goes into your arm.

Looking away so you don’t see the needle enter your arm.

Finding a way to distract your attention, such as silently counting to 10.

What happens after my blood test?

Your provider will put a bandage on the spot where the needle went in. Depending on the blood test, they may recommend you rest for a minute or so before standing up and leaving.

Results and Follow-Up

When will I know my test results?

That depends on the blood test and your provider’s preferences. Your provider likely will explain how you’ll receive results. Some blood test results are available within a few hours. Others, like genetic test results, typically take longer.

Some healthcare organizations offer online access to test results. But your provider may prefer to discuss your results in a telephone conversation or in person.

My healthcare provider wants to talk to me about my test results. Does that mean something’s wrong?

Not necessarily. If your tests were part of your routine medical checkup, your healthcare provider may want to review results with you. They may have recommendations about ways you can improve your health. If you’ve received treatment for a medical condition, your provider may want to discuss your test results in detail and put the results in context.

FAQ's

Q: What is the purpose of blood tests?

A: Blood tests help check your health, find diseases, and see how treatments work. They look at different parts of your blood to understand your body’s health.
Q: How should I prepare for a blood test?

A: Before a blood test, you might need to fast for 8-12 hours. Avoid some medicines and stay hydrated. Your doctor will tell you what to do based on your test.
Q: What happens during a blood draw?

A: A phlebotomist will clean the area and put a needle in your vein for blood. You might feel a pinch, but it’s quick and not very painful.
Q: What is a complete blood count (CBC)?

A: A CBC checks your red and white blood cells and platelets. It helps find issues like anemia, infections, and blood problems.
Q: What does a lipid panel measure?

A: A lipid panel looks at your cholesterol and triglycerides. It shows your risk for heart disease and helps decide treatment.
Q: Why are liver function tests performed?

A: Liver function tests check your liver health by looking at certain enzymes and proteins. They can spot liver damage or diseases like hepatitis.
Q: What do blood tests for kidney function assess?

A: Kidney function tests, like creatinine and eGFR, check how well your kidneys work. They help find and track kidney problems.
Q: How are blood test results interpreted?

A: Results are compared to normal values, which can change based on age, gender, and lab methods. Abnormal results mean you might need more tests or treatment.
Q: What should I do if my blood test results are abnormal?

A: If your results are off, talk to your doctor right away. They’ll explain what it means and what to do next, like more tests or changes in your routine.

One Final Note..

It’s probably fair to say blood tests are last on most people’s list of fun things to do. But blood tests are an essential tool healthcare providers use to monitor your overall health or diagnose medical conditions. You may have a blood test as part of a routine physical examination or because you have certain symptoms.

Regardless of why you’re having a blood test, it’s important to remember that while blood tests help providers diagnose health issues, they aren’t diagnoses. An abnormal blood test result may not mean you have a serious medical condition. If your healthcare provider recommends blood tests, they’ll be glad to explain why they recommend the test and what the test may show.

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Most recent revision June 30, 2025 08:08:42 PM

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