All About Blood Tests

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 include your thyroid, liver, or kidneys.

Your doctor can also use blood tests to search for markers of diseases and health conditions such as:

• diabetes
• HIV
• anemia
• cancer
• 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.

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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.

Here’s the typical range of results, although every laboratory may have its own range that varies slightly:

Component	Normal range
red blood cells (cells responsible for carrying oxygen throughout the body)	male: 4.3–5.9 million/mm 3 ; female: 3.5–5.5 million/mm 3
white blood cells (immune system cells in the blood)	4,500–11,000/mm 3
platelets (the substances that control the clotting of the blood)	150,000–400,000/mm 3
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 indicate:

• nutritional deficiencies, such as vitamin B6 or B12
• anemia (iron deficiency)
• clotting problems
• blood cancer
• infection
• 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:

• calcium
• glucose
• sodium
• potassium
• bicarbonate
• chloride
• blood urea nitrogen (BUN)
• creatinine

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.

Abnormal results may indicate:

• kidney disease
• diabetes
• 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:

• albumin
• 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 • cirrhosis • gallbladder inflammation • gallstones • hepatitis • Paget’s disease	• bone metabolism disorders • heart surgery • malnourishment • zinc deficiency
ALT	• cirrhosis • hepatitis • liver cancer • liver damage	considered normal
AST	• cirrhosis • heart conditions • hepatitis • mononucleosis • (mono)pancreatitis	considered normal
bilirubin	• abnormal red blood cell destruction (hemolysis) • adverse medication reactions • bile duct blockage • Gilbert’s syndrome • hepatitis	not a concern

4. Lipid panel

This test checks levels of two types of cholesterol:

• 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 ranges for each type:

High	Low/Optimal
HDL	>60 mg/dL	male: 160 mg/dL	higher the level, the higher the risk of heart disease:

• 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

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 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 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 includes your 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 get some 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 following :

• 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.

To perform a blood test, the nurse or technician:

1. Cleans the area on your arm where they’ll draw the blood from.
2. Ties a rubber band to your upper arm to help make your veins more visible, and asks you to make a fist.
3. Puts a needle attached to a tube gently into a vein to draw blood.
4. Removes the needle from the skin and takes the rubber band off your arm when the collection is complete.
5. 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