Osmotic fragility test

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Osmotic fragility is a blood test to detect whether red blood cells are more likely to break down.

Alternative Names

Spherocytosis - osmotic fragility; Thalassemia - osmotic fragility

How the Test is Performed

A blood sample is needed.

In the laboratory, red blood cells are tested with a solution that makes them swell. This determines how fragile they are.

How to Prepare for the Test

No special preparation is necessary for this test.

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. This soon goes away.

Why the Test is Performed

This test is done to detect conditions called 

and . Hereditary spherocytosis makes red blood cells more fragile than normal. With thalassemia, some red blood cells are more fragile than normal, but more of them are less fragile than normal.

Normal Results

A normal test result is called a negative result.

Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your health care provider about the meaning of your specific test results.

What Abnormal Results Mean

An abnormal result indicates 1 of these conditions:

  • Thalassemia
  • Hereditary spherocytosis


Veins and arteries vary in size from one person to another, and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood buildup under the skin)
  • Infection (a slight risk any time the skin is broken)


Gallagher PG. Red blood cell membrane disorders. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, Anastasi J, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 43.

Gallagher PG. Hemolytic anemias. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 161.

Version Info

  • Last reviewed on 2/11/2016
  • Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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