Aldosterone Measurement	

The normal production rate is approximately 200µg daily; this is critically dependent on sodium intake being stimulated by sodium depletion and suppressed by salt loading. Plasma levels fall in the range of 140–420pmol/l (50–150ng/l) when normal subjects are recumbent and of 420–840pmol/l (150–300ng/l) when standing upright. In addition, there is a circadian rhythm of aldosterone secretion. Thus, posture, sodium intake, and time of day all have to be taken into consideration when taking blood samples for aldosterone assay. 

See also: 
• Circadian Variation of Aldosterone Secretion