Timing of hyponatremia development in patients with salt-wasting-type 21-hydroxylase deficiency.

Newborn screening (NBS) can detect 21-hydroxylase deficiency (21-OHD), allowing for early treatment initiation. However, many patients present with adrenal crises or hyponatremia at their first visit. Age (in days) of hyponatremia development in infants with salt-wasting (SW)-type 21-OHD remains unclear. Therefore, we determined the earliest age of hyponatremia diagnosis in this retrospective observational study using medical records of 40 patients with classic 21-OHD in Niigata Prefecture, Japan, from April 1989 to March 2019. We determined the earliest diagnosis of hyponatremia (serum sodium levels < 130 mEq/L) and created a sodium decrease rate model to estimate hyponatremia development age. Of 23 patients with SW-type 21-OHD, 10 (43.5%) were identified during NBS; the earliest case to present with hyponatremia was at day 7. Serum sodium levels were significantly and negatively correlated with age in days, and hyponatremia was estimated to develop at 6.6 d after birth. Genotype or serum 17-hydroxyprogesterone levels were not associated with sodium decrease rate. Thus, hyponatremia development age is earlier (within 7 d) than the previously described time-point (10-14 d) in infants with SW-type 21-OHD. Efforts to reduce the time lag from obtaining results to consultation may be required in patients with high 17-hydroxyprogesterone levels on NBS.