Abstract
OBJECTIVE: To characterise quantitative glucose-6-phosphate dehydrogenase (G6PD) activity in term and preterm neonates, compare activity by gestational age (GA) and sex and derive neonatal screening cut-offs using percentile and WHO methods. DESIGN: Retrospective cross-sectional analysis of cord blood screening programme. SETTING: King Abdulaziz Medical City, Riyadh, Saudi Arabia, January 2016 to May 2022. PARTICIPANTS: All live births with cord blood G6PD and GA. Of 59 465 births, 58 139 (97.8%) were screened. For reference range derivation only, results below the adult threshold (<5.7 U/g haemoglobin (Hb); n=1163) were excluded, yielding 56 976. MAIN OUTCOME MEASURES: Distribution by GA and sex; prevalence under three definitions: adult cut-off (≤5.7 U/g Hb), neonatal percentile cut-off (2.5th percentile) and WHO bands (<30% deficient, 30-70% intermediate, >70% normal). Secondary measures were stratum medians and the male share among detected cases. RESULTS: Mean activity was 15.33±2.67 U/g Hb, higher in preterm than term. Sex differences were absent in preterm strata but present at term (males lower than females; p=0.002). The neonatal 2.5th percentile cut-off was 9.9 U/g Hb. Using the adult cut-off, 2.00% (1163/58 139) were deficient, 80.9% male. Using the neonatal cut-off, prevalence rose to 4.97% (2888/58 139), adding 1725 infants (+583 males, +1142 females) and reducing the male share to 52.8%. WHO bands identified a small <30% group and a female intermediate (30-70%) group across strata. Medians were 15.0 (≥37 weeks), 16.0 (33-36), 17.0 (29-32) and 17.6 (≤28) U/g Hb. CONCLUSIONS: G6PD activity in neonates shows clear GA and sex effects. Adult cut-offs underestimate deficiency, especially in females. Neonatal thresholds (2.5th percentile plus GA-specific WHO bands) improve detection. Adoption within newborn screening, with reporting of a female intermediate band, should strengthen follow-up; external validation and linkage to bilirubin outcomes are needed.