Short-term and long-term intra-individual variations and critical differences of clinical chemical laboratory parameters.

Twenty eight clinical chemical blood parameters were studied with respect to intra-individual variations. Both short term variations, within one day and during one week, and long term variations, during a six months period, were investigated in groups of 62, 16 and 274 individuals. Moreover, critical differences were calculated from the total variations, i.e. physiological (personal) and analytical variations. The influences of external factors (sex, smoking, and oral contraceptives) were being studied. It was concluded that the use of laboratory data in clinical diagnosis is considerably improved when intra-individual variations and critical differences are used.