Performance of Plasma Renin Assays in Guiding Mineralocorticoid Dosing in Children With Adrenal Insufficiency

Plasma renin is measured in children with salt-wasting adrenal insufficiency (AI) as part of assessing the adequacy of mineralocorticoid (MC) replacement. It is recommended that plasma renin is used to monitor MC replacement. This can be measured as either plasma renin concentration (PRC) or activity (PRA); it is not known if one method is preferable over the other.

Samples from 129 patients less than 18-years old requested for PRC were selected randomly. PRC was measured using the IDS-iSYS chemiluminescence immunoassay, PRA was measured by LC-MS/MS. The PRC and PRA values for each sample were reviewed using published reference ranges and categorised as low, normal and high. Samples which showed disagreement between PRC and PRA results based on the reference ranges were divided into groups. Samples collected from patients attending the regional adrenal clinic were clinically reviewed in retrospect, using serum sodium and blood pressure as decision guides, to determine if MC replacement dosing would differ if PRA was used instead of PRC.

Ninety-six (74%) of the samples analysed exhibited agreement between their PRC and PRA interpretation. Seventeen of 33 samples which displayed disagreement were collected from adrenal clinic patients. Of these, eight would have a different clinical decision concerning MC replacement based on PRA compared with PRC. In each of these instances, adjustments to MC dose based on PRA was strongly supported by serum sodium levels and blood pressure centiles. In one instance, PRC had been deliberately ignored by clinicians and MC dose had been adjusted according to other conventional parameters such as blood pressure and serum sodium. In this instance, PRA provided reassurance that MC replacement had been correctly assessed by clinicians.

Our investigation found PRA performed superiorly to PRC for assessing MC replacement in paediatric patients, based on supporting biochemical and clinical parameters. Our results indicated that use of PRA may help to standardise practice when assessing MC replacement; this is likely to have patient benefit through improved blood-pressure and electrolyte control.