By Heidi Moawad, MD 

Updated on September 15, 2023

 Medically reviewed by Steffini Stalos, DO

Blood testing is a routine part of preventive health. We use them to monitor health and diagnose any medical problems that may occur.

These tests are generally simple, with almost no risk and minimal discomfort.

This article discusses the uses and types of blood tests and how to interpret the results.

What Can Blood Tests Detect?

When you have a blood test, a sample of blood is sent to a laboratory and tested for different cells and substances. Often, the amount, size, and concentration of the cells and substances are reported with numerical values that are compared to standard or ideal values. 

Examples of what can be tested in the blood include:

• Glucose (blood sugar)

• Types of cells, such as white blood cells, red blood cells, and platelets 

• Minerals, such as potassium, calcium, and iron 

• Fat and cholesterol 

• Vitamins, such as vitamin B12 and vitamin D 

• Hormones, such as thyroid hormones and estrogen

• Inflammatory markers, such as erythrocyte sedimentation rate (ESR or sed rate) and antinuclear antibodies (ANA)

• Tumor markers, such as CA 125

• Genetic markers¹

• Toxins, such as lead

• Drugs or medications²

• Oxygen and carbon dioxide levels

Blood tests can be used to detect signs of health risks, infection, and the balance of fluids and minerals in the blood. They can also be used as an assessment of physical functions.

Blood Test Process

Blood tests can measure certain components when the blood is taken to a lab and combined with specific chemicals that detect certain cells, proteins, hormones, and enzymes.² Blood test technology is always improving, and some blood tests can identify diseases that couldn’t be easily diagnosed years ago.

Types of Blood Tests

If you are having a blood test, you will have an order that specifies which tests you need. Some blood tests require preparation to ensure accurate results. Preparation may involve fasting (not eating or drinking) for a set amount of time prior to having the test or making certain medication adjustments.

During the test, the blood is placed into tubes that correspond to the type of tests you are getting. Some tubes contain material to maintain the components that are being tested. Then the sample is sent to the laboratory for testing.

Below are common types of blood tests.

Complete Blood Count (CBC)

A complete blood count is a very common blood test, and it measures the number of blood cells and the percentage of each type of blood cell. 

A CBC includes:

• Red blood cells (RBCs): RBCs carry oxygen and carbon dioxide throughout the body. The number of RBCs is reported, as well as their size and hemoglobin (the protein that carries oxygen) and hematocrit (the percentage of blood volume that is RBCs) levels. 

• Platelets: These are small cell particles that help the blood clot, a process that promotes healing and prevents excess bleeding.

• White blood cells (WBCs): Several types of WBCs, including neutrophils, monocytes, and erythrocytes, help the body fight infections and heal from disease. 

A CBC also provides information about the size of each blood cell type. The results can help your healthcare provider determine if you may have anemia (a low number of healthy red blood cells), an infection, or indicators of other conditions.

 Understanding Your Complete Blood Count

Basic Metabolic Panel (BMP)

The basic metabolic panel blood test measures glucose, calcium, sodium, potassium, chloride, creatinine, blood urea nitrogen (BUN), and bicarbonate (CO2).

Creatinine and BUN levels can reflect how well the kidneys are functioning.³ Sodium, potassium chloride, and calcium are electrolytes (charged minerals) that the body must keep in balance in the bloodstream. Bicarbonate reflects whether there is an imbalance in acid and base in the blood.⁴

Severe abnormalities in these values can often indicate a medical emergency.

Comprehensive Metabolic Panel (CMP)

A comprehensive metabolic panel test is similar to a BMP, and it also includes protein, albumin (a type of protein), and liver function tests.

Lipid Panel

A lipid panel provides the count of triglycerides (a type of fat), low density lipoprotein (LDL), high density lipoprotein (HDL), and total cholesterol. Lipoproteins carry cholesterol, a waxy substance that is needed by the body but that can build up in blood vessels and cause problems.

These values reflect cardiovascular and stroke (a blockage of blood flow or bleeding in the brain) risk, with high levels of most lipid types usually associated with a high risk.⁵ However, low HDL (the so-called good cholesterol) levels are considered a risk factor for heart disease and stroke.

Other Blood Tests

Blood tests can be used to detect specific hormones, proteins, enzymes, or markers in the blood that are indicators of various conditions. These types of tests may be used to diagnose and monitor a condition, as well as evaluate treatments for the condition.

People often wonder why a variety of tubes are used to collect blood. Which are drawn depend on the test, as some need specific additives in the tube. More than one of the same type of tube may be drawn because they are being sent to different sections of the laboratory or to different laboratories.

Results for tests sent to a laboratory that performs specialized tests may take longer to be reported than for standard blood tests.¹

How Often Should You Get Blood Work Done?

Blood test frequency can vary. The types of blood tests you may need, and the collection schedule will depend. Factors may include if you have a chronic condition, are experiencing new systems, or need medical screening tests.

The cadence of blood work depends on the reason for the blood draw. This can include:

• Routine blood tests: Depending on your age and risk factors, you might need to have a lipid panel as part of standard health maintenance to determine whether your lipid levels could be putting you at risk of disease.

• Pregnancy: Blood work is used to monitor the pregnant person's blood glucose levels.

• Monitoring disease or response to treatment: Sometimes blood tests are needed at certain scheduled intervals to monitor disease or response to treatment. For example, suppose you are having treatment for systemic lupus erythematosus (SLE, the most common type of lupus). In that case, you might need periodic blood tests to monitor your white blood cell (WBC) count and erythrocyte sedimentation rate (ESR). 

• Diagnosis: Blood tests may also be needed to help diagnose a suspected medical condition. For example, if you have unexplained weight gain, low energy, and have been feeling cold, you might need thyroid blood tests to determine your thyroid disease. 

Understanding Blood Test Results 

Usually, blood test results are reported as numbers. The value that’s being measured—such as calcium or hemoglobin—is compared to the standard or ideal value. 

The reported numbers from your blood test are not usually enough to make a diagnosis. You and your healthcare provider will need to discuss your overall health to put the numbers in perspective in terms of what they reflect about your health.²

Awaiting Results

It can take hours, days, or longer for a blood test result to come back. If you are having an emergency blood test in a hospital, it might take less than an hour. It can take longer for results of specialized test results to come back.

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.⁶ The plus sign indicates Rh markers, while the minus sign indicates Rh-negative.

Blood types include: 

• 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.⁶ However, outside of emergencies, it's preferred that type-specific, crossmatched blood be given.

 How Can You Find Out Your Blood Type?

Summary 

Blood tests are used to measure different components of blood, and the measurements are an indication of health. You might need some blood tests as part of routine health maintenance, to assess certain symptoms, or to monitor disease progression and treatment.