glucose-6-phosphate dehydrogenase (G6PD) in erythrocytes
Indications
- evaluation of G6PD deficiency
Contraindications
- do not measure during an acute attack
- levels are elevated in erythrocytes[5]
Reference interval
- Normal is complete decolorization within 20-60 minutes. 5-15 U[5], 12 +/- 2 U/g Hgb[6], 4 +/- 1 U/mL[6]
Principle
G6PD deficiency is an inborn error of metabolism, or genetic defect, that occurs in 10-15% of American Negroes, & is common in other dark-skinned races. Individuals with a G6PD deficiency will experience an acute hemolytic episode after ingestion of certain drugs & food products. (Example: Primaquine, fava beans). G6PD deficiency is inherited as a partially dominant sex-linked (X chromosome) gene. Affected males usually show full expression (presumably homozygous); females usually show an intermediate expression (heterozygous). An occasional female may show full expression (presumably homozygous).
Normally 90% of glucose is broken down through glycolysis, which supplies energy for NADH methemoglobin reductase, an enzyme which converts methemoglobin to hemoglobin. The pentose-phosphate shunt is an alternative pathway in which the enzyme glucose-6-phosphate dehydrogenase enhances the breakdown of glucose-6-phosphate to ribulose-5-phosphate. Concurrent with this breakdown, G6PD generates NADH from NAD which in turn supplies reduccing equivalents for NADH methemoglobin reductase, which also converts methemoglobin to hemoglobin.
Clinical significance
Three G6PD variants occur with high frequency:
G6PD variants with severely reduced activity (e.g., Mediterranean & Mahidal) may cause hemolytic disease of the Newborn. A small proportion of persons with G6PD Mediterranean have mild chronic hemolysis. Persons with G6PD Mediterranean are also subject to favism, an acute & very severe hemolytic crisis,often with fatal outcome, precipitated by ingestion of fava beans (Vicia fava). These individuals are also susceptible to severe hemolysis following ingestion of various pharmaceuticals & as a consequence of infections.
Hemolysis in blacks with G6PD deficiency is rarely severe or life-threatening.
Hemolysis is associated with ingestion 8-aminoquinolines & other pharmaceuticals.
- antimalarial drugs of the 8-aminoquinoline type
- older sulfonamides such as sulfanilamide
- sulfones
- nalidixic acid
- nitrofurantoin
- large doses of vitamin C
Decreases
Specimen
Anticoagulated blood (heparinized or EDTA), a minimum of 0.5 mL G6PD activity in whole blood may decline if sample is refrigerated (2-6 C), but may still fall within the normal range after a week or more at this temperature.
More general terms
Additional terms
- glucose-6-phosphate 1-dehydrogenase (G6PD)
- glucose-6-phosphate dehydrogenase [G6PD] deficiency; chronic non-spherocytic hemolytic anemia (CNSHA)
Component of
References
- ↑ Reference Procedure for Glucose-6-Phosphate Dehydrogenase (G6PD) Deficiency Test. Sigma Diagnostics Procedure #400, 1989.
- ↑ Tietz, Norbert W., Ph.D., Textbook of Clinical Chemistry, W.B. Saunders Company, Philadelphia, PA, 1986, p. 1498-1499.
- ↑ Doxiadis, S.A., Fessas, F.H., Valaes, T., & Mastrokalos, N., Lancet, 297, Feb. 11, 1961.
- ↑ Medical Laboratory & Clinical Pathology, Sanders, 2nd Edition, Cornbloth & Schwartz, 1966.
- ↑ 5.0 5.1 5.2 Medical Knowledge College of Physicians, Philadelphia 1998, 2018.
- ↑ 6.0 6.1 6.2 Clinical Guide to Laboratory Tests, 3rd edition, NW Tietz ed, WB Saunders, Philadelphia, 1995
- ↑ Glucose-6-Phosphate Dehydrogenase Laboratory Test Directory ARUP: http://www.aruplab.com/guides/ug/tests/0080135.jsp
Patient information
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