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Blood Test Tracker

G6PD (Glucose-6-Phosphate Dehydrogenase)

Measures how active the G6PD enzyme is in your red blood cells. Low activity is called G6PD deficiency.

AI-verified against cited sources. Awaiting expert reviewAlso called G6PD, G-6-PD, G6PDHLOINC 32546-4

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What it is

G6PD is an enzyme inside red blood cells that helps protect them from damage. The G6PD gene sits on the X chromosome, so low activity is passed down in families and is more common in males, though females can have it too. Most people with low activity feel well day to day. The test measures enzyme activity in a whole-blood sample and reports it per gram of hemoglobin (U/g Hb). Labs compare your result with their own range, and some also give cut-offs as a percent of normal.

Why it matters

In G6PD deficiency, red blood cells can break down quickly (hemolysis) after certain triggers, such as some medicines, fava beans or an infection. This can cause tiredness, yellow skin or eyes, and dark urine. Knowing your status helps clinicians and pharmacists choose medicines with care. G6PD deficiency is also linked to a higher chance of newborn jaundice. Almost 5 in 100 people worldwide have it, and it is more common in people with ancestry from Africa, the Mediterranean, the Middle East and Asia.

If it’s low

A low result means the G6PD enzyme is less active than usual. In males, a clearly low result is usually a sign of G6PD deficiency. In females, who carry two X chromosomes, activity can fall anywhere between normal and deficient, and a middle result is called intermediate. WHO guidance treats activity under 30% of the normal median as deficient. How much it matters depends on the specific gene change and on what triggers it.

Common causes

  • An inherited G6PD gene change, which is the usual cause
  • In females, carrying one changed copy of the gene, which often gives intermediate activity
  • Rarely, a gene change that causes ongoing red cell breakdown even without a trigger

What can help

  • Share your result with every clinician and pharmacist, and ask them to check any new medicine against your G6PD status
  • Ask your clinician about fava beans and other known triggers
  • Ask whether family members should be tested, since G6PD deficiency is inherited

If it’s high

A result above your lab's range is usually not a health concern. The most common reason is a large number of young red cells, which have more G6PD than older cells. This can follow bleeding or red cell breakdown. Babies also normally have higher activity. Because red cell breakdown can also make a deficient person's result look normal, your clinician may suggest a repeat test later.

Common causes

  • A recent period of red cell breakdown or blood loss, when young red cells fill the blood
  • Being a newborn or young infant
  • A lab method or range that runs higher than another lab's

What can help

  • If you were recently ill, bleeding or transfused, ask whether the test should be repeated once things have settled

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 5 ranges

See G6PD by age and sex, with the U.S. survey numbers where they exist.

WHO 2018 activity categories as applied by ARUP (females, age 18 and over)

  • Deficient (under 30% of the normal median)below 3.8 U/g Hb
  • Intermediate (30% to under 80% of the normal median)3.8 to under 10.2 U/g Hb
  • Normal (80% of the normal median or higher)10.2 and above U/g Hb

WHO 2018 activity categories as applied by ARUP (males, age 18 and over)

  • Deficient (under 30% of the normal median)below 3.8 U/g Hb
  • Normal (30% of the normal median or higher)3.8 and above U/g Hb

If this applies to you

G6PD means a little more for some people. Open the one that fits you.

Gout

Pegloticase is an infused gout medicine. Its FDA label calls for checking people at risk of G6PD deficiency before starting, since that risk is higher with African, Mediterranean or Southern Asian ancestry, and it is not used in people who have the deficiency.

Blood tests for gout

What can affect your result

  • Age: newborns have higher activity than older children and adults
  • Sex and X-linked inheritance: females who carry one changed copy can have normal, intermediate or low activity
  • Recent red cell breakdown or a recent transfusion, which can make a deficiency look normal
  • Anemia, acute leukemia and unusual white cell or platelet counts, which can make the activity less reliable
  • The lab's method, test temperature and range: numbers from different labs are not interchangeable
  • Ancestry: the gene changes that cause deficiency are more common in some populations
  • A recent blood transfusion can hide a deficiency, because the donor red cells usually have normal G6PD.
  • Recent red cell breakdown can make a deficient person's result look normal. Young red cells (reticulocytes) hold more G6PD than old ones, and a test done during or soon after a hemolytic episode can be falsely normal.
  • Anemia, acute leukemia and unusual white cell or platelet counts can make the activity less reliable. G6PD activity rises and falls with the white cell and platelet counts.
  • Newborns have higher activity than older children and adults, so adult ranges do not fit them.
  • In females, activity can land anywhere from normal to deficient because each cell uses only one of the two X chromosomes.
  • Results depend on the lab's method and test temperature, and cut-offs are not interchangeable between labs.
  • Clotted, frozen or hemolyzed samples are rejected by ARUP. Acid citrate dextrose (yellow top) is the preferred tube, and the sample is kept refrigerated.

