Osmotic fragility

What the risks are:

• 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

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.