Blood tests can be used to help a doctor identify a variety of health conditions, including vitamin deficiencies, organ failure, HIV, cancer, diabetes, and more.
Regular blood testing is one of the most important ways to keep track of your overall physical well-being. Getting tested at routine intervals can allow you to see the way your body changes over time and empower you to make informed decisions about your health.
What does a blood test show?
Some blood tests can help your doctor determine how different organs in your body are working. Examples of organs whose malfunctions can be visible in a blood test
Your doctor can also use blood tests to search for markers of diseases and health conditions such as:
- coronary heart disease
Even if a person does not have heart disease, a blood test can show whether they may be at risk of developing the condition.
Other blood tests can indicate whether the medications you’re taking are working properly, or assess how well your blood is clotting.
Let’s take a closer look at some common blood tests.
1. Complete blood count
A routine complete blood count (CBC) checks for levels of 10 different components of every major cell in your blood: white blood cells, red blood cells, and platelets.
Important components this test measures include red blood cell count, hemoglobin, and hematocrit.
|red blood cells (cells responsible for carrying oxygen throughout the body)||male: 4.3–5.9 million/mm3; female: 3.5–5.5 million/mm3|
|white blood cells (immune system cells in the blood)||4,500–11,000/mm3|
|platelets (the substances that control the clotting of the blood)||150,000–400,000/mm3|
|hemoglobin (protein within the red blood cells that carries oxygen to organs and tissues, and carbon dioxide back to the lungs)||male: 13.5–17.5 grams/deciliter (g/dL); female: 12.0–16.0 g/dL|
|hematocrit (percentage of blood made of red blood cells)||male: 41–53%; female: 36–46%|
Abnormal levels of these components may
- nutritional deficiencies, such as vitamin B6 or B12
- anemia (iron deficiency)
- clotting problems
- blood cancer
- immune system disorders
Based on your results, your doctor will order follow-up tests to confirm abnormal levels and a possible diagnosis.
2. Basic metabolic panel
A basic metabolic panel (BMP) usually checks for levels of eight compounds in the blood:
- blood urea nitrogen (BUN)
This test may require you to fast for at least 8 hours before your blood is drawn, depending on the instructions of your doctor and what the test is measuring.
See our chart for normal results.
Abnormal results may indicate:
- kidney disease
- hormone imbalances
Your doctor will perform follow-up tests to confirm a diagnosis.
3. Comprehensive metabolic panel
A comprehensive metabolic panel (CMP) includes all the measurements of a BMP as well as additional proteins and substances related to liver function, such as:
- total protein
- alkaline phosphatase (ALP), an enzyme mostly found in the bones and liver that’s involved in several bodily processes
- alanine aminotransferase (ALT), an enzyme found in the liver
- aspartate aminotransferase (AST), an enzyme found in the liver and other tissues within the body
- bilirubin, which is waste resulting from the breakdown of red blood cells that the liver filters out
The same conclusions can be drawn from a CMP as from a BMP for the same substances that a BMP covers. Other abnormal levels can also indicate underlying conditions, such as:
|High levels||Low levels|
|ALP||• bile duct blockage|
• gallbladder inflammation
• Paget’s disease
|• bone metabolism disorders|
• heart surgery
• zinc deficiency
• liver cancer
• liver damage
• heart conditions
|bilirubin||• abnormal red blood cell destruction (hemolysis)|
• adverse medication reactions
• bile duct blockage
• Gilbert’s syndrome
|not a concern|
4. Lipid panel
This test checks levels of
- high-density lipoprotein (HDL), or “good” cholesterol
- low-density lipoprotein (LDL), or “bad” cholesterol
HDL is “good” because it removes harmful substances from your blood and helps the liver break them down into waste. LDL is “bad” because it can cause plaque to develop in your arteries, increasing your risk of heart disease.
You may need to fast for at least 8 hours before this test.
Here are the
|HDL||>60 mg/dL||male: <40 mg/dL; female: <50 mg/dL (low)|
|LDL||>160 mg/dL||<100 mg/dL (optimal)|
Normal levels can also vary by age.
5. Thyroid panel
A thyroid panel, or thyroid function test, checks how well your thyroid is producing and reacting to certain hormones, such as:
- Triiodothyronine (T3). Along with T4, this regulates your heart rate and body temperature.
- Thyroxine (T4). Along with T3, this regulates your metabolism and how you grow.
- Thyroid-stimulating hormone (TSH). This helps regulate the levels of hormones your thyroid releases.
Your thyroid is a tiny gland in your neck. It helps regulate bodily functions like your mood, energy level, and overall metabolism.
Here are normal results:
- T3: 80–180 nanograms per deciliter of blood (ng/dL)
- T4: 0.8–1.8 ng/dL in adults.
