G6PD Deficiency Diagnosis and Management

Assay Selection and Interpretation

A G6PD assay is generally sufficient for diagnosing G6PD deficiency in most patients, but the type of assay matters significantly—qualitative tests work well for males and homozygous females with severe deficiency, while quantitative assays or flow cytometry are necessary for heterozygous females and patients with concurrent hematological conditions 1
Qualitative fluorescent spot tests are appropriate for detecting severe G6PD deficiency (enzyme activity <10% of normal) in males and homozygous females 1

Avoid testing during or immediately after acute hemolytic episodes, as reticulocytes and young RBCs may contain near-normal enzyme levels, potentially masking deficiency 2
Wait at least 50 days after RBC transfusion before performing enzyme assays, as donor RBC contamination of 6-12% can cause false-negative results 2
Testing 120 days post-transfusion is ideal but often impractical in frequently transfused patients 2
Consider calculating the PK/G6PD ratio or comparing to controls with similar reticulocyte counts when interpreting borderline results 2

Qualitative screening is recommended before starting oxidant drugs (dapsone, primaquine, sulfonamides) in patients of Mediterranean, African, Indian, or Southeast Asian descent 1
For P. vivax radical cure with tafenoquine, quantitative G6PD testing is required—do not use if activity is <70% 1
Primaquine, rasburicase, and methylene blue are absolutely contraindicated in G6PD deficiency 1, 3

Molecular analysis may be required in females heterozygous for the disorder when enzymatic testing is inconclusive 1, 3
Genetic testing helps identify specific variants (Mediterranean vs. African), which determines hemolytic risk severity and drug contraindications 1, 3
The Mediterranean variant (Gdmed) causes life-threatening hemolysis requiring strict oxidant drug avoidance, while the African variant (GdA-) produces milder, self-limited hemolysis 1, 3
Quantitative testing is needed to determine the degree of deficiency in borderline cases, particularly when considering weekly primaquine dosing 3
Patients with 30-70% activity and non-Mediterranean variants can receive modified primaquine regimens with close monitoring 1
Neutropenia may be present but is not a reliable screening marker for G6PD deficiency 1
Testing whole blood without removing white cells and platelets prevents detection of deficiency in all cases examined 2
Buffy coat removal or filtration is essential for accurate RBC enzyme measurement 2

The American College of Physicians recommends calculating the percentage of normal G6PD activity by dividing the patient's G6PD level by the laboratory upper limit of normal and multiplying by 100, to determine the risk of hemolysis with dapsone therapy 4

The American Academy of Dermatology suggests using alternative immunosuppressants such as mycophenolate, azathioprine, or methotrexate for dermatologic conditions in patients with G6PD deficiency 5
The American Academy of Ophthalmology recommends using atovaquone or inhaled pentamidine for Pneumocystis prophylaxis in patients with G6PD deficiency 6

The American Society of Hematology recommends immediately discontinuing dapsone and using ascorbic acid as an alternative treatment for methemoglobinemia in G6PD-deficient patients 7
The American Society of Hematology suggests considering exchange transfusion for severe cases of hemolysis and monitoring for rebound methemoglobinemia requiring repeat dosing every 6-8 hours for up to 2-3 days after dapsone exposure 7
The American Society of Hematology recommends screening first-degree relatives of G6PD-deficient patients and screening before initiating any oxidant drugs in patients of Mediterranean, African, Indian, or Southeast Asian descent 8

The Infectious Diseases Society of America recommends screening before initiating any oxidant drugs in patients of Mediterranean, African, Indian, or Southeast Asian descent 4

Infants with rapidly rising total serum bilirubin (TSB) approaching exchange transfusion levels or not responding to phototherapy require quantitative G6PD testing as part of the evaluation, according to the American Academy of Pediatrics 9
Quantitative G6PD testing is recommended for infants receiving phototherapy with TSB rising rapidly and crossing percentiles unexpectedly, as stated by the American Academy of Pediatrics 9
For infants with jaundice in the first 24 hours or excessive jaundice for age, measuring G6PD as part of the laboratory evaluation is suggested by the American Academy of Pediatrics 9

Quantitative G6PD should be measured when TSB is approaching exchange levels, as recommended by the American Academy of Pediatrics 9
G6PD testing should be considered when jaundice appears in the first 24 hours of life, according to the American Academy of Pediatrics 9
G6PD deficiency was identified as the cause in 31.5% of infants who developed kernicterus in one series, highlighting the importance of quantitative G6PD testing in this population, as reported by the American Academy of Pediatrics 9

Ascorbic acid is the treatment of choice for methemoglobinemia in G6PD-deficient patients when methylene blue is contraindicated, according to the American Journal of Hematology 10
The doses recommended for treating methemoglobinemia (0.5-10 g) exceed the FDA-mandated RDA limit for G6PD-deficient patients, creating a clinical dilemma where the benefit of treating life-threatening methemoglobinemia outweighs hemolysis risk 10
Exchange transfusion should be considered for severe cases of ascorbic acid-induced hemolysis in G6PD-deficient patients 10