The utility of renin measurement in guiding mineralocorticoid replacement is unclear. To address this we retrospectively examined the parameters and treatment of 97 patients with Addisons disease over a five year period.
Methods: Adrenal replacement, blood pressure (BP), orthostatic BP response, urea, sodium, potassium and renin levels of 97 patients attending our clinic were collected over the period 20122016. Data were analysed in R version 3.3.2.
Results: 97 patients attending for 397 appointments were reviewed. Renin level was measured on 227 (57%) of attendances, 68% were elevated (>45mU/L) with 48% above 90 mu/L. A modest but significant negative association with plasma sodium (P<0.001, R2 0.189) and a significant but weak association with potassium (P<0.001. R2 0.062) and urea (P<0.001, R2 0.053) were noted. There was no association with systolic or diastolic BP or orthostatic response. A renin level >90 mu/L was 64% sensitive and 28% specific for detecting another feature of mineralocorticoid deficiency (hyponatraemia, hyperkalaemia, postural drop). A renin level >45 ml/l was 79% specific but only 24% sensitive. Measurement of renin was more likely to stimulate an adjustment in fludrocortisone dose (chi2 P=0.019) however, patients with a deranged renin level were as likely to have a dose change as those with a normal renin level (545 mU/L, chi2 P=0.454). Of the 77 patients with renin levels greater than twice the upper limit of normal, a dose increase occurred in only 23 patients (29%), in 17 of whom, sodium, potassium and postural BP were unremarkable.
Conclusion.: Our study suggests that although renin level does have important clinical correlates with serum biochemistry, high renin levels have only modest sensitivity and low specificity for detecting other features of mineralocorticoid deficiency. This is reflected in a high variability in therapeutic response to deranged renin levels and the role of renin in guiding management of patients with Addisons disease remains undefined.