Leptin is a globular, slightly acidic protein which can play an important role in the energy metabolism, influences appetite and also displays other functions, not defined precisely yet (e.g. reproduction, haematopoi- esis, metabolism in general, maturation of the organism. This protein has a relatively small molecular weight (14 kD) and is stable at higher temperatures and low pH. Examination of leptin in the blood or liquor has been used mostly in experimental studies of obesity models. No report on leptin examination in urine was found in the literature. With regard to highly favourable physical–chemical properties of leptin, we decided to detect the presence of leptin in probands’ urine. In case of its detection in urine, its possible importance for diagnostics of tubulopathy was studied.
The findings obtained are presented as follows:
1. Examination of the tubular lesion using urinary enzymatic activity (GMT/creatinine index) may be ambigu- ous due to administration of diuretics (all individuals taking saluretics have higher values of this index).
2. Examination of the tubular lesion using urinary enzymatic activity (GMT/creatinine index) is also influenced unfavourably by uroinfection, so that the increase indicates only a higher metabolic activity of cells of the proximal tubule, not tubulopathy.
3. Not all individuals with a tubular lesion have distinct signs of tubular proteinuria on electrophoresis of urinary proteins.
4. Not all individuals with decreased concentrating activity of the kidney and increased fractional excretions of strong ions have leptinuria, but not all these individuals have nephropathy.
5. All probands with tubulopathy have leptinuria (i.e. probands with tubular proteinuria on electrophoresis and also individuals with tubulopathy verified by the GMT/creatinine index and other examinations, including clinical ones.
6. Probands receiving saluretics do not have leptinuria (in contrast to increased GMT/creatinine index).
7. Probands with uroinfection do not have leptinuria (in contrast to increased GMT/creatinine index).
8. Leptinuria correlates with markers of tubulopathy (GMT/creatinine, FEK, albuminuria) and does not correlate with markers of glomerulopathy (selectivity index), but correlates with severity of involved renal functions (concentration of serum creatinine).
On the basis of the above mentioned findings we conclude that all probands of our group under study with diagnosed tubular dysfunction (based on independent examinations and anamnestic data) have leptinuria and its relative excretion increases together with progressing kidney involvement. We found that examination of leptin in urine of our probands is more specific for tubulopathy than examination of urinary enzymatic activity (GMT/creatinine index) and more sensitive than electrophoresis of urinary proteins. This appears to be the first study dealing with leptin analysis in urine for research, diagnostic and therapeutic purposes. Therefore we recommend to use leptin detection in urine for diagnosis of tubular dysfunctions.

        Key words: leptin, urine, kidney, renal dysfunction.