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Lab Test: Glucose 6-Phosphate Dehydrogenase, G6PD Level

    Lab Test
    • Glucose 6-Phosphate Dehydrogenase (G6PD)
    • Measurement of glucose-6-phosphate dehydrogenase (G6PD) in red blood cells for the evaluation and management of enzyme deficiency. 
    • Used to identify G6PD deficiency in patients who have developed hemolysis after taking certain oxidizing drugs.  It is especially useful in males of certain ethnic populations who are susceptible to this genetic defect.
    Reference Range
    • Adults:  5-14 units/g/Hgb (0.1-0.28 microkat/L)
    • Negative (quantification)
    • 12.1±2 IU/g of hemoglobin
    • 146-376 units/trillion RBC
    • G6PD sequencing:  no mutation noted
    Indications & Uses
    • Suspected glucose-6- phosphate dehydrogenase (G6PD) deficiency - a decreased G6PD level indicates a hereditary enzyme deficiency that can predispose affected persons to hemolytic anemia.  The absence of G6PD leaves the erythrocyte vulnerable to oxidative damage, with the most frequent clinical manifestation being anemia.
    • Suspected glucose-6-phosphate dehydrogenase deficiency as cause of neonatal hyperbilirubinemia - neonates (especially males) with G6PD deficiency are at increased risk of developing hyperbilirubinemia.
    • Suspected sepsis - a decreased G6PD level predisposes to septic complications and anemia in trauma patients.
    Clinical Application
    • G6PD is an enzyme used in glucose metabolism. 
    • A deficiency causes precipitation of oxidized (causing the formation of Heinz bodies) hemoglobin and may result in hemolysis of variable severity.  It is a sex-linked, recessive trait carried on the X chromosome.  The full effect of this genetic defect is not manifested if the normal gene is present on a second X chromosome to oppose the genetic defect.  In males, there is no second X gene and the genetic defect is unopposed.  Affected males inherit this abnormal gene from their mothers, who are usually asymptomatic.  However, these males, the disease is more severe. 
    • In rare cases when females have the defective gene on both X chromosomes, the disease is equally severe.  Most commonly, however, women act as a "carrier" of the gene.  These women have variable expressions of the disease from no symptoms to moderate symptoms if under a significant degree of stimulation.  Most mutations identified are classified according to the following scheme: 
      • Class I - severe enzyme deficiency with chronic non-spherocytic hemolytic anemia
      • Class II - severe enzyme deficiency with <10% normal activity
      • Class III - mild to moderate enzyme deficiency (10%-60% normal activity)
      • Class IV - very mild to almost normal enzyme activity (>60% normal activity with no clinical consequences) 
    • In the United States, G6PD is found mainly in African Americans.  About 10% to 15% of that population is affected by the disease.  Also, those of Mediterranean descent (Italians, Greeks, Sephardic Jews) are at risk for the genetic defect. 

    Drug-Lab Interactions
    • With the dye reduction and glutathione screening testing, reticulocytosis associated with a hemolytic episode may be associated with falsely high levels of G6PD. 
    • Drugs that precipitate hemolysis in G6PD-deficient patients:  acetanilide, antimalarials, antipyretics, ascorbic acid, aspirin, dapsone, methylene blue, nalidixic acid, nitrofurantoin, phenacetin, phenazopyridine, primaquine, quinidine, sulfa, sulfonamides, thiazide diuretics, tolbutamide, Vitamin K (water soluble).
    Test Tube Needed
    • Lavender or green top tube
    • Perform a glucose-6-phosphate dehydrogenase screen prior to test.
    • Collect 5 mL of whole blood. 
    • Avoid hemolysis. 
    • Apply pressure or a pressure dressing to the venipuncture site and assess the site for bleeding. 
    • If the test indicates a G6PD deficiency, give the patient a list of drugs that may precipitate hemolysis.  Instruct patients with the Mediterranean type of this disease not to eat fava beans.  Teach patients to read labels on any over-the-counter (OTC) drugs for the presence of agents (e.g., aspirin, phenacetin) that may cause hemolytic anemia.
    What To Tell Patient Before & After
    • Explain the procedure to the patient.
    • Tell the patient that no fasting is required.
    • LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
    • Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.

MESH Terms & Keywords

  • Glucose, 6-Phosphate, Dehydrogenase, G6PD Level