Comparative study of sodium, potassium, ionized calcium, urea and creatinine circadian rhythm documented in samples of capillary and venous blood from healthy subjects.

Circadian rhythms of sodium, potassium, ionized calcium, creatinine and urea concentrations were determined in venous and capillary blood of practically healthy volunteers (10 women and 8 men). Electrolytes were determined on the ionoselective analyzer Microlyte (KONE, Finland). Circadian rhythmicity of parameters was revealed in venous and capillary blood by means of group-mean cosinor analysis. Acrophases of the rhythms occurred in the late evening (Na) or in the first (K, venous ionized Ca) and in the second half (creatinine, urea) of sleep. Circadian rhythms of electrolytes (except ionized Ca rhythm) and final products of nitrous metabolism in capillary blood turned out to be the markers of the corresponding indices rhythms of venous blood.