Identification of cystatin C as a new marker of glomerular filtration rate, and of shrunken pore syndrome - a new kidney disorder defining selective glomerular hypofiltration syndromes - calls for expansion of the international KDIGO guidelines.

Cystatin C was identified as a marker of glomerular filtration rate (GFR) in 1979, and the parallel analysis of cystatin C and creatinine led to the identification of shrunken pore syndrome (SPS) - a new kidney disorder - in 2015. Since then, it has been shown that cystatin C in many aspects is superior to creatinine as a marker of GFR and cardiovascular risk. SPS, an entity within the selective glomerular hypofiltration syndromes (SGHS), has been demonstrated to be associated with a strong increase in morbidity and mortality in several populations. Despite the seriousness of SPS and SGHS, and the availability of potential treatments, many patients with these conditions remain undiagnosed, due to the limitations of the international Kidney Disease Improving Global Outcomes Organization (KDIGO) guidelines. Given the significant clinical advantages of cystatin C in diagnosing and treating kidney disorders, there is a need to expand the KDIGO guidelines to include cystatin C measurements alongside creatinine at least in the initial patient evaluation but also in follow-up evaluations. This would improve the early detection and management of patients with kidney diseases, ultimately enhancing patient outcomes. The present discourse summarizes the development of this understanding from the original observations in 1979 and 2015 to the latest findings.