G6PD status is inherited and does not change over time. Measured activity can look temporarily higher after red cell breakdown or a transfusion.

When to talk to a clinician

If you know you have low G6PD activity, get prompt care for dark, red-brown or cola-colored urine, yellow skin or eyes, back or belly pain, unusual paleness, a racing heart or shortness of breath, especially in the days after a new medicine, an infection or eating fava beans. Red cell breakdown from a medicine usually starts 24 to 72 hours after taking it. Call 911 or your local emergency number for chest pain, fainting, confusion or severe trouble breathing. For a newborn with yellow skin or eyes in the first days of life, contact the baby's clinician promptly.

Questions you could ask

  • Is my result a screen or a measured number, and how does my lab sort results into normal, intermediate and deficient?
  • Could a recent illness, bleeding or transfusion have affected this result, and should we repeat it?
  • What does my result mean for medicines I might need in the future?
  • Should family members be tested?
  • Would a repeat test or a gene test help confirm this?

Questions people ask

My G6PD result is normal, but I was told I might still be deficient. How is that possible?

Two situations can hide a deficiency. A test done soon after red cell breakdown or a transfusion can look normal, because young red cells and donor cells have normal activity. And a female who carries one changed copy can have a mix of normal and low cells, so the average can land in the normal range. If your clinician still suspects a deficiency, they may repeat the test later or suggest gene testing.

Why do the cut-offs differ between labs?

Each lab's method, equipment and test temperature give different numbers for the same blood. ARUP states that its cut-offs apply only to its own assay, and one lab's normal range can sit lower than another's. Use the range and categories printed on your own report.

Does a low result mean I have to avoid certain foods or medicines?

It means some triggers matter more for you. Fava beans are a well-known food trigger, and some medicines can cause red cell breakdown in G6PD deficiency. Risk differs by medicine, and many commonly warned-about drugs have little evidence of harm, so ask your clinician or pharmacist to check each medicine instead of relying on a general list.

Show the science and sources

For clinicians and researchers

Quantitative assays measure NADPH production spectrophotometrically (Mayo: kinetic spectrophotometry; ARUP: quantitative enzymatic assay) and normalize to hemoglobin (U/g Hb). Some methods normalize to red cell count and use other units, which cannot be converted without the hemoglobin or red cell count. Acid citrate dextrose preserves the enzyme best (ARUP). Intervals are method-specific: ARUP 9.6–16.3 U/g Hb for adults (16.4–24.1 for newborns under 8 days, falling to 9.7–16.9 for 1 to 17 years) versus Mayo 8.0–11.9 U/g Hb from 12 months. ARUP applies WHO 2018 guidance: 100% is the median of non-affected males (12.7 U/g Hb at 18 and over), males below 30% (3.8) are deficient, and females below 30% are deficient, 30% to under 80% (3.8 to 10.2) intermediate and 80% or more normal. These cut-offs are assay-specific. WHO historically grouped variants into classes I to IV by residual activity and clinical picture. A 2022 WHO working group proposed four classes: A (under 20% activity, chronic hemolysis), B (under 45%, acute triggered hemolysis), C (60% to 150%, no hemolysis) and U (uncertain). Genotype cannot predict the phenotype of heterozygous females because of X-inactivation mosaicism, so activity testing is needed (CPIC 2023). Hemolysis typically follows drug exposure after 24 to 72 hours and resolves within 4 to 7 days even if exposure continues, because older, more deficient cells are lost first (AAFP 2005). The reticulocyte count rises about 4 to 7 days after hemolysis, and testing during acute hemolysis can be falsely normal because the oldest, most deficient cells are lost first and young cells have near-normal activity. G6PD activity correlates positively with leukocyte and platelet counts and corrections are not standardized. Triggers include certain drugs (for example primaquine and rasburicase), fava beans and infection (Luzzatto 2020). CPIC 2023 rates medicines as high, medium or low risk and notes that many warnings rest on sparse evidence. No critical value was found.

LOINC 32546-4 (primary), 2357-2, 71593-8. Specimen: whole-blood.

Sources

  1. Glucose-6-Phosphate Dehydrogenase (test 0080135), ARUP Laboratories
  2. Glucose 6-Phosphate Dehydrogenase Enzyme Activity, Blood (test G6PD1), Mayo Clinic Laboratories
  3. Guide to G6PD deficiency rapid diagnostic testing to support P. vivax radical cure, World Health Organization (2018)
  4. Expanded Clinical Pharmacogenetics Implementation Consortium Guideline for Medication Use in the Context of G6PD Genotype, Clinical Pharmacology & Therapeutics (2023)
  5. Diagnosis and management of G6PD deficiency, American Family Physician (2005)
  6. Glucose-6-phosphate dehydrogenase deficiency, Blood (2020)
  7. G6PD Quantitative (lab code G6PDR), UW Medicine Laboratory Medicine

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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