Neonatal cystic fibrosis screening: Analysis and differences in immunoreactive trypsin levels in newborns with a positive screen

Abstract

Introduction: Neonatal cystic fibrosis (CF) screening has enabled the disease to be diagnosed early, and is a determining factor in the increase in survival of these patients. Its main disadvantage is its low specificity and elevated number of false positives. The aim of this study is to analyse the differences in immunoreactive trypsin (IRT) between the different groups of newborns (NB) with a positive neonatal screen depending on whether they were healthy, healthy carriers, affected by CF, or CFSPID (Cystic Fibrosis Screen Positive, Inconclusive Diagnosis). Material: Retrospective analytical study of the concentrations of IRT in NB with a positive neonatal screen for CF born in a tertiary hospital during an 8-year period. Results: A total of 790 NB with a positive neonatal screen for CF were analysed. Of these 86.3% were term, 53% girls, and 11.8% were admitted. The mean IRT value was 79.16 ng/mL (range 60–367). Significantly higher concentrations of IRT were found in those affected by CF compared to the other groups (P < .001). There were higher levels in large prematures (P = .007) and admitted patients (P = .002). There were no differences as regards gender or season. There was a direct correlation of 64% (P = .001) between IRT and sweat test in those affected by CF and CFSPID. A cut-off value of IRT for the diagnosis of CF was calculated from the ROC curve (76.2 ng/mL (S = 95.7%, Sp = 64.5%). Conclusions: NB with CF have significantly higher levels of IRT than healthy ones, or carriers and CFSPID. Prematurity and hospital admission may also have an influence. A higher IRT value is associated with a higher level in the sweat test. Resumen: Introducción: El cribado neonatal de fibrosis quística (FQ) ha permitido el diagnóstico precoz de la enfermedad, siendo determinante en el aumento de supervivencia de estos pacientes. Su principal inconveniente es su baja especificidad y elevado número de falsos positivos. El objetivo fue analizar las diferencias de tripsina inmunorreactiva (TIR) entre los diferentes grupos de recién nacidos (RN) con cribado neonatal positivo según fueran sanos, portadores sanos, afectos de FQ o Cystic Fibrosis Screen Positive, Inconclusive Diagnosis (CFSPID). Material: Estudio retrospectivo analítico de las concentraciones de TIR en RN con cribado neonatal positivo para FQ nacidos en un hospital de tercer nivel durante 8 años. Resultados: Se analizaron 790 RN con cribado neonatal positivo para FQ, 86,3% a término, 53% niñas y 11,8% ingresados. El valor medio de TIR fue 79,16 ng/mL (rango 60–367). Se encontraron concentraciones significativamente más elevadas de TIR en afectos de FQ con respecto a los otros grupos (p < 0,001). Existen niveles superiores en grandes prematuros (p = 0,007) e ingresados (p = 0,002). No difieren en cuanto a sexo o estacionalidad. Existe una correlación directa del 64% (p = 0,001) entre TIR y test del sudor en afectos de FQ y CFSPID. Mediante curva ROC se calculó el valor de corte de TIR para el diagnóstico de FQ, que fue 76,2 ng/mL (S = 95,7%, E = 64,5%). Conclusiones: Los RN con FQ presentan cifras significativamente más elevadas de TIR que sanos, portadores o CFSPID. La prematuridad y hospitalización también pueden influir. Un mayor valor de TIR se relaciona con una mayor cifra en el test del sudor.

Keywords

• Tripsina inmunorreactiva
• Cribado neonatal
• Fibrosis quística