G-6-PD Quantitative Test

G-6-PD Quantitative Test: Detecting Enzyme Deficiency & Hemolysis Causes

G-6-PD Quantitative Test

Synonyms

G-6-PD, Quantitative, Blood

Applies to

Heinz Bodies

Specimen

Erythrocytes

Container

• Lavender top (EDTA) tube
• Green top (heparin) tube
• Acid-citrate-dextrose (ACD) solution tube

Storage Instructions

• Stable at 4°C for up to 6 days
• Stable at 25°C for at least 24 hours
• Ship on wet ice if sending to referral lab (do not freeze)

Reference Range

8.34 ± 1.59 IU/g hemoglobin

Use

This test is used to:

• Identify glucose-6-phosphate dehydrogenase (G-6-PD) deficiency
• Determine cause of drug-induced hemolysis
• Investigate hemolysis due to bacterial/viral infection
• Evaluate hemolysis related to metabolic disorders such as acidosis

Limitations

A false-normal result may occur after acute hemolysis. After hemolytic episodes, younger red cells and reticulocytes (which have higher G-6-PD activity) dominate, potentially masking deficiency.

Contraindications

• Normal G-6-PD screen
• Marked reticulocytosis

Methodology

The test quantifies NADPH formation by measuring change in absorbance at 340 nm at 37°C using patient hemolysate. The rate of NADP+ reduction to NADPH reflects G-6-PD activity.

Additional Information

• Screening should precede the quantitative test.
• Heinz bodies may be observed in peripheral smears during G-6-PD-related hemolysis.
• Older erythrocytes have the lowest G-6-PD levels and are destroyed first in hemolytic crises.
• Reticulocytes and younger red cells exhibit higher enzyme levels—thus post-crisis levels may appear falsely normal.
• Quantitative testing is especially useful in:
  • Female patients (carrier state)
  • Mild G-6-PD deficient males post-hemolysis
• Consider reticulocyte-poor red cell fractions for more accurate diagnosis.
• Molecular techniques (e.g., mutation detection) are available for confirming G-6-PD deficiency.

References

1. Beutler E. “Study of Glucose-6-Phosphate Dehydrogenase: History and Molecular Biology.” Am J Hematol. 1993; 42(1):53-8.
2. Dacie J. *The Haemolytic Anaemias*, 3rd ed, Vol 1, Part 1, Chapter 9. Churchill Livingstone, 1985.
3. Mentzer WC, Wagner GM. *The Hereditary Haemolytic Anaemias*. Churchill Livingstone, 1989.
4. Williams WJ, Beutler E, Erslev AJ, et al. *Hematology*, 4th ed. McGraw-Hill, 1990.
5. Jacobs et al. *Laboratory Test Handbook*. Lexi-Comp Inc, 1994.