Oliguria, creatinine and other biomarkers of acute kidney injury.

Acute kidney injury (AKI) and fluid overload are conditions that require an early diagnosis and a prompt intervention. The recognition of these pathologic conditions is possible in the early stages if specific signs and symptoms are taken into account. Among them, oliguria represents an important sign. Reduced urine output for a certain number of hours may be an important sign of kidney dysfunction. This must be evaluated in conjunction with other factors such as hydration status and use of drugs. At the same time, traditional markers of kidney function such as urea nitrogen and creatinine must be evaluated in light of a possible altered balance. Increased levels may be due to reduced kidney function but also increased generation or altered solute distribution space due to non-optimal hydration status. Finally, novel biomarkers for renal tissue damage are becoming popular. Molecules such as NGAL or cystatin C may become altered well before creatinine or oliguria signal a condition of reduced kidney function. Here, the difference between insult and dysfunction becomes evident. Novel biomarkers seem to enable the clinician to make early diagnosis of kidney damage, distinguishing between AKI and acute kidney failure. Reduced glomerular filtration rate is, in fact, a late event in the continuum of the AKI syndrome.