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G6PD diagnosis deficiency testing is based on direct measurements of G6PD activity in a population of RBCs. In the setting of an acute hemolytic episode, the RBCs with the most severely reduced G6PD activity will have hemolyzed, and thus their G6PD activity will not be measured in the assay. This situation can produce false-negative results in some patients who are tested in the midst of a severe hemolytic episode due to other causes.
False-negative results are also seen during the period of initial reticulocytosis, when there is the highest proportion of reticulocytes, which typically have normal G6PD activity.
Thus, if initial testing is negative and a suspicion for G6PD deficiency remains, testing should be repeated approximately three months after the hemolytic episode has resolved.
Practice points
- G6PD test done during neonatal period are only screening tests as definitive Quantitative assay are best done after age of 3 months.
- Sample for G6PD screening is collected in EDTA vials to prevent clotting and should be processed within 4 hours of collection, as a delay can alter results.
LIST OF DRUGS CONTRAINDICATED IN G6PD DEFICIENCY
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