Normal and abnormal day-to-day variability of urinary albumin excretion incontrol and diabetic subjects

Urinary albumin excretion (UAE) is very variable from day to day. This vari ability, more or less potent, might by itself have a patho-physiological si gnificance. We analyzed day-to-day UAE in 207 elderly (60-75 years) inpatie nts (134 with and 73 without diabetes mellitus) attending the department of internal medicine of the Angers University hospital. Twenty-four-hour urin e was collected 3 times during a 5-10 day hospitalization period. One-hundr ed-fifty-one patients (73%) displayed normoalbuminuria (UAE < 30 mg/24 h in 2 or 3 measures) while 56 patients (27%) had microalbuminuria (UAE within 30-300 mg/24 h in 2 or 3 measures). As the raw data of UAE was not normally distributed, we transformed UAE into the variable z = log (log (k + UAE)) where k is an integer and looked for a k value for which z might be normall y distributed. We found that z was actually normally distributed for k = 2. Mean value and coefficient of variation of z in the 3 measurements were us ed to define the level and the temporal intra-individual variability of UAE . Expressed in term of z, the day-to-day intra-individual variability of UA E showed a potent change (from large variability to small variability) at t he particular level z = 1.25, corresponding to UAE = 30.8 mg/24 h. This val ue is precisely the level currently used to define microalbuminuria in diab etic subjects. It is remarkable that the day-to-day variability of UAE coll apses when UAE crosses the level which has been used to define microalbumin uria.