Biomarkers of renal function, which and when?

PURPOSE OF THE REVIEW: Acute kidney injury (AKI) and chronic kidney disease (CKD) are conditions that substantially increase morbidity and mortality. Although novel biomarkers are being used in practice, the diagnosis of AKI and CKD is still made with surrogate markers of GFR, such as serum creatinine (SCr), urine output and creatinine based estimating equations. SCr is limited as a marker of kidney dysfunction in both settings and may be inaccurate in several situations, such as in patients with low muscle mass or with fluid overload. New biomarkers have the potential to identify earlier patients with AKI and CKD and in the future potentially intervene to modify outcomes.

RECENT FINDINGS: In particular KIM-1 and NGAL are considered excellent biomarkers in urine and plasma for the early prediction of AKI; however cycle arrest biomarkers have emerged as novel markers for risk stratification of AKI. Urine TIMP-2 and IGFBP7 performed better than any other biomarkers reported to date for predicting the development of moderate or severe AKI. Biomarker combinations are required to increase diagnostic accuracy in an acute setting. NGAL, cystatin C, and FGF-23 are promising and accurate biomarkers for CKD detection. Equations combining cystatin C and SCr perform better than the equations using either cystatin C or SCr alone, especially in situations where CKD needs to be confirmed. Combining creatinine, cystatin C and urine albumin to creatinine ratio improves risk stratification for kidney disease progression and mortality.

SUMMARY: Recent advances in molecular biology have resulted in promising biomarkers for AKI and CKD diagnoses; however more research is necessary to implement them successfully into clinical practice in order to facilitate early diagnosis, guide interventions and monitor disease progression. The following review describes the most important biomarkers studied in kidney disease and will discuss the use and the value of these biomarkers in different clinical settings.