IMPE Abstracts

Introduction: The National Program for Strengthening Neonatal Screening (Ministry of Health, Argentina) provides diagnostic reagents to 20 provincial NS centers in Argentina. CAH NS requires the use of appropriate cut-off values in order to detect all true positive cases, minimizing the recall of false positive cases, to reduce the negative impact on families due to unnecessary alerts and the need of confirmatory tests. The NS Laboratory of Hospital of Pediatrics JP Garrahan, Buenos Aires, Argentina receives samples from 50 maternity wards from 4 provinces of southern Argentina (Tierra del Fuego, Santa Cruz, Chubut, Río Negro).

Objectives: To obtain updated gestational age-adjusted cut-off values for the methodology in use for CAH NS (ELISA).

Materials and methods: A commercial enzyme immunoassay kit, Elizen Neonatal 17-OHP Screening, provided by the Ministry of Health was implemented in a NS program (February to September 2022), measuring 17OHP in 21495 unselected samples, 36 hs to 5 days of life. Preliminar gestational age-adjusted cutoff values were initially calculated as the 99^th percentile of a population of 3296 unselected samples (Cutoff 17OHP (ng/ml serum) G≤34: 162.2 n=58; G35: 99.2 n=78; G36:77.2 n=146; G37:69.3 n=330; G≥38:55.8 n=3296). Using these preliminary cut-off values, 21492 newborns were screened. p95, p99.5 and p99 percentiles, mean, SD were calculated.

Results: 3 cases of CAH were detected and confirmed in the evaluated samples. CAH incidence: 1:7165. The 3 confirmed samples were excluded from the statistical calculation.

Distribution of 17-OHP (ng/mL serum):

Sensitivity 100% Specificity 98.76 % False Positive Rate: 1.24% Positive Predictive Power 1.12%

Conclusions: Based on our results. New gestational age-adjusted cut-off values were defined for the Elizen Neonatal 17-OHP Screening kit (Zentech). Using p99 for GA>36 weeks and more conservative percentiles (p95 and p97.5) in the groups with lower n and lower gestational age (GA<37).