What this test measures
Glucose-6-Phosphate Dehydrogenase (G6PD) is the first enzyme of the pentose phosphate pathway in red blood cells. It is essential for generating NADPH, which keeps glutathione reduced and protects haemoglobin from oxidative damage.
G6PD deficiency is the commonest enzyme deficiency in humans — X-linked, affecting men more severely than women. The deficiency is asymptomatic at baseline but causes acute haemolytic anaemia when the red cells are exposed to oxidative stress: certain drugs (primaquine, dapsone, sulphonamides, nitrofurantoin, methylene blue, rasburicase), fava beans, and severe infection.
Why it matters
G6PD deficiency is particularly common in parts of India — 1–10% of males in many communities (highest in some tribal and Mediterranean-origin populations). It matters because:
• Malaria treatment with primaquine (radical cure) can cause severe haemolysis in deficient patients — testing is recommended before treatment. • Many common drugs (dapsone for leprosy and PCP prophylaxis, nitrofurantoin for UTI, sulphonamides) cause haemolysis. • Neonates with G6PD deficiency are at higher risk of severe neonatal jaundice and kernicterus — many Indian newborn screening programmes now include G6PD. • Fava bean ingestion (Mediterranean-origin variant) causes "favism" — sudden severe haemolysis.
A G6PD test is recommended before starting any of the haemolysis-inducing drugs, in any newborn with prolonged or severe jaundice, and in family screening once an index case is identified.
How to prepare
No fasting required. Critically — do NOT test immediately after a haemolytic episode. Young red cells (reticulocytes) have higher G6PD levels than older cells, so right after haemolysis the surviving young cells can produce a falsely normal result. Wait 2–3 months after acute haemolysis. Continue medications unless your doctor instructs otherwise.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| G6PD (U/g Hb)[1][2] | Adult: 6.4 – 18.7 U/g Hb (quantitative); WHO Class III: < 60% of normal; severe (Class I/II): < 10% | Reduced G6PD activity confirms deficiency. WHO classifies it I (severe chronic non-spherocytic haemolytic anaemia), II (severe, < 10%, drug-induced episodes), III (moderate, 10–60%, common Mediterranean / African / Indian variants), IV (mild < 60–100%), V (no haemolysis). Most Indian cases are Class III. | Normal or high G6PD usually rules out deficiency. False normal results can occur shortly after a haemolytic episode (young reticulocytes have high enzyme) — retest in 2–3 months if clinically suspected. |
G6PD activity and clinical risk
| G6PD activity | WHO Class | Clinical picture |
|---|---|---|
| < 1% normal | Class I | Chronic non-spherocytic haemolytic anaemia |
| < 10% normal | Class II | Severe — drug-induced acute haemolysis (Mediterranean variant) |
| 10 – 60% normal | Class III | Moderate — most Indian and African variants; episodes triggered by drugs / infection |
| 60 – 100% normal | Class IV | Mild — no clinical haemolysis |
| Normal | Class V | No deficiency |
Frequently asked questions
Why might my doctor want this before starting an antimalarial?
Primaquine and tafenoquine — used for radical cure of Plasmodium vivax — can cause severe haemolysis in G6PD-deficient patients. WHO and Indian national malaria guidelines recommend G6PD testing before these drugs.
Is G6PD deficiency hereditary?
Yes — X-linked. Men are usually fully deficient if they carry the gene; women can be carriers (less affected) or fully deficient if both X chromosomes carry the gene. Family screening is recommended once an index case is identified.
I have G6PD deficiency — which drugs should I avoid?
Primaquine, dapsone, nitrofurantoin, sulphonamides, methylene blue, rasburicase, naphthalene mothballs, and high-dose vitamin C and aspirin. Carry a list of unsafe medications and tell every doctor and chemist.
What about fava beans?
People with the Mediterranean variant of G6PD deficiency can have severe haemolysis after eating fava beans ("favism"). Most Indian variants do not have this dramatic response, but caution is reasonable.
Is the test affected by recent haemolysis?
Yes — and falsely so. After haemolysis, only young red cells (with relatively high G6PD) survive, giving a falsely normal result. Wait 2–3 months after an acute episode before testing.
Should newborns be tested?
Newborns with severe or prolonged jaundice should be tested — G6PD deficiency is a treatable cause and family counselling is important. Some Indian newborn screening programmes now include G6PD.
Can I live a normal life with G6PD deficiency?
Yes — between triggers, G6PD-deficient people are completely well. Avoiding the trigger drugs, foods (fava beans for Mediterranean variant) and treating infections promptly is enough for almost all.
Related Diabetes / Glucose tests
Tests commonly ordered alongside GLUCOSE-6-PHOSPHATE DEHYDROGENASE, or that help interpret an unexpected result.
Sources & references
- American Society of Hematology — G6PD Deficiency · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — G6PD Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — G6PD Deficiency · accessed 2026-05-30T00:00:00.000Z
- WHO — Guide to G6PD Deficiency Rapid Diagnostic Testing · accessed 2026-05-30T00:00:00.000Z
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