Blood tests can be used to help a doctor identify a variety of health conditions, including infections, anemia, high cholesterol, vitamin deficiencies, organ failure, HIV, cancer, diabetes, and more.
Doctors use blood tests to analyze the behavior of substances like proteins, cells, or chemicals in your blood.
This can give them a picture of your overall health and help them diagnose different diseases, monitor chronic conditions, assess your organ function, and determine your immune system strength.
Regular blood testing is one of the most important ways to keep track of your overall physical well-being. We’ve partnered with Lifeforce to bring you this overview article on blood tests.
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.
You would typically undergo a blood test in the following cases:
- During your annual physical exam: Your doctor may order a general blood test such as the complete blood count (CBC).
- You’re at risk of a health condition: You may need to undergo a specific blood test if you have a higher chance of developing a specific disease or condition or if you have a known genetic mutation that can cause a condition.
- You have a known condition: Sometimes,you already have a diagnosis, but your doctor needs to know how your condition is progressing or to evaluate your treatment.
- You’re having symptoms: If you are experiencing symptoms, your doctor may need to run a blood test to confirm a suspected diagnosis or to see if you need more specialized testing.
- You’re pregnant: During pregnancy, your doctor will do a CBC and test your blood type.
- Before surgery: You may need to do a blood test if your surgeon wants to check for anything that might put you more at risk during the procedure, such as excessive bleeding, for example.
- You want to optimize your health: Knowing the 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.
Regarding routine blood tests, recommendations call for, at minimum, a lipid test starting at age 20 and every 5 years after that for people with a low risk of heart disease.
For people at a higher risk of heart disease, more frequent lipid testing may be necessary.
In addition, you should get a blood glucose test if you are 40-70 years old and overweight or have obesity.
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: 4.5–6.1 × 106/ microleter (μL); female: 4.0–5.4 × 106/μL
|white blood cells (immune system cells in the blood)
|male: 4.0–10.8 × 103/μL
female: 4.0–10.8 × 103/μL
|platelets (the substances that control the clotting of the blood)
|male: 150–400 × 103/μL
female: 150–400 × 103/μL
|hemoglobin (protein within the red blood cells that carries oxygen to organs and tissues and carbon dioxide back to the lungs)
|male: 13.0–17.0 grams/deciliter (g/dL); female: 12.0–16.0 g/dL
|hematocrit (percentage of blood made of red blood cells)
|male: 40–52%; female: 37–47%
What it indicates:
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.
[the terms “male” and “female”]
In this article, we use “male and female” to refer to someone’s sex as determined by their chromosomes and “men and women” when referring to their gender (unless quoting from sources using nonspecific language).
Sex is determined by chromosomes, and gender is a social construct that can vary between time periods and cultures. Both of these aspects are acknowledged to exist on a spectrum both historically and by modern scientific consensus.
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.
What it indicates:
Abnormal results may indicate:
- kidney disease
- electrolyte imbalances
Your doctor will perform follow-up tests to confirm a diagnosis.
The Lifeforce Diagnostic is an at-home blood test designed to gather data on 40+ biomarkers that impact your health and longevity, including your metabolic condition, hormone health, and key risk factors for disease. Your diagnostic includes an at-home blood draw from an experienced phlebotomist, a telehealth consultation with a Lifeforce clinician, and a personalized plan that consists of expert insights, lifestyle improvements, nutraceuticals, and hormone and peptide therapies.
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
What it indicates:
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:
|• bile duct blockage
• gallbladder inflammation
• Paget’s disease
|• bone metabolism disorders
• heart surgery
• zinc deficiency
• liver cancer
• liver damage
• heart conditions
|• 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.
For HDL cholesterol, 60 milligrams per deciliter (mg/dL) or above is considered to be heart-healthy, while under 40 mg/dL is a major risk factor for heart disease.
For LDL cholesterol, 100 mg/dL or below is optimal for good health, while 160 mg/dL or over is dangerously high.
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)
What it indicates:
Abnormal levels of these hormones can indicate numerous conditions, such as:
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.
Here are the normal ranges for the enzymes listed above:
- hs-cTn: <1 ng/mL
- BNP: <100 picograms per milliliter (pg/mL)
- NT-proBNP: ≤300 pg/mL
- CK: 30–200 units per liter (U/L)
- CK-MB: 0–12 IU/L
What it indicates:
Abnormal enzyme levels can indicate many conditions.
Common enzymes tested include:
- High-sensitivity cardiac troponin (hs-cTn):This is a heart enzyme that can leak into your blood and result in heart injury.
- B-type natriuretic peptide (BNP) and N-terminal pro b-type natriuretic peptide (NT-proBNP): These substances are created in the heart. High levels may be an indication of congestive heart failure.
- Creatine kinase (CK): This enzyme is 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.
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
Clotting is a crucial process that helps you stop bleeding after a cut or wound. However, 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.
What it indicates:
Results from this test can be used to diagnose:
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 females, 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
- premature puberty in females
- use of steroid medications
What it indicates:
High levels in males or females 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.
- <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
What it indicates:
High CRP levels indicate inflammation from a variety of causes, including:
- bacterial or viral infection
- autoimmune diseases, such as Lupus or rheumatoid arthritis
- inflammation related to diabetes
- inflammation related to physical trauma or from habits like smoking
Before any blood test, ask your doctor for any instructions you need to follow to make sure the results are accurate.
Also, let your doctor know about any medications and supplements you’re taking in case they could affect the results.
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 also 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.
Where do I get blood work done?
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, such as in your doctor’s office during an appointment.
- 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.
Do I fast?
Some tests will require you to fast for 8-12 hours beforehand. That’s because 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.
Some common tests that may require fasting include:
- cholesterol tests
- blood sugar tests
- liver function tests
- kidney function tests
- basic metabolic panel
The blood test procedure
In a blood test procedure, a healthcare professional such as a nurse or a phlebotomist will
- Clean the area on your arm where they’ll draw the blood from.
- Tie a rubber band to your upper arm to help make your veins more visible, and ask you to make a fist.
- Put a needle attached to a tube gently into a vein to draw blood.
- Remove the needle from the skin and take the rubber band off your arm when the collection is complete.
- Cover 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
How much blood is drawn in a blood test?
The amount is usually just enough to fill a small vial of blood. However, if you’re getting more than one test, you may have to fill out several vials.
On average, this is usually around 5-20 milliliters (ml), which is equal to a few teaspoons (tsp) to a few tablespoons (tbsp). For comparison, donating blood typically involves giving around 450 ml.
How long does it take to get results?
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.
How do I read blood test results?
While every laboratory or test-providing company may structure its 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 measures the quantity of something, such as 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 the 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 can see where your result falls in the range.
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.