- TSH: 0.5–4 milli-international units per liter of blood (mIU/L)
Abnormal levels of these hormones can indicate numerous conditions, such as:
- low protein levels
- thyroid growth disorders
- abnormal levels of testosterone or estrogen
6. Cardiac biomarkers
Enzymes are proteins that help your body accomplish certain chemical processes, such as breaking down food and clotting blood. They’re used throughout your body for many vital functions.
Abnormal enzyme levels can indicate many conditions.
Common enzymes tested include:
- Creatine kinase (CK). This is an enzyme primarily located in the brain, heart, and skeletal muscle. When muscle damage happens, CK seeps into the blood in growing amounts.
- Creatine kinase-MB (CK-MB). These enzymes are found in your heart. They often increase in your blood after a heart attack or other heart injury.
- Troponin. This is a heart enzyme that can leak into your blood and results from heart injury.
Here are the normal ranges for the enzyme listed above:
- CK: 30–200 U/L
- CK-MB: 0–12 IU/L
- troponin: <1 ng/mL
7. Sexually transmitted infection tests
Many sexually transmitted infections (STIs) can be diagnosed using a blood sample. These tests are often combined with urine samples or swabs of infected tissue for more accurate diagnoses.
The following STIs can be diagnosed with blood tests:
Blood tests aren’t always accurate right after contracting an infection. For an HIV infection, for example, you may need to wait at least a month before a blood test can detect the virus.
8. Coagulation panel
Coagulation tests measure how well your blood clots and how long it takes for your blood to clot. Examples include the prothrombin time (PT) test and fibrinogen activity test.
Clotting is a crucial process that helps you stop bleeding after a cut or wound. But a clot in a vein or artery can be deadly since it can block blood flow to your brain, heart, or lungs. This can cause a heart attack or stroke.
Coagulation test results vary based on your health and any underlying conditions that may affect clotting.
Results from this test can be used to diagnose:
- excessive bleeding (hemophilia)
- liver conditions
- vitamin K deficiency
9. DHEA-sulfate serum test
The dehydroepiandrosterone (DHEA) hormone comes from your adrenal glands. This test measures whether it’s too high or too low.
In men, DHEA helps develop traits like body hair growth, so low levels are considered abnormal. In women, high levels can cause typically male traits, like excess body hair, to develop, so low levels are normal.
Low levels may be caused by:
- Addison’s disease
- adrenal dysfunction
High levels in men or women can result from:
- congenital adrenal hyperplasia
- benign or malignant tumor on the adrenal gland
- polycystic ovary syndrome (PCOS)
- ovarian tumor
10. C-reactive protein test
C-reactive protein (CRP) is made by your liver when tissues in your body are inflamed. High CRP levels indicate inflammation from a variety of causes, including:
- bacterial or viral infection
- autoimmune diseases, such Lupus or rheumatoid arthritis
- inflammation related to diabetes
- inflammation related to physical trauma or from habits like smoking
- <0.3 mg/dL: normal
- 0.3 to 1.0 mg/dL: minor elevation can be associated with a person’s sex, body mass index (BMI), or with conditions like depression or insomnia
- 1.0 to 10.0 mg/dL: moderate elevation usually caused by systemic inflammation, such as from an autoimmune disease, bronchitis, heart attack, or cancer
- >10.0 mg/dL: marked elevation typically caused by a serious bacterial or viral infection, major trauma, or systemic vasculitis
- >50.0 mg/dL: severe elevation usually caused by an acute bacterial infection
If you are showing concerning symptoms of any illness or long-term condition, visit your doctor for a checkup. They will conduct a physical examination and let you know what kinds of blood tests you’ll need to undergo.
If you want to request a routine blood test, the most common ones to consider are:
- complete blood count (CBC)
- basic metabolic panel
- thyroid panel
- nutrient tests for levels of vital nutrients, such as iron or B vitamins
Some other tests you may want include:
- enzyme markers if you’re at risk of cancer or other conditions like cirrhosis, stroke, or celiac disease
- sexually transmitted infection (STI) tests if you recently had sex without a barrier method or had sex with a new partner
If you need help finding a primary care doctor, then check out our FindCare tool here.
How often you should get a physical exam may depend on your age, according to guidelines from a variety of clinical organizations:
- ages 18 to 39: at least every 5 years
- ages 40 to 49: every 2 to 3 years
- ages 50 and older: every 1 to 2 years
Your doctor will decide whether you need any blood tests during your physical exam.
In general, recommendations
For people at a higher risk of heart disease, more frequent lipid testing may be necessary.
In addition, you should get a glucose blood test if your blood pressure is continuously above 135/80. People over age 50 should get a fecal occult blood test to screen for colorectal cancer annually.
But some doctors may still suggest routine blood work during your yearly physical exam, and in some cases, you may want to get additional testing. For example, when:
- You’re experiencing unusual, persistent symptoms. These could include anything from fatigue and abnormal weight gain to new pain.
