Sugar-water hemolysis test

Alternative names 
Sucrose hemolysis test

This is a blood test to detect increased fragility of red blood cells by swelling them in low-salt solution.

How the test is performed

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to swell with blood.

A needle is inserted into the vein, and the blood is collected in an airtight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

The blood is analyzed in a laboratory.

How to prepare for the test
There is no special preparation needed for this test.

For infants and children, the preparation you can provide for this test depends on your child’s age and previous experience. For general information regarding how you can prepare your child, see the following topics:

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 ordered for suspected paroxysmal nocturnal hemoglobinuria (PNH), and for any hemolytic anemia of unkown origin. PNH red blood cells are unusually susceptible to complement (a component of the body’s defense mechanism).

When a low-salt solution containing sucrose (sugar) is added to these cells, the complement is activated, binds to the cells, and bursts them.

Normal Values

  • negative: less than 5% hemolysis (red blood cell breakdown)  
  • positive: greater than 10% hemolysis

What abnormal results mean

  • paroxysmal nocturnal hemoglobinuria (PNH)  
  • autoimmune hemolytic anemias and Leukemia may give false positive result

What the risks are

Risks associated with having blood drawn are slight:

  • excessive bleeding  
  • fainting or feeling light-headed  
  • hematoma (blood accumulating under the skin)  
  • infection (a slight risk any time the skin is broken)  
  • multiple punctures to locate veins

Special considerations

A negative test does not rule out PNH. False-negative results may occur if the serum is depleted of complement.

Johns Hopkins patient information

Last revised: December 6, 2012
by Simon D. Mitin, M.D.

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