Osmotic fragility

Answer 1

Definition

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

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

In the laboratory, red blood cells are tested with a solution that makes them swell, in order to determine 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, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

This test is performed to detect hereditary spherocytosisand thalassemia. Hereditary spherocytosis makes red blood cells more fragile than normal. Some red blood cells in patients with thalassemia are more fragile than normal, but a larger number are less fragile than normal.

Normal Values

A negative test is normal.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

• Thalassemia
• Hereditary spherocytosis

What the risks are

Veins and arteries vary in size from one patient 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 light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Golan DE. Hemolytic anemias: red cell membrane and metabolic defects. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007: chap 165.

Gallagher PG, Jarolim P. Red Blood Cell Membrane Disorders. In: Hoffman R, Benz EJ, Shattil SS, et al, eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 46.

Answer 2

Definition

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

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

In the laboratory, red blood cells are tested with a solution that makes them swell, in order to determine 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, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

This test is performed to detect hereditary spherocytosisand thalassemia. Hereditary spherocytosis makes red blood cells more fragile than normal. Some red blood cells in patients with thalassemia are more fragile than normal, but a larger number are less fragile than normal.

Normal Values

A negative test is normal.

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

What abnormal results mean

• Thalassemia
• Hereditary spherocytosis

What the risks are

Veins and arteries vary in size from one patient 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 light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

References

Golan DE. Hemolytic anemias: red cell membrane and metabolic defects. In: Goldman L, Ausiello D, eds. Cecil Medicine. 24th ed. Philadelphia, Pa: Saunders Elsevier; 20011:chap 164.

Gallagher PG, Jarolim P. Red blood cell membrane disorders. In: Hoffman R, Benz EJ, Shattil SS, et al., eds. Hematology: Basic Principles and Practice. 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2008:chap 46.

Reviewed By

Review Date: 02/08/2012

Todd Gersten, MD, Hematology/Oncology, Palm Beach Cancer Institute, West Palm Beach, FL. Review provided by VeriMed Healthcare Network. Also reviewed by Linda J. Vorvick, MD, Medical Director and Director of Didactic Curriculum, MEDEX Northwest Division of Physician Assistant Studies, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington; David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.