Comparison of plasma aldosterone/signal activity and aldosterone/active signal ratios in different clinical conditions
Zoltan Locsei1, Erzsebet Toldy2,5, Dora Horvath1, Rita Nagy1, Karoly Racz3, Istvan Szabolcs6 & Gabor L Kovacs4,5
Because measurement of plasma signal activity (PRA) is time-consuming an automated method directly measuring active signal (REN) may be more suitable for clinical practice. The aim of the study was to analyse the diagnostic utility of REN and aldosterone (ALD)/REN ratio as compared to PRA and ALD/PRA ratio.
Materials and methods: PRA, REN (DiaSorin) and ALD (Immunotech) were simultaneously measured in 123 plasma samples (83 females and 40 males; mean age, 42±16 years) including samples from 38 healthy volunteers with normal blood pressure and without medication (controls), 25 healthy females taking oral contraceptives and 60 patients with verified hypertension (22 treated and 38 untreated). In the latter group 15 patients have adrenal adenomas.
Results: In the whole group of samples there was a weak but significant correlation (r=0.59; P<0.001) between PRA (1.24±1.26 ng/ml per h) and REN (28.7±44.4 μU/ml). In the lower concentration (PRA: 0.45±0.25 ng/ml per h; REN: 9.4±10.1 μU/ml) the correlation was weaker (r=0.38; P<0.001). PRA was undetectable in 11%, while REN in 4% of the samples. The ALD/REN ratio, but not the ALD/PRA ratio, was significantly (P<0.05) higher in women taking oral contraceptives than in those who did not (ALD/REN ratio, (40.6±37.9 vs 22.5±21.9 pmol/l per μU per ml). In hypertensive patients treated with β blockers the ALD/REN ratio was significantly higher (P<0.001, 119±111 pmol/l per μU per ml) than in controls, and in hypertensive patients taking medications other that β blockers (23±16 and 25±26 pmol/l per μU per ml, respectively). In patients with adrenal adenoma the ALD/PRA ratio, but not the ALD/REN ratio, was significantly higher than in controls (ALD/PRA ratio 41±104 vs 11±23 ng/dl per ng per ml per h).
Conclusions: There is a poor analytical correlation between the two methods, especially in the lower range of PRA/REN concentrations. The widely used screening method (ALD/PRA) should be replaced by the ALD/REN ratio only after careful interpretation of the different clinical conditions.