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Osmotic fragility How to Prepare:
Adult:
No special preparation is necessary for this test.
Infants and children:
The physical and psychological preparation you can provide for this or any test or procedure depends on your child's age, interests, previous experience, and level of trust. For specific information regarding how you can prepare your child, see the following topics as they correspond to your child's age:
How it Feels:
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 .
Risks:
- excessive bleeding
- fainting or feeling lightheaded
- hematoma (blood accumulating under the skin)
- infection (a slight risk any time the skin is broken)
- multiple punctures to locate veins
Why this Test is Performed:
This test is performed to detect hereditary spherocytosis and thalassemia .
Hereditary spherocytosis is a relatively common disorder characterized by red blood cells which are intrinsically defective because of their sphere-like shape. These cells have increased osmotic fragility.
Red blood cells from people with thalassemia show some cells with increased osmotic fragility, but a larger fraction with decreased fragility.
Normal Values:
A negative test is normal.
Abnormal Results:
Cost:
The estimated cost is $53.
Special Considerations:
Cells that are more spherical, with a decreased surface/volume ratio, have a limited capacity to expand in low osmolality solutions and lyse (rupture) at a higher concentration of sodium chloride than do normal biconcave red cells. These spherical cells are said to have increased osmotic fragility. Conversely, cells that are hypochromic and flatter have a greater capacity to expand and thus have decreased osmotic fragility.
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.
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