🧬 G6PD Test: Complete Guide to Deficiency Diagnosis and Hemolysis Risk Assessment

G6PD (Glucose-6-Phosphate Dehydrogenase) deficiency is the most common inherited red blood cell enzyme disorder worldwide and a major cause of oxidative hemolysis. The G6PD test is essential for evaluating unexplained hemolytic anemia, neonatal jaundice, and drug-induced hemolysis risk—especially before prescribing oxidant medications.

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🔬 What Is G6PD?

Glucose-6-phosphate dehydrogenase is a key enzyme in the pentose phosphate pathway.
Its main role is:

• Producing NADPH
• Protecting red blood cells from oxidative damage
• Preventing hemoglobin denaturation (Heinz body formation)
• Maintaining RBC membrane stability

When G6PD is deficient, RBCs become extremely vulnerable to oxidative stress, leading to acute or chronic hemolytic anemia.

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🎯 Purpose of the G6PD Test

1) Diagnose congenital G6PD deficiency

• Identify enzyme deficiency
• Evaluate family history
• Detect female carriers (X-linked trait)

2) Prevent drug-induced hemolysis

Must be checked before giving oxidant medications:

• Primaquine
• Dapsone
• Nitrofurantoin
• Sulfonamides
• Rasburicase

3) Evaluate neonatal jaundice

Unexplained indirect hyperbilirubinemia can indicate G6PD deficiency.

4) Assess acute hemolytic episodes

Triggered by:

• Infection
• Drugs
• Foods such as fava beans (favism)

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🔬 G6PD Testing Methods

1) Electrochemical Assay (Modern method, POCT-friendly)

Principle:
Measures NADPH generated by G6PD based on electrochemical oxidation–reduction signals.

Advantages:

• Requires only a small blood volume
• Fast turnaround time
• Suitable for neonatal screening
• Useful in point-of-care settings

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2) UV Spectrophotometric Assay (Gold Standard)

Measures increased absorbance of NADPH at 340 nm.

Strengths:

• Most accurate quantitative method
• Standard reference in clinical laboratories

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3) Fluorescent Spot Test

Qualitative screening test for newborns.
Checks for fluorescence under UV light → Normal vs deficient.

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4) Genetic Testing

Identifies specific G6PD gene mutations.
Useful for carrier detection and confirmatory diagnosis.

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📊 Reference Range

(Varies by instrument and method—always follow your laboratory’s range.)

Group	Reference Value
Adult males	≥ 2.19 U/g Hb
Adult females	≥ 5.83 U/g Hb

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🧑‍⚕️ Clinical Significance

🔺 Increased G6PD Activity

Not clinically meaningful in most cases. Seen in:

• Reticulocytosis
• Samples with high WBC counts
• Certain bone marrow recovery states (e.g., pernicious anemia)

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🔻 Decreased G6PD Activity (Clinically significant)

1) Congenital G6PD Deficiency

• X-linked recessive inheritance
• Common in Asia, Mediterranean regions, Africa
• Causes episodic or chronic hemolysis

2) Drug-induced hemolysis

Triggered by:

• Primaquine
• Dapsone
• Nitrofurantoin
• Rasburicase
• Sulfonamide antibiotics

3) Infection-related hemolysis

Oxidative stress during infection can precipitate acute hemolysis.

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🔍 Interpretation Tips & Pitfalls

⚠ 1) False-negative during acute hemolysis

Old RBCs (low G6PD) are destroyed → younger RBCs (high G6PD) dominate.
→ Retesting 2–3 months later is recommended.

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⚠ 2) False-normal after blood transfusion

Transfused normal donor RBCs can mask deficiency.
→ Test at least 3 months after transfusion.

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⚠ 3) Female carriers can appear normal

Due to X-chromosome inactivation (mosaicism).
→ Combine quantitative assay + genetic testing if needed.

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⚠ 4) Leukocytosis can falsely elevate results

WBCs contain G6PD → may overestimate enzyme activity.

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📚 References

• WHO Working Group. G6PD Deficiency.
• Cappellini MD, Fiorelli G. G6PD Deficiency. Lancet.
• Beutler E. G6PD Deficiency: Historical Perspective. Blood.
• NCCLS Guidelines for Quantitative G6PD Assay.
• Luzzatto L, et al. Hemolytic Syndromes in G6PD Deficiency.
• Roper D, et al. G6PD Testing Methodologies. Clin Biochem.