Endocrine Abstracts

Introduction: Primary aldosteronism (PA) is one of the causes of hypertension. Blood aldosterone and the aldosterone/direct renin concentration (DRC) are routinely used as a screening test for PA.

Aim of study: Whether it matters if aldosterone concentration is determined in serum or plasma samples?

Material and methods: 145 healthy males, five females (blood donors) were investigated. In all subjects blood was collected into two tubes: one in EDTA2K (plasma) and one with clot activator (serum). Aldosterone was measured by RIA kit (ZenTch, Belgium), and renin by immunoradiometric kit (CIS bio, France).

Results: In blood donors, the median (and the range) of aldosterone concentration determined in serum was 145 pg/ml (56–369 pg/ml) and in plasma – 289 pg/ml (172–664 pg/ml). These differences ranged 41–75% (median 50%). Correlation between aldosterone in serum and plasma was r=0.9089; r²=0.9385; P<0.01, but plasma aldosterone levels appeared significantly higher in relation to serum aldosterone levels (P<0.0001).

The median and the range of serum aldosterone to plasma DRC indices was 13 (2–45) and of plasma aldosterone to plasma DRC – 26 (5–99). These differences ranged 31–68% (median 50%). Correlation between both indices was r=0.9523; r²=0.9429; P<0.0001, but plasma aldosterone/DRC indices appeared to be significantly higher than serum aldosterone/DRC indices (P<0.0001).

Conclusions: i) Marked differences between the serum and plasma aldosterone levels demand application of separate reference ranges.

ii) Aldosterone/DRC indices may differ significantly depending on whether aldosterone levels are measured in serum or plasma.