G6PD Test (Glucose-6-Phosphate Dehydrogenase Enzyme Test)

Key takeaways

• The G6PD test identifies enzyme deficiency; the G6PD test does not predict when or whether haemolysis will happen.
• Testing during or just after an acute haemolytic episode can give a falsely normal result, because the surviving red cells are young and enzyme-rich.
• Female carriers can have near-normal enzyme activity on testing yet still be at some risk; a normal value in a girl or woman does not fully exclude deficiency.
• The G6PD test is not a test for anaemia, a full blood count, reticulocyte count and bilirubin are needed to assess haemolysis.
• Knowing G6PD status before starting primaquine, tafenoquine, dapsone, rasburicase or nitrofurantoin changes prescribing decisions.

At a glance

Also known as

• G6PD enzyme test, G6PD level, G6PD activity assay
• Glucose-6-phosphate dehydrogenase quantitative assay
• G6PD screening test (qualitative fluorescent spot test)
• Commonly asked for in India as "G6PD blood test", "jaundice enzyme test in newborn", or before anti-malarial treatment

What the G6PD test is

G6PD is an enzyme that keeps red blood cells supplied with a protective molecule (NADPH) that neutralises oxidative stress. When G6PD activity is low, oxidant stress from certain drugs, infections, or fava beans can damage haemoglobin and rupture red cells, producing sudden anaemia, dark urine and jaundice.

Two broad formats exist and they are not interchangeable:

• Quantitative enzyme assay (spectrophotometric): reports a numerical activity value. Preferred for diagnosis, and the only format that can give useful information in females and in borderline cases.
• Qualitative screening tests (fluorescent spot test, rapid point-of-care kits): give a normal/deficient or intermediate answer. Useful for screening large numbers or before anti-malarials, but these tests may miss partial deficiency and are poor at identifying heterozygous females.

Genetic testing for G6PD variants is a separate investigation, used mainly when enzyme results are inconclusive, in female relatives, or for family and genetic counselling.

Why the G6PD test is done

• To find the cause of unexplained haemolytic anaemia, especially after a new medicine, an infection or fava bean ingestion.
• To investigate significant or prolonged newborn jaundice, particularly when phototherapy or exchange transfusion is being considered.
• To check G6PD status before drugs known to cause haemolysis in deficient people, primaquine and tafenoquine for malaria, dapsone, rasburicase, nitrofurantoin, methylene blue and some sulphonamides.
• To test relatives after G6PD deficiency is diagnosed in the family.
• To explain recurrent episodes of dark (cola-coloured) urine with pallor.

Who should get this test

• Newborns with jaundice appearing early, rising quickly, needing phototherapy, or with a family history of neonatal jaundice or G6PD deficiency.
• Anyone about to receive primaquine, tafenoquine, dapsone or rasburicase: this is the single most practical reason for testing in India, given vivax malaria treatment.
• People with an acute haemolytic episode: sudden pallor, jaundice, dark urine, breathlessness, often 1-3 days after a trigger.
• Male relatives, sisters, mothers and daughters of a diagnosed person, because inheritance is X-linked.
• People from communities with higher prevalence, including several tribal populations in India, and those of Mediterranean, African, Middle Eastern or South-East Asian ancestry.
• Not required as a routine "general health check" add-on in someone with no symptoms, no family history and no planned oxidant drug, unless a doctor advises it.

What the G6PD test cannot detect or exclude

• It does not diagnose anaemia or haemolysis. The G6PD test says nothing about haemoglobin level, red cell destruction rate or bilirubin. A full blood count, reticulocyte count, peripheral smear, LDH and bilirubin are needed for that.
• It does not predict severity or timing. Many people with G6PD deficiency never have a haemolytic episode. Enzyme activity alone does not tell you how severely you will react to a given drug.
• It does not identify the genetic variant. Enzyme activity does not tell you whether you carry a Mediterranean, African A-, Mahidol, Orissa or other variant, which differ in severity.
• A normal result does not exclude deficiency if the sample was taken during or soon after an acute haemolytic episode, after a red cell transfusion, or in a female carrier with skewed X-inactivation.
• It does not exclude other causes of haemolysis: thalassaemia and other haemoglobinopathies, autoimmune haemolytic anaemia, hereditary spherocytosis, pyruvate kinase deficiency, malaria, sepsis or snake bite all need their own evaluation.
• It does not exclude other causes of neonatal jaundice such as ABO or Rh incompatibility, sepsis, hypothyroidism, or breast-milk jaundice.

