Glucose-6-Phosphate Dehydrogenase (G-6-PD), Quantitative, Erythrocytes
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Hemolytic disease may be associated with deficiency of erythrocyte enzymes. The most commonly encountered is a deficiency of glucose-6-phosphate dehydrogenase (G6PD).
The G6PD locus is on the X chromosome and, thus, G6PD deficiency is a sex-linked disorder. Affected males (hemizygotes) inherit the abnormal gene from their mothers who are almost always asymptomatic carriers (heterozygotes). More than 300 molecular variants of G6PD are known, and the clinical and laboratory features of G6PD deficiency vary accordingly. With some variants, there is chronic, life-long hemolysis, but much more commonly, the condition is asymptomatic and only results in susceptibility to acute hemolytic episodes, which may be triggered by some medications, ingestion of fava beans, viral, or bacterial infections. It is also associated with neonatal hyperbilirubinemia.
The major G6PD variants occur in specific ethnic groups. Thus, knowledge of the ethnic background of the patient is important. G6PD deficiency has very high frequency in Southeast Asians and is the most common cause of hemolytic disease of the newborn in Southeast Asian neonates. It is also seen in persons of African and Mediterranean descent.
Rasburicase therapy is contraindicated in patients with G6PD deficiency. Deficiency can be assessed by enzymatic and/or genetic assays. If deficient status can be unambiguously assigned by genotyping, that is sufficient. However, due to the limitations of genetic testing, in most cases it is necessary to perform G6PD enzyme testing to assign G6PD status (adapted from Relling et al).(1)
Evaluation of individuals with Coombs-negative nonspherocytic hemolytic anemia
Rapid testing to assess glucose-6-phosphate dehydrogenase (G6PD) enzyme capacity prior to Rasburicase therapy
Abnormal values are usually 0% to 20% of normal mean. Intermediate values can occur in some genetic variants and in female carriers.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
In African Americans with the glucose-6-phosphate dehydrogenase (G6PD) A-variant, normal values may be measured for several weeks following hemolysis. This is not the case with other G6PD variants that predispose to hemolysis.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
> or =12 months: 8.8-13.4 U/g Hb
Reference values have not been established for patients who are <12 months of age.
Clinical References Provides recommendations for further in-depth reading of a clinical nature
1. Relling MV, McDonagh EM, Chang T, et al: Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines for rasburicase therapy in the context of G6PD deficiency genotype. Clin Pharmacol Ther 2014 Aug;96(2):169-174
2. Beutler E: Glucose-6-phosphate dehydrogenase deficiency. In Hematology. Fifth Edition. Edited by E Beutler, MA Lichtman, BS Coller, TJ Kipps. New York, McGraw-Hill Book Company, 1995, pp 564-586