An important issue has come up with a few private consults lately and I want to be sure to mention it here too.

Red blood cells contain an enzyme that will degrade insulin. Any amount of hemolysis in the sample for insulin determination will lower the result.  Even slight hemolysis could drop the result by about 20% and the more hemolysis there is, the greater the effect.

Spinning the sample and removing the plasma or serum ASAP will limit the effect but since most hemolysis occurs during the collection of the blood it can still be a significant problem.  Once the  cells are lysed (hemolysis) the enzyme is free in the plasma or serum.

Keeping the sample at refrigerator temperature (4 C/40 F) reduces the insulin destruction but not completely and any rewarming during shipping and handling ramps it up again.

Effect of Hemolysis on the Concentration of Insulin in Serum Determined by RIA and IRMA

 

Eleanor in PA
www.drkellon.com
EC Co-owner
Feb 2001