URINARY ELEMENT CONCENTRATIONS IN KIDNEY-STONE FORMERS AND NORMAL CONTROLS - THE WEEKEND EFFECT

Early morning urines were collected on each of three days (Monday-Wedn esday) from 19 male stone-formers and 20 healthy male controls. Concen trations of 10 elements were determined using inductively coupled plas ma atomic emission spectroscopy, graphite furnace atomic absorption sp ectroscopy and particle induced x-ray emission spectrometry. Data were treated using multivariate statistical methods. The results showed th at the concentrations of several elements in the control urines were s ignificantly raised on Mondays and that controls and stone formers dif fered with respect to certain elements, also on Mondays. The observed elevations were termed the ''weekend effect''. It is suggested that wh ile stone-formers may regulate their diets throughout the entire week, normals may indulge in dietary excesses over the weekend. The weekend effect highlights the danger of placing too much emphasis on a single measurement of a urinary parameter and alerts investigators to take c ognizance of the day on which urine collections are effected, especial ly when attempting to identify abnormal renal excretion patterns in st one-formers by comparison of their urinary variables with those of con trols.