A negative or normal finding describes what the assay measured on that sample, not what exists in every circumstance. If symptoms continue despite a normal G6PD result, return to your doctor for reassessment rather than assuming the question is settled.

Related but different examinations

These tests answer different questions. Which one comes first depends on the presentation: in a jaundiced newborn, bilirubin and blood group work come first; in an adult with cola-coloured urine after a new antibiotic, a full blood count and smear usually precede the G6PD assay; before prescribing primaquine, the G6PD test itself is the first step.

How to prepare

• Fasting: generally not needed for the G6PD test alone. If other tests are booked in the same visit, your unit's fasting instruction applies.
• Tell the laboratory about recent transfusion: transfused donor red cells can mask deficiency. Many units advise deferring the assay for a period after transfusion, follow the interval your treating team gives.
• Tell the doctor about a recent haemolytic episode: testing may need to be repeated weeks later for a reliable result.
• Medicines and supplements: list everything, including over-the-counter painkillers, antibiotics, anti-malarials, henna exposure, AYUSH or herbal preparations and gym supplements. Do not stop or change any prescribed medicine to prepare for this test, speak to the prescriber first.
• Current illness: mention fever or infection, as both can affect interpretation.
• Food avoidance: there is no need to avoid fava beans purely for the test. If you already know you are deficient, continue avoiding known triggers as advised by your doctor.

Preparation details, sample tube requirements, timing rules after transfusion and whether the quantitative or qualitative format is offered are operational decisions that differ between laboratories. Written instructions from the unit collecting your sample take precedence over any general guidance.

Newborns and infants

Sample is usually taken by heel prick or small venous draw. Cord blood or dried blood spot may be used in screening programmes. In a sick or jaundiced baby, testing is not delayed for fasting.

Pregnancy

The blood draw itself is unaffected by pregnancy. G6PD status may be checked if there is a family history, as it informs both maternal drug choices and newborn monitoring.

Children and older adults

No special preparation. In frail older adults with difficult veins, mention any bleeding tendency or anticoagulant use so pressure can be applied for longer.

People on multiple medicines

If you are on anti-tubercular therapy, anti-malarials, dapsone or sulphonamides, bring the prescription list. This information changes how the result is interpreted and what is safe to prescribe next.

What happens during the test

A trained phlebotomist cleans the skin, usually inside the elbow, and draws a small blood sample into an EDTA tube. In infants, a heel prick or fingerstick may be used. Pressure is applied for a minute or two afterwards.

How long the process takes: the collection itself takes about a minute; the whole visit, including registration and post-draw pressure, usually takes 5-10 minutes. Laboratory analysis time and report release vary by laboratory and by whether the assay is run in-house or sent to a reference laboratory, ask the unit issuing your report.

The sample must reach the laboratory in a controlled time and temperature window. If it does not, the laboratory may ask for a repeat draw; this is a sample-handling matter, not a sign of a problem with your health.

Understanding your report

Quantitative G6PD activity is usually reported in units per gram of haemoglobin, alongside that laboratory's own reference interval and, in some laboratories, as a percentage of the adjusted male median. Reference intervals and cut-offs differ between assay methods and laboratories, so compare your value only with the range printed on your own report, not with a value from a different laboratory or website.

• Activity within the laboratory's reference interval: significant deficiency is unlikely in a male, provided the sample was not taken during haemolysis or after transfusion. In a female, a normal value does not fully exclude carrier status.
• Clearly reduced activity: consistent with G6PD deficiency. This means trigger avoidance and careful prescribing, not that haemolysis is happening now.
• Intermediate or borderline activity: common in heterozygous females and in some variants. Usually needs repeat testing at a stable time, correlation with clinical history, and sometimes genotyping.
• Qualitative screen reported as "deficient" or "intermediate": normally confirmed with a quantitative assay before long-term labels or prescribing decisions are attached.

No result should be read in isolation. The doctor who requested the G6PD test will interpret it against your symptoms, blood counts, family history and current medicines. Results vary depending on individual clinical circumstances.