- You want to optimize your health. Knowing levels of various blood components, such as HDL and LDL cholesterol, can allow you to tweak your diet or fitness plan to maximize healthy habits.
- You want to reduce your risk of disease or complications. Regular blood tests can catch the warning signs of almost any disease early. Many heart, lung, and kidney conditions can be diagnosed using blood tests.
Talk with your doctor first if you want to get certain tests done, or have them done more often than once a year.
Who orders my blood tests?
Your doctor typically orders blood tests for you during a physical, checkup, or an appointment intended to screen for a specific condition.
It’s possible to order your own blood tests without a doctor through laboratories like LabCorp and Quest Diagnostics, but health insurance may not cover these tests.
While such blood tests may more accessible and convenient, it may be harder to interpret the results without a medical professional.
Some blood testing facilities may also not give you accurate results.
One infamous case of this is Theranos. The California biotechnology firm shut down in 2018 when an investigation uncovered lies and fraud around the accuracy of its private blood-testing technology.
Currently, litigation is underway against the founder and chief executive of the company, Elizabeth Holmes.
Where can I get blood work done?
There are different locations that offer laboratory services that include blood work. Most hospitals contain a laboratory that you can visit to get tests done. Some laboratories will have walk-in options. Others may require an appointment.
Additional locations for blood testing may include:
- Private laboratories. Hospitals may use private labs to offload some testing from their own laboratories, or in cases when a specialized test is needed. Often, health insurance plans will require you to use a specific laboratory that is in their network for the test to be covered.
- Point-of care. This describes situations when you may need to get a blood test wherever you are receiving medical care. In routine scenarios, this typically
includesyour doctor’s office during an appointment. It can also include tests done inside an ambulance during transport, or at a cruise ship or military clinic, for example.
- Direct access testing. Also known as direct to consumer, it allows you to order your own test without a doctor’s referral. You get the test done at a laboratory specially set up for this purpose.
- Home testing. You
can getsome tests at a pharmacy and then do them at home. You may need a prescription for some tests, while others may be available over the counter. This can include things like blood glucose monitoring for people with diabetes, or the fecal occult blood test that screens for colorectal cancer. The Food and Drug Administration (FDA) must approve all home tests before they’re available for purchase.
Everything you eat and drink contains vitamins, proteins, and other nutrients that can cause the related levels in your blood to temporarily spike or drop.
Fasting for 8 to 12 hours helps ensure that blood test results are free from these variables, making your test results as accurate as possible.
Some common tests that may require fasting include:
- cholesterol tests
- blood sugar tests
- liver function tests
- kidney function tests
- basic metabolic panel
- glucose tests
Results may take anywhere from a few hours to a few days to become available. Here’s an overview of how long some common tests may take:
- complete blood count (CBC): 24 hours
- basic metabolic panel: 24 hours
- complete metabolic panel: 24 to 72 hours
- lipid panel: 24 hours
Timing can depend on the specific lab where you get tested, and how many tests you get done at once. If you order multiple tests, you may not get the complete results until all of the tests are completed.
Sometimes a lab will only release results to your doctor, who reviews them and then releases them to you.
While every laboratory or test-providing company may structure their result reports differently, they all must include the same components as mandated by federal legislation.
Some of that may be administrative content, such as the name of the person who did the blood test, the date the test was done, and the name of the doctor who ordered the test.
When it comes to understanding the results, you can look for the
- Quantitative test result. Results will be typically written out numerically in cases when the test measured the quantity of something. For example, if the test measured the amount of cholesterol in your blood.
- Abnormal markers. Often, a laboratory report will include some kind of marker to let you know if a result is outside the normal interval, and therefore abnormal. For example, you may see the letter H to indicate high, the letter L to indicate low, or the acronym WNL for “within normal limits.” You may see an asterisk and some additional comments in text if your results come out as highly abnormal. In this case, you’ll typically get a call from your doctor.
- Reference range. Every laboratory will have its own reference range for each type of test. Typically, this reference range will be written in your laboratory report next to the numerical value of your result so you are able to see where your result falls in the range.
A nurse or technician usually performs a blood test at a laboratory or in a doctor’s office. The procedure takes just a few minutes.
- Cleans the area on your arm where they’ll draw the blood from.
- Ties a rubber band to your upper arm to help make your veins more visible, and asks you to make a fist.
- Puts a needle attached to a tube gently into a vein to draw blood.
- Removes the needle from the skin and takes the rubber band off your arm when the collection is complete.
- Covers the drawing site with a bandage or clean cotton and medical tape.
The risks of routine blood tests are very low but can include:
- slight pain or discomfort when the needle goes in
- fainting from blood loss
- vein puncture
Blood tests can offer a good snapshot of your overall health.
They’re also a good way to catch illness or disease early, and to see how well your body responds to treatments for various conditions.
Many people get routine blood tests done at least once a year. Talk with your doctor to learn whether there are any other tests you may need to ensure your optimal health.