Efficacy of Liquid-chromatography and Radioimmunoassay in False-positives' Drop-off in CAH Newborn Screening.

CONTEXT: The main challenge in congenital adrenal hyperplasia newborn screening (NBS) is the high rate of false-positive results, emphasizing the need for specific serum confirmatory tests. Data on the effectiveness of serum 17-hydroxyprogesterone (17OHP) measurements using available methodologies remain limited.

OBJECTIVES

To evaluate the efficacy of confirmatory tests using measurements of serum steroids by radioimmunoassay (RIA) and liquid chromatography tandem mass spectrometry (LC-MS/MS) methodologies.

DESIGN AND

SETTING

A prospective longitudinal cohort study.

PATIENTS: Data of 708 437 newborns (NBs) were evaluated.

METHODS

Neonatal-17OHP (N17OHP) results ≥ 2 × 99.5th were recalled for serum dosages by RIA (17OHP), by LC-MS/MS (17OHP, 21-deoxycortisol-21DF, androstenedione-Δ4, and cortisol) and positive predictive values (PPV) were determined. Altered hormonal results were submitted to CYP21A2 genotyping. Nonparametric tests and receiver operating characteristic (ROC)-curves were used.

RESULTS

Recall rate of N17OHP (first tier) was 0.03% and serum 17OHP levels remained increased in 26% (RIA) and 11% (LC-MS/MS) of NBs, yielding PPV of 30% and 49%, respectively. Fifty-eight NBs were diagnosed with classical forms, and 32 asymptomatic NBs persisted with increased serum 17OHP levels. ROC-curves between false and true-positive tests disclosed highest diagnostic performance for 17OHP/LC-MS/MS [cutoff 48.3 ng/mL (146.3 nmol/L) = 100%-sensitivity]. The (17OHP+Δ4)/cortisol ratio presented the highest discriminative ability (cutoff 24.9 = 100%-PPV); serum 21DF presented a good performance and was comparable to 17OHP measured by LC-MS/MS (99%-specificity).

CONCLUSION

Measurement of 17OHP by LC-MS/MS provides the best performance for serum confirmatory tests and may be complemented by the (17OHP+Δ4)/cortisol ratio analysis. Genotyping is useful mainly to resolve persistently indeterminate biochemical results.