*3.2. Serum or Plasma Markers*

Reasonable data only concern cystatin C and NGAL. The results of the studies presented provided enough information to consider cystatin C as a better marker of eGFR than creatinine after exercise and at rest in athletes with high or low lean mass [28–30]. The information concerning plasma or serum NGAL is more questionable. In fact, after some exercises, NGAL is elevated. However, NGAL is also a marker of inflammation, organ damage and hypoxia, and in exercise, it seems to have low specificity for AKI. One practical problem is the huge variability of levels between studies and subjects. One of the possible implications of p/sNGAL measurement is diagnosis of subclinical AKI in uncomplicated rhabdomyolysis, when creatinine and cystatin levels are within the normal range [62].

The general problem with serum measurement after exercise is hemoconcentration. In many publications, the authors used a correction of the effect of dehydration according to Dill and Costill's method [63], on the basis of changes in pre- and post-blood morphology. This approach is reasonable in experimental studies, but in clinical practice, it is difficult to use, because pre-injury blood morphology results are unknown.

Suggestion: We suggest measuring sCyst-C instead of creatinine in future studies of kidney function in exercise. It is reasonable to check sNGAL in the risk group with rhabdomyolysis.
