Shrunken pore syndrome and mortality: a cohort study of patients with measured GFR and known comorbidities

Shrunken pore syndrome (SPS) is defined by a cystatin C-based estimation of glomerular filtration rate (eGFR(CYS)) being less than 60% or 70% of a creatinine-based GFR estimation (eGFR(CR)) in the absence of extrarenal influences on cystatin C or creatinine concentrations. SPS has been associated with a substantial increase in mortality or morbidity in all investigated populations. However, in these studies, neither the diagnoses, nor causes of death were described, and only estimated GFR was available. The present study concerns 2781 individuals with measured GFR (mGFR), known diagnoses, and known causes of death during 5.6 years in median. Cox multivariate proportional hazards regression model was used to estimate hazard ratios (HR) for all-cause and cancer, cardiovascular, diabetes or chronic kidney disease (CKD) as cause-specific mortality among patients with SPS. At an eGFR(CYS)/eGFR(CR)-ratio <0.70, the adjusted SPS death risk in the total cohort (HR 3.0, 95% CI 2.4-3.7) was clearly higher than that for the other diagnosis groups. In a sub-cohort of 1300 persons with or without diagnosis, but with normal mGFR, the all-cause mortality of SPS was markedly increased (HR 4.1, 95% CI 2.6-6.5). In a sub-cohort of 567 persons with normal mGFR and no diagnosis, the all-cause mortality of SPS was even more increased (HR 7.3, 95% CI 2.3-23). The prevalence of SPS in the total cohort was 23% and in the sub-cohorts 17 and 12%, respectively. As SPS is associated with a high mortality, occurs in the absence of reduced mGFR and albuminuria, it expands the spectrum of kidney disorders.