Definition and Overview

Also known as a blood test, blood work is the process of obtaining blood sample usually through the veins for lab examination. It is one of the most common methods of identifying or managing a health condition.

Blood is responsible for:

  • Carrying oxygen to various cells and tissues in the body

  • Transporting nutrients and sugar to cells, serving as their energy so they can continue with their metabolic processes.

  • Acting as a pathway for wastes or by-products of cellular processes, which are eliminated by the body in different ways

  • Getting carbon dioxide out of the body by transporting it to the lungs

Blood is generally composed of two parts: plasma, which is the fluid, and the cells, which can be platelets, red blood cells, and white blood cells.

Plasma makes up more than 50% of the entire composition of blood. It is the one that contains hormones, proteins, and glucose, among others.

As for the blood cells, each has its own role to play. The red blood cells are needed to transport oxygen while the white blood cells serve as the body’s defense against threats such as pathogens. Platelets, on the other hand, are the ones responsible for clotting. If the body doesn’t clot, a person can die due to massive blood loss.

Because of the complex makeup of blood and the various processes it undertakes, any changes in the “normal range,” depending on what the doctor is exactly looking for, may indicate a health issue or even a disease.

Who Should Undergo and Expected Results

A blood test may be recommended to anyone, including newborns and seniors. It may be undertaken to:

  • See if the person is healthy – A blood test may be carried out even without symptoms of a disease as part of a routine checkup.

  • Diagnose an illness – One of the primary reasons why doctors ask for a blood test is to confirm or diagnose a disease. Blood work may indicate hormone problems, diabetes, cancer, and blood-related disorders such as clotting and bleeding issues.

  • Check if the disease is managed properly – A person who is undergoing treatment may go through regular blood work to determine if he or she is responding positively to the treatment. Otherwise, the doctor may decide to either modify the treatment or stop it altogether

  • Rule out other diseases – More often than not, doctors already have suspicions based on the patient’s symptoms, but just to make sure, blood work can be undertaken to rule out the presence of other possible diseases

Blood tests are normally very quick, lasting no more than 10 minutes. The results, on the other hand, are usually presented in ranges. The report should indicate the normal range and whether the results fall within this range or not.

Falling above or below the normal range can cause anxiety and worry to the patient, but it’s not often an indication of a disease. Many factors can affect the results including the level of stress prior to the test. Also, although there are guidelines when it comes to ranges, they can change over time. Thus, a patient who has taken a blood glucose test may be considered “normal” today but could be prediabetic in the future based on the ranges alone. For this reason, blood tests are undertaken alongside other specific tests.

How Does the Procedure Work?

There are many ways to extract a blood sample from a patient. One of these is through pricking. In this method, a needle is used to prick a finger, allowing the blood to flow. A glass can then be used to obtain a smear.

Another—and it’s the most common—is blood drawing through the veins. A patient sits comfortably in a chair or may be lying down on a hospital table. A band is tied around the arm to make the veins more visible. Once the hospital staff, such as the nurse, has located the best vein, he or she slowly inserts a needle into the vein. After the required amount of blood is obtained, the needle is gently and slowly pulled out.

There’s also the arterial blood gas, in which the blood sample is used to determine the body’s metabolic and pulmonary functions (e.g., the levels of carbon dioxide and oxygen). In this procedure, blood is drawn directly from the artery. Two ideal locations are the femoral artery (in the groin) and the radial artery (in the wrist). If the artery is located elsewhere, a catheter may be used to serve as a guide. The catheter can then be removed once the procedure is completed.

Once the extraction is done, a piece of cotton with alcohol is given to the patient to minimize the bleeding.

The blood sample is then sent to the lab, where it goes through a centrifuge. This equipment can separate the many components of the blood so each can be studied more accurately. The process also means a single blood extraction can be used for different blood tests.

Depending on the number of the tests or the exact tests obtained, the results may be ready from a few hours to a couple of weeks. A hematologist or a pathologist can interpret the lab results, while the doctor can deliver the results to the patient for discussion.

Possible Risks and Complications

Blood extraction is generally safe. Occasionally, however, some patients develop hematoma or bruising. This is a condition wherein the blood pools outside of the blood vessels. This normally happens when the blood vessels themselves are broken, allowing the blood to leak. Fortunately, hematomas should not last very long, and it can be taken care of by a compress. It should also be localized, which means it affects only at the injected site.


  • American Association for Clinical Chemistry
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