When results can be misleading

Falsely raised (falsely normal) activity

• During or soon after acute haemolysis: older, enzyme-poor cells have already been destroyed. The surviving young red cells and reticulocytes are rich in G6PD, so activity can appear normal even in a genuinely deficient person. This is the commonest cause of a missed diagnosis.
• After a recent red cell transfusion: donor cells with normal enzyme dilute the result.
• High reticulocyte count from any cause, including recovery from bleeding or iron therapy.
• Heterozygous females: a mixed red cell population can average out to a value inside the reference range while a susceptible subpopulation persists.

Falsely lowered activity

• Delayed, warm or badly handled samples: enzyme activity degrades with time and heat, which can falsely suggest deficiency.
• Clotted or under-filled tubes, or samples in the wrong anticoagulant.
• Severe anaemia with low haemoglobin, where normalisation of the value can be less reliable.

Other sources of confusion

• Different assay methods and different reference intervals make numbers from two laboratories non-comparable.
• Rapid point-of-care kits can report "normal" in partial deficiency.
• Where the clinical story strongly suggests G6PD deficiency but the assay is normal, repeat testing after full recovery, typically some weeks later, is usual practice.

Risks and safety

Venous blood draw

Risks are small and usually minor: brief pain, bruising, light-headedness or fainting, and rarely a small collection of blood under the skin (haematoma) or local infection. People on blood thinners or with bleeding disorders may bruise more and need longer pressure.

Heel prick or fingerstick in infants and children

Momentary pain, minor bruising and rarely local infection. Repeat pricks may be needed if the sample volume is inadequate.

Genetic testing, when done

The sample collection carries the same minor risks. The additional considerations are informational: results may have implications for siblings and future children, so genetic counselling is advisable. Report confidentiality is governed by applicable data-protection law, including the Digital Personal Data Protection Act 2023.

Special situations

Newborns

G6PD deficiency is an important cause of severe neonatal jaundice and, if untreated, of bilirubin-related brain injury. Testing is often prompted by early or rapidly rising jaundice. Newborn screening for G6PD is offered in some Indian hospitals and programmes but is not uniformly available nationwide.

Pregnancy and breastfeeding

Women who are G6PD deficient should have drug choices reviewed by the treating doctor. Some drugs taken by a breastfeeding mother, such as dapsone or nitrofurantoin in a very young or deficient baby, need specific advice, discuss with the prescriber rather than stopping treatment on your own.

Children

Episodes are often triggered by infection or by medicines bought without prescription. Keep a written list of triggers and show it at every consultation and pharmacy visit.

Malaria treatment

Radical cure of Plasmodium vivax uses primaquine or tafenoquine, both of which can cause haemolysis in G6PD deficiency. This is the main reason G6PD testing before treatment is emphasised in Indian malaria programmes. Dose and regimen decisions belong to the treating clinician.

Coexisting anaemia or haemoglobinopathy

Iron-deficiency anaemia and thalassaemia trait are both common in India and can coexist with G6PD deficiency, complicating interpretation of anaemia. Each needs its own investigation.

Older adults and people with kidney disease

Haemolysis places extra load on the kidneys; anyone with existing chronic kidney disease who develops dark urine should be assessed urgently rather than waiting.

The G6PD test in the Indian context

• Prevalence varies widely by region and community. Published Indian surveys report a broad range across states and among tribal populations, with higher frequencies in several tribal groups and specific variants such as G6PD Orissa and G6PD Mediterranean described in Indian cohorts. Because figures differ substantially between studies and sampling methods, family and community history matters more than any single national number.
• Vivax malaria makes the test practically important. India carries a substantial share of the world's P. vivax burden, and primaquine-based radical cure is where G6PD status directly changes prescribing.
• Self-medication is a real trigger. Antibiotics, anti-malarials and painkillers bought over the counter, plus some herbal, AYUSH and imported gym supplements, are recognised precipitants. Naphthalene mothballs and henna exposure have also been linked to haemolysis in deficient children.
• Terminology. Laboratories may list the test as "G6PD", "G-6-PD enzyme", "G6PD quantitative" or "G6PD screening". Ask which format was performed, it changes how confidently a normal result can be read.
• Availability. Quantitative assays are widely available in city laboratories; point-of-care kits are used in some field and programme settings. Genotyping is limited to specialised centres.

