Cases of Congenital Adrenal Hyperplasia Missed by Newborn Screening in Minnesota FREE

To the Editor: The purpose of newborn screening (NBS) for congenital adrenal hyperplasia (CAH) due to 21α-hydroxylase deficiency is the early identification of newborns with the classic salt-wasting (SW) and simple-virilizing (SV) forms to avoid a potentially life-threatening adrenal or salt-wasting crisis. Cases of classic CAH missed by NBS (false-negatives) are not well documented.¹

Population-based study of all newborns screened in Minnesota (N = 838 241) from January 1999 through December 2010 was performed. As in most NBS programs in the United States, samples were collected 24 to 48 hours after birth and 17α-hydroxyprogesterone level was measured by a time-resolved fluoroimmunoassay (Table 1). Through a partnership between the Minnesota Department of Health and the 3 largest pediatric endocrinology centers in Minnesota, cases of CAH missed by NBS were identified through review of the NBS registry and the medical records of the participating institutions. Institutional review boards at all sites approved the study with waivers of informed consent.

Confirmation of classic CAH of those identified and missed by NBS was based on elevated serum 17α-hydroxyprogesterone levels, clinical and biochemical presentation, and in some cases, molecular testing of the CYP21A2 gene using a common mutation panel or sequencing.² Computations were performed using the Binom package in R (R Foundation for Statistical Computing).

Of the 838 241 newborns screened during the period, 52 patients with classic CAH were identified and 15 cases were missed (false-negative rate, 22.4%; 95% CI, 14%-34%); 6 males, 9 females; 10 SV, 5 SW) (Table 2).

Among the 9 females missed by NBS, 3 had ambiguous genitalia at birth (cases 9, 10, and 15) but were not identified until 3.4 years, 6.5 years, and 3 months of age, respectively. Case 10 had vaginoplasty 6 years before diagnosis. Ambiguous genitalia identified cases 1, 2, 3, 4, and 14. Case 3 was originally assigned the male sex and diagnosed a few days later after workup for penoscrotal hypospadias.

The CAH males missed by NBS (cases 6, 7, 8, 11, and 13) were not diagnosed until ages 2.3 to 5.5 years (except case 5) and had significant bone age advancement (median of 7 years difference between bone age and chronological age). Case 6 presented at age 4 years and was thought to have a left adrenal tumor. He underwent adrenalectomy with histopathology suggestive of CAH.

Over a 12-year period, 22% of diagnosed patients born in Minnesota with classic CAH were not identified by NBS, highlighting that a negative screening result does not definitively rule out classic CAH. We also found that a false-negative result can sometimes delay the diagnosis of CAH even in a newborn female with ambiguous genitalia.

A study limitation is the probability that false-negatives are underestimated due to patients with CAH not yet diagnosed, patients who moved out of the state, or infants who passed away with unidentified CAH.

While other studies have reported some missed cases of SV-CAH,³ our study is one of the first to document the extent to which both cases of SV-CAH and SW-CAH are missed by NBS. Sensitivity of NBS for SW-CAH is generally reported as 100%,¹ with only 1 report from Germany identifying 2 cases of SW-CAH missed over 7 years at 24 institutions.⁴ The lack of a consistent follow-up reporting system for physicians to alert their state's health department when a patient is diagnosed with classic CAH later in infancy or childhood may explain why more missed cases of classic CAH have not been reported.

Similarities in NBS procedures in most US states suggest that false-negative results may be underestimated nationwide. However, the reason for false-negative results is unclear. An unexplained delayed increase in 17α-hydroxyprogesterone level in certain patients with classic CAH and/or the timing and sensitivity of the assay are possibilities. The false-negative results were not due to procedural changes because 1 to 2 false-negative results were found every year from 1999 through 2010 except 2002, which had none.

Screening programs should educate clinicians about false-negative results so that any patient for whom there is clinical concern for CAH can receive immediate diagnostic testing, particularly females with ambiguous genitalia.