The ABCs of Blood Tests

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The ABCs of blood tests • Cellular evaluations • Biochemical analysis • Molecular profiles • How to fast before a blood test

The ABCs of blood tests With this simple guide, know what kind of blood tests you are shedding your blood for.

One in every 10 persons has a fear of needles, or trypanophobia. But all of us still probably get nervous at the thought of getting a blood test. And since blood flows through prac-

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tically every part of your body, blood tests are a great way to evaluate how your organs are, and how well they are functioning. Although a few tests may be done from blood coming from a prick, most blood tests require more than just a few drops, so the blood has to be drawn through a needle from the vein. Some may even require a puncture to the artery.

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How to fast before a blood test

There are many different kinds of blood tests, each one checking for different organs, different biological processes,

Some blood tests require “fasting” or not taking in food, several hours before blood is drawn. These are for tests that may be affected by the intake of food.

and different diseases. These tests can be

The most common tests that require fast-

classified into three groups:

ing are blood sugar and blood lipids/ cholesterol.

• Cellular evaluations – tests that evaluate

• Molecular profiles – tests that check

for specific macromolecules, such as

cells.

proteins, enzymes, antibodies,

• Biochemical analysis – these are tests

or DNA.

cells, such as blood cells or bacterial

that check for levels of specific chemicals

in the blood. Most of these chemicals

This guide of the most commonly requested

are naturally occurring or naturally

blood tests will help you the next time you

produced by body organs.

get a blood test. Normal values are not included, because these vary depending on a person’s age, gender, and the laboratory performing the test.

This means: Do not eat anything for a minimum of: • 8 hours for fasting blood sugar or

glucose tolerance test

• 12 hours for lipid/cholesterol/

triglyceride tests.

You are only allowed to drink water. Do not drink any juice, tea or coffee (even black, sugarless coffee or tea). Also, do not smoke, chew gum (even sugarless gum), or exercise. These activities may also affect fasting blood test results. After the blood has been collected, you may resume your normal diet.

Cellular evaluations Test

What it’s for

Complete blood count (CBC)

A CBC checks for all the blood cells all at the same time. This includes RBCs, WBCs, and platelets.

Red blood cells (RBC)

Usually assesses the health of RBCs, how well the body makes RBCs, and if they are dying quickly.

This can also be used to evaluate patients suspected of anemia (pale blood). The shape of the cells viewed under a microscope can also suggest various genetic illnesses or nutritional deficiencies.

White blood cells (WBC) Neutrophils Basophils Eosinophils Monocytes Lymphocytes

A WBC count evaluates not just your WBCs as a whole, but also the different kinds of WBCs found at any point in time. The WBC count taken together with the individual counts of each of the WBC subtypes can suggest different kinds of infections, cancers, immunologic disorders, or allergies.

Platelets

This checks for the number of platelets, which are responsible for preventing bleeding. Diseases that can lower platelets include viral infections, such as dengue; severe infections of the blood (sepsis); and diseases of the spleen and bone marrow.

Hemoglobin

This measures how much red pigment called hemoglobin is in your blood. Hemoglobin is responsible for transporting oxygen to the cells of the body.

Hematocrit

Hematocrit measures the ratio of the volume of cells in blood to the amount of fluid. A high hematocrit means thick blood, which may mean fluid is escaping the blood vessels. A low hematocrit may mean new RBCs are not being formed fast enough.

Erythrocyte sedimentation rate (ESR)

This is how fast your RBCs sediment within an hour. It is a general sign of inflammation in any part of the body. The ESR is also increased in pregnancy, anemia, arthritis, or some cancers.

Blood culture

This test is done by mixing blood with a culture medium that can allow bacteria to multiply. This test can show if there are bacteria causing infection, and what kind of bacteria is the culprit.

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Biochemical analysis Test

What it’s for

Blood sugar

It can detect diseases that increase blood sugar (such as diabetes), as well as lower it (hypoglycemia due to infections, acute malnutrition, other endocrine problems, or some medications).

Blood lipids (lipid profile)

This includes testing for good cholesterol, bad cholesterol, triglycerides, and other fats in the blood. This is most commonly used to assess one’s risk of getting a heart attack or stroke.

Electrolytes

The most common electrolytes measured are sodium, potassium, and chloride. These electrolytes can vary in different times of the day, depending on your state of health, nutrition, and activity.

Other electrolytes include calcium and magnesium, which can signify diseases that affect the bones, muscles, intestines, or kidneys.

Blood urea nitrogen (BUN)/Creatinine

These are two separate tests that are usually performed together to evaluate kidney function.

Uric acid

Uric acid is the byproduct of the metabolism of purines. Excess levels can lead to gout.

Molecular profiles Test

What it’s for

Liver function tests

This is a group of different tests on different molecules that are related to the functions of the liver.

The most common tests include alanine transaminase (ALT) and aspartate transaminase (AST).

These tests can go over the normal limit even in healthy people. However, elevations several times higher than normal signifies liver problems.

Thyroid function tests

These tests measure the activity of the thyroid gland. The most common tests include T4, T3, and thyroid stimulating hormone (TSH).

Prostate specific antigen

This is a marker of diseases in the prostate, such as benign prostatic hyperplasia or prostate cancer.

Lastly, it is important to note that laboratory tests are usually evaluated together, and not just individually. Body parts interact and do not operate alone. Hence, do not try to interpret your own lab results, but show them to a physician, who can not only interpret these results for you, but also advise you on next steps to improve your health.

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The information in this newsletter is not intended as a substitute for professional medical care.

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A Slice of Orange

is a newsletter designed to help clarify basic health information and offer juicy tips on uplifting your health.

Editorial team Alvin Delfin Christine Llenes-Delfin Ivan Olegario, MD