What to Expect During and After the EOS Blood Test

What to Expect During and After the EOS Blood Test
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Eosinophils are a type of white blood cell that becomes active when certain infections, allergic diseases, or medical conditions are present. An EOS blood test is done to measure how many eosinophils are in the body. When there are too many or too little of these white blood cells, it can indicate a disease or condition.

How is the Test Performed?

The blood that is tested is drawn from a vein, most often a vein in the hand or arm. The puncture site will be cleaned with an antiseptic and a tourniquet applied just above the puncture site. A needle is then inserted into the chosen vein, where a syringe or airtight vial collects enough blood for the test. The tourniquet is then removed, the healthcare provider ensures the vial or syringe has enough blood, then the needle is removed from the vein. The puncture site is then covered and pressure is applied to stop any bleeding.

How to Prepare for the Test

Adults will not have to do anything to prepare. However, they must tell their doctor about any medications they take regularly before this blood test. Certain medications can increase the amount of eosinophils a patient has, including:

  • Certain laxatives including psyllium
  • Interferon
  • Amphetamines
  • Certain antibiotics
  • Tranquilizers

What to Expect During this Blood Test

Most patients will do fine with this test and any discomfort will be very minor. What patients feel vary and some describe what they feel as moderate pain, some describe it as a prick, and some state they feel some stinging. After the blood is drawn and the needle is removed, there may be some throbbing and bruising.

Why is an EOS Blood Test Performed?

If the results of another blood test called a blood differential are abnormal, this blood test may be ordered. If a specific disease is suspected, this test may also be ordered. This test may assist in diagnosing:

  • An allergic reaction (or how severe it is)
  • A parasitic infection
  • Acute hypereosinophilic syndrome
  • Cushing’s disease in its early stages

What do the Results Mean?

When an eosinophil count is higher than it should be it is most often due to parasitic infection or an allergic disease. It may also indicate:

  • Asthma
  • Eczema
  • Leukemia
  • Autoimmune diseases
  • Hay fever

If an eosinophil count is lower than it should be it may indicate:

  • Certain steroids in the body being overproduced
  • Alcohol intoxication

Possible Risks of this Blood Test

When blood is taken from a vein, the risks are minimal, but all patients should still be aware of what they are. The possible risks include:

  • Lightheadedness or fainting
  • Infection
  • Excessive bleeding
  • Hematoma


Medline Plus. (2009). Eosinophil Count – Absolute. Retrieved on July 15, 2010 from Medline Plus: https://www.nlm.nih.gov/medlineplus/ency/article/003649.htm

Blood Test Guide. (2010). What is an EOS Blood Test? Retrieved on July 15, 2010 from Blood Test Guide: https://www.bloodtestguide.com/what-is-an-eos-blood-test.html

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Phlebotomy: Bubbels – sxc.hu