A-202 Establishing WHO 2022 Normal Male Median–Based Reference Intervals for G6PD Activity in a Large Institutional Cohort

Abstract

Accurate diagnosis of glucose-6-phosphate dehydrogenase (G6PD) deficiency requires population-specific reference intervals, typically normalized to hemoglobin (U/g Hb) and interpreted relative to the normal male median (NMM), as recommended by the WHO 2022 guidelines (1). Static manufacturer-supplied ranges do not account for genetic diversity or age-related variability. To improve clinical interpretation in our diverse patient population, our laboratory transitioned from a fixed reference interval (7.9–16.3 U/g Hb) to NMM-based thresholds aligned with WHO guidance. G6PD activity was measured using the Pointe Scientific spectrophotometric assay on a Beckman AU5800 analyzer. We conducted a retrospective review of 7,723 patient specimens analyzed between October 2, 2022, and November 14, 2025. Data extracted included G6PD activity (U/g Hb), patient age, sex, ethnicity, collection details, and the history of G6PD deficiency. Results were stratified by demographic variables, and descriptive statistics were calculated, including mean, median, standard deviation, and 95% confidence intervals. Comparisons between adult males, the overall adult cohort, and the overall pediatric cohort were performed using Welch’s t-test. Of 7,723 specimens, 7,595 were adults (=18 years), including 4,243 adult males, and 123 were pediatric (<18 years). G6PD activity demonstrated a right-skewed distribution with a peak between 14–16 U/g Hb and an extended upper tail beyond 60 U/g Hb. Among adults, mean G6PD activity was 16.85 ± 7.77 U/g Hb (median 15.7; 95% CI 16.67–17.02). Adult males had a mean of 16.57 ± 7.97 U/g Hb (median 15.4; 95% CI 16.33–16.81). There was no statistically significant difference between the overall adult cohort and adult males (Welch’s t = 1.85, p = 0.065), supporting use of an adult-derived NMM for interpretation. Female participants demonstrated greater variability, consistent with heterozygous mosaic expression, though central tendency closely approximated the male distribution. Pediatric samples showed higher enzyme activity (mean 20.55 ± 9.69 U/g Hb; median 22.1; 95% CI 18.82–22.28). In this large institutional cohort, adult G6PD activity demonstrated a stable distribution with no significant difference between overall adult and male-only values, supporting adoption of an adult-derived NMM for interpretation (Table 1). Transitioning to WHO 2022 NMM-based thresholds enabled standardized severity classification and reduced potential misclassification associated with fixed manufacturer ranges. Implementation of an NMM-aligned reference framework enhances diagnostic clarity and harmonizes institutional reporting with contemporary international guidelines. References: 1. Luzzatto L, Bancone G, Dugué PA, et al. New WHO classification of genetic variants causing G6PD deficiency. Bull World Health Organ. 2024;102(8):615-617.