There are at least 3 different ways to test for G6PD Deficiency. Your doctor may order a genetic test specific to G6PD enzymes, or you can order your own full scale DNA test from 23andme which is very cost effective and provides you with a complete picture of all genetic risks, including G6PD. DNA testing is also eligible for FSA/HSA benefits, making it even more cost affordable.
The third possible testing method is to have a blood test of your G6PD enzyme activity. The usual reference range for this blood test is 7.0-20.5 U/g Hgb. Per the World Health Organization (WHO), clinically significant G6PD deficiency is enzyme activity less than 30% ( < 3 U/g Hb) in adults & children. Some patients might have a mild deficiency (3-8 U/g Hb) they are usually less at risk of oxidative stress, but should still understand potential oxidative stressors.
When should you schedule a blood test for G6PD enzyme levels? The best time to test is 2-3 months after your last suspected hemolytic episode.1 2 The reason is that G6PD levels vary between old and young red blood cells. G6PD levels are normal or near-normal in young, new red blood cells. But enzyme levels decrease up to 75% as red blood cells age. During hemolysis, a higher percentage of the older, more G6PD-deficient RBCs are destroyed. This leaves the new, less deficient cells to be tested, potentially masking a G6PD deficiency. A G6PD blood test may be falsely normal during a hemolytic episode, and up to 3 months after. Because of this, G6PD blood testing is not recommended until well after the acute hemolytic symptoms resolve.
If you had your blood tested during a crisis, you should be retested again AFTER the crisis.
Rebecca Rhew, J.D.