Establishing Reference Ranges for Aldosterone, Renin and Aldosterone-to-Renin Ratio for Women in the Third-Trimester of Pregnancy.

Objective: Diagnosis of primary hyperaldosteronism in pregnancy is complicated due to lack of reference ranges for aldosterone, renin and aldosterone-to-renin ratio. We have endeavoured to establish third-trimester reference ranges for the above-mentioned parameters.

Design & patients: We performed postural tests for aldosterone and renin (chemiluminescence immunoassay Liason® DiaSorin Inc., Italy) in 70 healthy pregnant women (age 30.53±4.51 years), at 32.38±4.25 weeks of gestation and in 22 non-pregnant healthy women (age 33.08±8.72 years).

Results: Aldosterone reference ranges were 6.51-73.97 ng/dl and 12.33-86.38 ng/dl, for supine and upright positions, respectively and that for renin were 6.25-59.36 µIU/ml and 11.12-82.55 µIU/ml, respectively. Aldosterone and renin concentrations were higher in an upright position (p=0.000459 and p=0.00011, respectively). In contrast, aldosterone-to-renin ratio was not affected by posture (i. e. 0.497-3.084 ng/dl/µIU/ml versus 0.457-3.06 ng/dl/µIU/ml, p=0.12), but was higher (p=0.00081) than in non-pregnant controls. In comparison to manufacturer-provided non-pregnant reference range, supine aldosterone concentrations increased by 556% (lower cut-off) and 313% (upper cut-off), while upright aldosterone concentrations increased by 558% (lower cut-off) and 244% (upper cut-off). The reference range for supine renin concentrations increased by 223% (lower cut-off) and 48.7% (upper cut-off), while upright renin concentrations increased by 253% (lower cut-off) and 79% (upper cut-off).

Conclusions: There is an upward shift in aldosterone and renin reference ranges in the third-trimester of pregnancy accompanied by an increase in an aldosterone-to-renin ratio, that is not influenced by posture. It remains to be established whether the aldosterone-to-renin ratio may be used as a screening tool for primary hyperaldosteronism in pregnancy.