Creatinine production rate is an integrative indicator to monitor muscle status in critically ill patients.

Summary

Across animal and clinical studies (n=629 ICU patients), creatinine production rate (CPR) reflected both skeletal muscle quantity and quality, decreased with systemic inflammation, correlated with muscle cross-sectional area, and lower baseline CPR index independently predicted one-year mortality. CPR trajectories were multifactorial and not uniformly declining, indicating sensitivity to metabolic derangements beyond muscle loss.

Key Findings

• In animals, CPR depended on muscle volume, creatine content, and metabolic status; systemic inflammation reduced CPR.
• In 629 ICU patients, admission CPR index strongly correlated with muscle cross-sectional area and independently predicted one-year mortality.
• Percent change in CPR weakly tracked muscle CSA changes, and acute CPR trajectories were nonuniform, indicating multifactorial influences beyond muscle loss.

Clinical Implications

CPR could be incorporated into ICU workflows to risk-stratify patients, track anabolic/catabolic states, and guide nutrition and rehabilitation strategies beyond traditional creatinine-based assessments.

Limitations

• Observational clinical analyses susceptible to confounding and practice variability
• Renal function fluctuations and fluid shifts may affect CPR independent of muscle biology

Future Directions

Prospective interventional studies to test CPR-guided nutrition/rehabilitation protocols and to standardize measurement timing; validate in perioperative cohorts.