Osmotic fragility test

Definition

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 hereditary spherocytosis and thalassemia. Hereditary spherocytosis and thalassemia cause red blood cells to be more 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 may indicate one of these conditions:

• Thalassemia
• Hereditary spherocytosis

Risks

There is little risk involved with having your blood taken. 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
• Multiple punctures to locate veins
• Hematoma (blood buildup under the skin)
• Infection (a slight risk any time the skin is broken)

References

Gallagher PG. Hemolytic anemias: red blood cell membrane and metabolic defects. In: Goldman L, Cooney KA, eds. Goldman-Cecil Medicine. 27th ed. Philadelphia, PA: Elsevier; 2024:chap 147.

Gallagher PG. Red blood cell membrane disorders. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 46.