Background Shrunken pore syndrome (SPS) as a novel phenotype of renal dysfunction is characterized by a difference in renal filtration between cystatin C and creatinine. The manifestation of SPS was defined as a cystatin C-based estimated glomerular filtration rate (eGFR) <60% of the creatinine-based eGFR. SPS has been shown to be associated with the progression and adverse prognosis of various cardiovascular and renal diseases. However, the predictive value of SPS for contrast-associated acute kidney injury (CA-AKI) and long-term outcomes in patients undergoing percutaneous coronary intervention remains unclear. Methods and Results We retrospectively observed 5050 consenting patients from January 2012 to December 2018. Serum cystatin C and creatinine were measured and applied to corresponding 2012 and 2021 Chronic Kidney Disease Epidemiology Collaboration equations, respectively, to calculate the eGFR. Chronic kidney disease (CKD) was defined as a creatinine-based eGFR <60 mL/min per 1.73 m² without dialysis. CA-AKI was defined as an increase in serum creatinine ≥50% or 0.3 mg/dL within 48 hours after contrast medium exposure. Overall, 649 (12.85%) patients had SPS, and 324 (6.42%) patients developed CA-AKI. Multivariate logistic regression analysis indicated that SPS was significantly associated with CA-AKI after adjusting for potential confounding factors (odds ratio [OR], 4.17 [95% CI, 3.17-5.46]; P<0.001). Receiver operating characteristic analysis indicated that the cystatin C-based eGFR:creatinine-based eGFR ratio had a better performance and stronger predictive power for CA-AKI than creatinine-based eGFR (area under the curve: 0.707 versus 0.562; P<0.001). Multivariate logistic analysis revealed that compared with those without CKD and SPS simultaneously, patients with CKD and non-SPS (OR, 1.70 [95% CI, 1.11-2.55]; P=0.012), non-CKD and SPS (OR, 4.02 [95% CI, 2.98-5.39]; P<0.001), and CKD and SPS (OR, 8.62 [95% CI, 4.67-15.7]; P<0.001) had an increased risk of CA-AKI. Patients with both SPS and CKD presented the highest risk of long-term mortality compared with those without both (hazard ratio, 2.30 [95% CI, 1.38-3.86]; P=0.002). Conclusions SPS is a new and more powerful phenotype of renal dysfunction for predicting CA-AKI than CKD and will bring new insights for an accurate clinical assessment of the risk of CA-AKI.

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