*3.3. Urinary Markers*

The urinary markers are increased after almost every exercise. The increment is rather small but consistent with individuals. The changes are dependent on the duration and intensity of exercise. Most studies investigated changes in uKIM-1 and uNGAL. After short exercise, an increase in uKIM-1, but not uNGAL, was observed. Elevated uKIM-1 was observed 2 and even 9 days after prolonged exercise. It is difficult to discuss the utility of uL-FABP, uCyst-C and other markers, because only few studies were performed. L-FABP is a marker of hypoxia, therefore it could be an ideal marker for studies in exercise but was used only in very few studies from one study group. What is also surprising is that uIGFBP-7 and uTIMP-2 were only analyzed in one study, and were the only markers approved for early diagnosis of AKI. The methodological problem with interpreting the changes in urinary markers is normalization. It is known that all urinary markers can be diluted, and, e.g., normalization of albuminuria is a standard procedure. In some studies, un-normalized values are used, but most authors normalized AKI markers to creatinine, osmolality, urine flow or cystatin C [18,23,26,27,34,35,40,44–48,51,53]. All these approaches had some limits. The most common was normalization to creatinine.

Suggestion: There is a need for studies on follow-up. Studies showing changes in urine markers shortly after exercise are interesting but have little practical value. In clinical practice, AKI is suspected and diagnosed several hours after exercise. What is most important is what levels of markers are typical for AKI 3, 6, 12 or 24 h after exercise. Although normalization to creatinine has some limits, it is the most common approach, and therefore it is reasonable to use this kind of normalization in subsequent studies.

There is no biomarker specific enough to assess AKI as a single biomarker. There is also no panel assessment using a couple of biomarkers, except combined urinary IGFBP-7 and TIMP-2. Taking into account the results presented in this review, combined uKIM-1/uCr and uNGAL/uCr could be the best to exclude or diagnose AKI after exercise.
