Performance evaluation of a direct chemiluminescence assay for 25-hydroxyvitamin D and its application in assessing vitamin D status among reproductive-age women in southeastern China.

backgroundVitamin D deficiency is a global public health concern, and women of reproductive age represent a particularly vulnerable population. Accurate measurement of serum 25-hydroxyvitamin D [25(OH)D] is therefore essential for reliable clinical assessment. This study aimed to evaluate the analytical performance of the Innodx vitamin D assay for 25(OH)D measurement and to investigate the prevalence of vitamin D deficiency among women of reproductive age in southeastern China.

methodsThis cross-sectional study enrolled women of reproductive age (20-45 years) who sought medical services at Xiamen Maternal and Child Health Hospital in China between November 2023 and September 2025. Serum 25(OH)D levels were measured to determine vitamin D status using the Innodx vitamin D assay (Xiamen Innodx Biotech Co., Ltd., Xiamen, China). The analytical performance of the assay was validated according to Clinical and Laboratory Standards Institute (CLSI) guidelines, covering precision, accuracy, linearity, and interference. A method comparison was performed against liquid chromatography-tandem mass spectrometry (LC-MS/MS) and the Roche electrochemiluminescence assay. Based on the measured levels, vitamin D status was categorized as deficient (< 20 ng/mL), insufficient (≥20, < 30 ng/mL), or sufficient (≥ 30 ng/mL).

resultsThe intra-assay coefficients of variation (CV) were 3.18%, 2.09%, and 1.86% at three concentration levels (5, 25, and 100 ng/mL), while intermediate precision CVs were 4.34%, 3.64%, and 3.17%, respectively. Accuracy testing showed bias of 4.20% and 3.26% at 20 and 50 ng/mL. The assay demonstrated excellent linearity (R2 = 0.998) across the range of 4.0-150.0 ng/mL. No significant interference was observed from hemoglobin (100 mg/dL), bilirubin (40 mg/dL), triglycerides (400 mg/dL), or rheumatoid factor (600 IU/mL). In method comparison with LC-MS/MS, the Innodx vitamin D assay demonstrated strong concordance with a Pearson correlation coefficient of r = 0.970. When compared with the Roche vitamin D assay, the Innodx showed better correlation with LC-MS/MS. Among 495 women, the mean 25(OH)D concentration was 20.50 ± 7.88 ng/mL, with 88.9% (95% CI: 86.1%, 91.7%) having vitamin D deficiency or insufficiency. Women aged ≤ 25 years showed significantly lower levels (18.38 ± 6.26 ng/mL) compared to older groups (31-35 years: 23.31 ± 8.97 ng/mL; > 35 years: 23.72 ± 8.56 ng/mL) (P < 0.05).

conclusionThe Innodx vitamin D chemiluminescence assay demonstrated satisfactory analytical performance for clinical use. Our findings reveal a high prevalence of vitamin D deficiency among reproductive-age women in southeastern China, particularly in younger age groups, highlighting the need for public health interventions.