The Investigation of the Effect of Electrolyte Disorder on Sweat Test in Newborns with Positive Cystic Fibrosis Screening

Background and objectives: The aim of this study is to investigate the effect of the electrolyte and acid-base status present at the time of admission to the hospital on the sweat test (ST) of the patients who were found to have a positive newborn screening test (NST) for Cystic Fibrosis (CF). Methods: The patients who referred to pediatric pulmonology clinic for ST with positive NST for CF and diagnosed as CF were analyzed retrospectively. From the medical records acid-base status measured simultaneously with the ST and with serum sodium, potassium, and chloride levels were included in the study. Results: The study completed with 37 patients who met the inclusion criteria. At the time of ST, the mean sodium, potassium and chlorine values were 134.83±4.25 (122.0-141.0), 4.94±0.95 (2.9-7.6) and 97.72±12.40 (64.0-116.0) mEq/L, respectively. Patients whose electrolytes were measured at the time of diagnosis, 27.0% (n=10) had hyponatremia, 8.1% (n=3) had hypokalemia, and 4.8% (n=1) had hypochloremia. There was a significant difference between serum chloride and bicarbonate levels according to the negative, borderline, positive ST groups (p=0,036). In addition, no significance detected between the sweat test values of patients with Pseudo-Bartter Syndrome (PBS) (38.7%) and without. Conclusion: The chloride level during ST is lower in patients with borderline and negative ST results. The mean potassium and chloride values of the patients with PBS are lower while the mean bicarbonate value is higher. This may cause false negative results in ST. So, it is important to check the serum electrolyte levels before the ST is performed in the newborn screening positive baby.