DLC Test (Differential Leukocyte Count): Why and How is it Done?

The DLC test, known as the Differential Leukocyte Count Test in full, evaluates the percentage of different components of the white blood cells. These white blood cells are also referred to as WBCs or leukocytes. This test can identify immature leukocytes and other abnormalities that indicate certain medical conditions.`

The six major types of leukocytes that are present in a blood sample are lymphocytes, eosinophils, monocytes, neutrophils, basophils, and band or young neutrophils. Leukocytes play an essential role as a part of our immune system. They protect us from infections caused by foreign agents like bacteria, viruses, protozoa, and microbes.

Why is the DLC Test done?

Your doctor may recommend a DLC test if they suspect the presence of certain medical conditions like infections, anemia, leukemia, autoimmune disorders, etc. These diseases generally manifest themselves through symptoms like fever, chills, headache, and body pain. Some other symptoms are unexplained bruising, fatigue, weakness, sudden weight loss, etc.

This test may be recommended as a part of a routine checkup or along with the complete blood count (CBC) test. It may also be advised when a patient is undergoing treatment for some other medical condition.

Prerequisites of the DLC Test

There are no preparations that patients need to follow before or after taking the DLC test unless your doctor advises otherwise. Some blood tests require patients to fast, that is, avoiding eating and/or drinking for a certain number of hours before taking the test. This is usually not recommended for the DLC test.

There are certain medications that are known to interact with the accuracy of the results of this test.  If you are currently taking any medications, it is important to let your doctor know.

These medications include prescription drugs, non-prescription or OTC (over-the-counter) drugs, vitamins, supplements, and herbals. If your medications are amongst those that are known to adversely affect the results of this test. Your doctor will most probably advise you to not take those medications for a few days before and/or after undergoing this test.

Closely follow the instructions of your doctor in this regard.

Understanding the Results

The normal range of percentages for each type of leukocyte is considered to be:

Lymphocytes – 20% to 40%

Eosinophils – 1% to 4%

Monocytes – 2% to 8%

Neutrophils – 40% to 60%

Basophils – 0.5% to 1%

Band – 0% to 3%

When should it be repeated?

If the results of the DLC test showed abnormalities when it was taken for the first time, you are likely to be recommended a repeat test sometime later. This will enable your doctor to monitor the percentages of the types of leukocytes and become aware of any improvements. The future course of treatment will be based on the improvements or worsening in the result of the repeat test.

If your test results are within the normal range, your treatment will be discontinued. In some cases there may be no change in the test results or the results may be worse. It is a clear indicator that the treatment has not been effective. The doctor will then increase the dosage of medications or recommend an alternate course of treatment. Later a repeat test will be done.

Procedure

For the traditional method of the DLC test, a healthcare expert selects a vein in your arm that is suitable for drawing blood as a sample. Usually, one of the veins that are located in the inner elbow area of the upper arm or in the hand is chosen for this purpose. He/she cleans the relevant area with an antiseptic solution.

This area is then wrapped with an elastic band to make the vein swell and become more prominent. Next, the healthcare professional inserts the needle into the vein to draw blood until the vial of the injection is full. The bleeding from the puncture site is stopped with cotton wool. A bandage is applied to the wound to accelerate the process of healing.

It generally does not take more than a few minutes to complete the entire procedure. The pain differs between people from a slight to a sharp pinch. The blood sample collected is sent to a laboratory for studying under a microscope. It can also be studied manually or through the tech-advanced automated procedure.