Overview
G6PD testing measures erythrocyte enzyme activity that protects RBCs from oxidative injury via the pentose phosphate pathway.
Clinical Importance
Before using certain oxidant drugs (e.g., selected 8-aminoquinolines) per WHO and clinical guidance
In evaluation of acute non-immune hemolysis
Specimen Requirements
- Specimen: whole blood
- Tube: lavender-top K₂EDTA (preferred) or K₃EDTA
- Anticoagulant: EDTA
- Avoid testing during/immediately after acute hemolytic episode when possible; young reticulocytes may yield falsely near-normal activity
- Follow quantitative vs qualitative method storage requirements
Analytical Method
Qualitative fluorescent spot or dye-decolorization screens detect NADPH generation. Quantitative spectrophotometric assays measure enzyme activity in IU/g Hb. Point-of-care tests exist for selected settings (WHO guidance).
Instruments Used
Automated analyzers
- Spectrophotometers / chemistry modules configured for quantitative G6PD activity
- Validated point-of-care G6PD devices in selected programs
Manual methods
- Fluorescent spot test and other qualitative screens
Reference Values
Typical adult SI examples below follow widely published international hematology practice (e.g., Dacie and Lewis; Henry's). Always interpret against the method- and demographics-specific interval printed on the patient report (CLSI EP28-A3c). Neonatal, pediatric, pregnancy, and altitude intervals differ.
Quantitative activity units and cutoffs are method-specific (often expressed as IU/g Hb).
WHO classification frameworks describe deficiency severity categories; apply the performing laboratory's interpretive criteria.
Interpretation
Common Causes of Increased Results
- Elevated activity may accompany reticulocytosis; not a clinical target
Common Causes of Decreased Results
- Reduced activity indicates G6PD deficiency; classify severity per method/WHO-aligned criteria
Clinical Significance
- Pre-drug safety screening
- Workup of oxidant-triggered hemolysis
Factors Affecting Results
Pre-analytical
- Testing during acute hemolysis/reticulocytosis causing false near-normal results
- Recent transfusion diluting deficient cells with donor RBCs
Analytical
- Incomplete leukocyte removal in some methods
- Assay temperature and reagent integrity
Post-analytical
- Reporting a 'normal' screen without noting timing relative to hemolysis
Advantages and Limitations
Advantages
- Prevents avoidable drug-induced hemolysis when used correctly
Limitations
- False normal results after acute hemolysis
- Qualitative screens may miss some heterozygous females
Clinical Pearls
If clinical suspicion for G6PD deficiency is high but the acute-phase screen is normal, repeat quantitative testing after the reticulocyte surge settles.
References
Authoritative textbooks, guidelines, and reviews supporting this laboratory test reference. Verify reference intervals, critical limits, and method details against institutional protocols and current guideline editions.
Textbooks
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Rodak BF, Carr JH. Rodak's Hematology: Clinical Principles and Applications. 6th ed. Elsevier; 2020.
- Hoffbrand AV, Moss PAH, Pettit JE. Essential Haematology. 8th ed. Wiley-Blackwell; 2019.
- McKenzie SB, Williams JL. Clinical Laboratory Hematology. 4th ed. Pearson; 2022.
- Bain BJ, Bates I, Laffan MA. Dacie and Lewis Practical Haematology. 12th ed. Elsevier; 2017.
- Kaushansky K, et al. Williams Hematology. 10th ed. McGraw-Hill; 2021.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
- Clinical and Laboratory Standards Institute. Management of Critical- and Significant-Risk Results. CLSI guideline GP47-Ed1. CLSI; 2015.
WHO Publications
- World Health Organization. Guide to G6PD testing and counselling for safe use of 8-aminoquinoline drugs. WHO; 2022.
- World Health Organization. Guide to G6PD testing and counselling for safe use of 8-aminoquinoline drugs. WHO; 2022.
Frequently Asked Questions
Common questions about using this G6PD Screening laboratory test Medical Laboratory Library reference in Medical Laboratory Science education.
What is the G6PD Screening laboratory test reference used for?
This Medical Laboratory Library page summarizes the clinical importance of G6PD Screening. Review the Clinical Importance section for why the test is ordered in laboratory medicine practice.
Where can I find G6PD Screening specimen requirements?
See the Specimen Requirements section on this page for specimen information related to G6PD Screening. Confirm collection details against your laboratory protocol.
Where are G6PD Screening reference values listed?
See the Reference Values section on this Laboratory Library page. Reference ranges can vary by method and population, so verify intervals with your laboratory.
How do I interpret G6PD Screening results?
Use the Interpretation section for laboratory interpretation framing, including increased and decreased result patterns when provided. Do not treat educational text as a patient-specific diagnosis.
What analytical method is used for G6PD Screening?
See the Analytical Method section for principle and method notes. Method details may differ by instrument and institutional SOP.
Are related laboratory tests linked from G6PD Screening?
Yes. The Related Laboratory Tests section lists connected references for continued lookup in the Medical Laboratory Library.
How can I continue learning after reading G6PD Screening?
Use Continue learning links on this page for related Academy lessons, medical laboratory quizzes, or laboratory case studies when available for this Hematology topic.
What are the clinical pearls for G6PD Screening?
See the Clinical Pearls section for concise laboratory practice notes associated with G6PD Screening. Apply pearls alongside institutional protocols.
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