Intrasubject reproducibility of supine norepinephrine plasma concentrations in patients with cardiovascular sympathetic failure.

Background: Plasma levels of the catecholamine norepinephrine (NE) has emerged as a useful tool to help differentiate pre- and post-ganglionic disorders in patients with cardiovascular autonomic failure (AF). However, data on intrasubject reliability in individuals with these conditions are limited. We evaluated the intrasubject reproducibility of supine plasma NE levels drawn across two consecutive time points under controlled conditions during head-up table testing in a large cohort of patients with alpha-synucleinopathies and both pre- and post-ganglionic cardiovascular AF.

Methods: Antecubital venous blood drawn via an indwelling cannula with the subject supine was assayed for plasma level of catecholamines. We collected two consecutive samples, the first after 20 min of supine rest (NE1) and the second 5 min later (NE2), from a group of 279 participants including 57 with Parkinson's disease/Lewy body dementia (44 M; 65.5 ± 11.1 y), 131 with multiple system atrophy (81 M; 63.2 ± 8.5 y), 41 with pure autonomic failure (25 M, 65.1 ± 9.3 y), and 50 healthy controls (27 M; 46.7 ± 19.4 y).

Results: We found no difference between NE1 and NE2 (p = 0.645), with a mean intrasubject reproducibility (NE maximum - NE minimum) × 100 / NE maximum) of 11.5 % ± 10.64. This finding was confirmed when controlling for diagnosis (p = 0.669), gender (p = 0.493), age (p = 0.865), disease duration (p = 0.596) or considering all factors together (p = 0.527).

Conclusions: We found excellent test-retest reliability of consecutive supine NE measurements in patients with alpha-synucleinopathies and cardiovascular AF, independent of age, gender and disease duration. This lends evidence to support the use of a single supine NE measurement in these conditions.