Trimester-specific reference intervals for serum N-acetyl-β-D-glucosaminidase in healthy pregnant women in Hainan, China

The absence of gestational age-specific reference intervals for serum N-acetyl-β-D-glucosaminidase (NAG) in pregnant women may lead to clinical misinterpretation. This study aimed to establish trimester-specific reference intervals for serum NAG in healthy pregnant women from Hainan, China, and to characterize its dynamic changes throughout gestation. In this cross-sectional study, 2416 healthy women with singleton pregnancies were stratified by gestational age into three groups: first trimester (1–12 +6 weeks; n = 1295), second trimester (13–27 +6 weeks; n = 670), and third trimester (28–40 weeks; n = 451). Serum NAG levels were measured, and trimester-specific reference intervals were established using the 2.5th to 97.5th percentiles. Serum NAG concentrations increased significantly with advancing gestation (P < 0.0001). The established reference intervals were 12.0–40.0 U/L for the first trimester, 16.0–63.2 U/L for the second trimester, and 29.3–107.0 U/L for the third trimester—all substantially higher than those of the non-pregnant control group (8.0–23.4 U/L). The median NAG level in the third trimester (56.2 U/L) represented a 143 % increase compared to the first trimester (22.5 U/L). This study provides the first gestational age-specific reference intervals for serum NAG in pregnant women in a tropical region of China. The findings confirm that physiological NAG levels increase progressively with gestational age. The use of non-pregnant reference intervals in clinical practice may lead to misclassification of renal function during pregnancy, underscoring the necessity of adopting trimester-specific reference standards in prenatal laboratory settings.