Cost and insurance in India

Costs differ considerably between cities, laboratory types and test formats. Rather than a fixed figure, it is more useful to know what moves the price:

• Test format: a qualitative screen generally costs less than a quantitative enzyme assay; G6PD genotyping costs substantially more.
• Laboratory type and city: government facilities, standalone laboratories and hospital-based NABL-accredited laboratories price differently.
• Bundling: G6PD is often ordered with a complete blood count, reticulocyte count, bilirubin and peripheral smear, which raises the total.
• Urgency and logistics: urgent processing, home collection and outstation sample transport to a reference laboratory add cost.
• Repeat testing: a confirmatory assay after recovery from haemolysis is a second charge.

Insurance: outpatient diagnostic tests are often not covered unless the policy includes an OPD or diagnostic benefit. When the G6PD test is part of an admission, for example a jaundiced newborn or an inpatient haemolytic episode, it is more commonly reimbursed within the hospitalisation claim. Check the current price and coverage with the laboratory and your insurer before testing.

Myths and facts

Frequently asked questions

Does the G6PD test need fasting?

No, the G6PD test alone does not usually require fasting. If your doctor has ordered other tests in the same visit, such as blood sugar or a lipid profile, those tests may need fasting. Follow the written instruction from the laboratory collecting your sample, as protocols differ between units.

Can the G6PD test be done during an episode of jaundice or dark urine?

Blood can be taken, but interpretation is limited. During haemolysis, enzyme-poor older red cells have been destroyed and the remaining young cells carry more G6PD, so activity can look normal. Doctors commonly repeat the assay several weeks after full recovery to confirm or exclude deficiency.

How is the G6PD test different from a complete blood count?

A complete blood count measures haemoglobin, red cells, white cells and platelets, showing whether anaemia is present. The G6PD test measures one enzyme's activity, showing whether a susceptibility exists. The two tests answer different questions and are frequently ordered together when haemolysis is suspected.

My daughter's G6PD result is normal. Can she still be a carrier?

Yes. In female carriers, red cells are a mixture of enzyme-normal and enzyme-deficient populations, and the averaged result can fall within the reference range. If there is a clear family history, discuss repeat quantitative testing or genetic testing with a haematologist or genetic counsellor.

Which medicines should be avoided in G6PD deficiency?

Drugs most consistently implicated include primaquine, tafenoquine, dapsone, rasburicase, nitrofurantoin, methylene blue and some sulphonamides. Risk depends on the drug, dose and G6PD variant. Show your report at every consultation and pharmacy visit, and never stop a prescribed medicine without speaking to the prescriber.

Is G6PD deficiency the same as thalassaemia?

No. G6PD deficiency is an enzyme defect that makes red cells vulnerable to oxidative stress. Thalassaemia is a disorder of haemoglobin production. Both are inherited and both are seen in India, they can coexist, and each requires its own test, enzyme assay versus haemoglobin electrophoresis or HPLC.

How long does the whole G6PD test process take?

Sample collection takes about a minute, and the visit usually about 5-10 minutes. Laboratory processing and report release depend on whether the assay is run in-house or referred out, so ask the laboratory issuing your report for its own timeline when you give the sample.

Should newborns be tested for G6PD deficiency routinely?

Newborn G6PD screening is offered in some Indian hospitals and programmes but is not universal. Testing is clearly indicated when jaundice appears early, rises quickly, needs phototherapy, or when there is a family history. Your paediatrician or neonatologist will advise based on the baby's clinical course.

Can a rapid point-of-care G6PD kit replace the laboratory assay?

Rapid kits are valuable where laboratory access is limited, particularly before anti-malarial treatment. However, these kits can miss partial deficiency and are unreliable in heterozygous females. A quantitative laboratory assay is generally used to confirm before a lifelong diagnostic label or prescribing restriction is applied.

Sources

• World Health Organization guidance on G6PD deficiency testing in the context of malaria radical cure, including WHO Guidelines for Malaria (latest edition) [Confirm current edition, TO BE VERIFIED]
• National Center for Vector Borne Diseases Control (NCVBDC), Ministry of Health and Family Welfare, India, national malaria treatment guidelines [Confirm current edition, TO BE VERIFIED]
• Indian Council of Medical Research publications on G6PD deficiency prevalence and variants in Indian populations [Confirm current edition, TO BE VERIFIED]
• American Academy of Pediatrics clinical practice guideline on management of hyperbilirubinaemia in the newborn [Confirm current edition, TO BE VERIFIED]
• Digital Personal Data Protection Act, 2023 (Government of India), handling of health data and reports