Left-digit bias in serum creatinine levels and contrast administration: a nationwide cohort study using a Japanese percutaneous coronary intervention registry

Background Contemporary quality initiatives emphasize minimizing contrast volume as a key modifiable factor for preventing acute kidney injury (AKI) following percutaneous coronary intervention (PCI). Left-digit bias, a cognitive bias in which the leftmost digit of continuous variables disproportionately influences decisions, may unintentionally affect contrast administration by truncating serum creatinine values. The potential impact of left-digit bias in serum creatinine level on contrast volume in PCI was assessed. Methods Among patients undergoing PCI between January 2018 and December 2022 in the Japanese nationwide prospective multicenter registry, the primary outcome of PCI contrast volume was assessed by comparing contrast volume differences at integer creatinine thresholds (e.g., 1.0 mg/dL and 2.0 mg/dL). AKI risks were calculated by a validated risk scoring system. Results Among 735,696 PCI procedures, the median contrast volume was 117 mL (interquartile range 85-157 mL). Average contrast volumes revealed sharp decreases at baseline creatinine levels above vs. less than 1 mg/dL (mean difference = 2.2 mL [95% CI = 1.6, 2.8]) and 2 mg/dL (4.7 [1.6, 7.8]), but not at 3 mg/dL (-2.0 [-10.0, 6.0]) (Abstract Picture 1). Despite differences at integer thresholds of creatinine, minimal variation across AKI risk levels suggests that operators prioritize discrete creatinine values over predicted AKI risk. Conclusion Over-reliance on creatinine values may lead to inappropriate contrast administration, especially in high-risk patients with less elevated creatinine levels. Formal risk stratification should be used to optimize contrast use for AKI prevention.