J-shaped relationship between serum creatinine and mortality in Korean patients with acute heart failure.

Background: Cachexia and sarcopenia are common among heart failure (HF) patients and are linked to poor outcomes. As serum creatinine levels are influenced by both renal function and muscle mass, our study aimed to investigate the relationship between serum creatinine levels and mortality in acute HF patients.

Methods: We enrolled 5198 consecutive acute HF patients from the Korea Acute Heart Failure (KorAHF) registry, excluding those on renal replacement therapy. Patients were categorized into five groups based on their discharge serum creatinine levels: low (< 0.6 mg/dL), reference (0.6-0.89 mg/dL), upper normal (0.9-1.19 mg/dL), high (1.2-1.49 mg/dL), and very high (≥ 1.5 mg/dL). The primary endpoint was post-discharge all-cause mortality.

Results: The mean creatinine level was 1.20 ± 0.88 mg/dL. Notably, 335 (6.4%) patients had serum creatinine levels < 0.6 mg/dL. These patients were younger (mean age, 67 years) and more likely to have a low BMI (< 18.5 kg/m²) compared to the reference group (15.3% vs. 6.4%). Over a median follow-up of 975 days, 1743 (34.8%) patients died. We observed a J-shaped relationship between serum creatinine levels and mortality, with both low and high levels associated with increased mortality. After adjusting for covariates, including age, sex, body mass index, diabetes, hypertension, smoking, malignancy, atrial fibrillation on electrocardiography, levels of C-reactive protein, sodium, hemoglobin, albumin, brain natriuretic peptide, de novo heart failure, use of beta-blockers, renin-angiotensin system inhibitors, and mineralocorticoid receptor antagonists, patients with serum creatinine levels < 0.6 mg/dL had a 33% higher risk of all-cause mortality (HR, 1.33; 95% CI, 1.06 to 1.66) compared to those with levels of 0.6-0.89 mg/dL. However, BUN, which is not affected by muscle metabolism, exhibited a linear relationship with mortality.

Conclusions: Among acute HF patients, there exists a J-shaped relationship between discharge serum creatinine levels and mortality, highlighting the increased mortality risk in individuals with very low serum creatinine levels.