What is the significance of the R ratio in patients with liver disease, particularly cirrhosis?

R Ratio in Liver Disease

The R ratio is a prognostic scoring system originally developed to predict survival following TIPS procedures in cirrhotic patients, calculated using creatinine, bilirubin, INR, and etiology of cirrhosis to stratify mortality risk. 1

Formula and Calculation

The R ratio is calculated using the following equation 1:

R = 0.9576 × log_e(creatinine mg/dL) + 0.3786 × log_e(bilirubin mg/dL) + 1.1206 × log_e(INR) + 0.6436 × (cause of cirrhosis)

Where:

• Creatinine and bilirubin must be in mg/dL (old units) 1
• Cause of cirrhosis is coded as 0 for alcoholic or cholestatic liver diseases and 1 for other causes 1

Clinical Significance and Risk Stratification

The R ratio was originally developed as part of the Model for End-Stage Liver Disease (MELD) scoring system to predict survival following TIPS procedures 1. The score provides clear mortality predictions:

Survival Predictions After TIPS 1:

• R > 1.8: Median survival of 3 months after elective TIPS; patients are considered unsuitable for the procedure unless being bridged to liver transplantation
• R = 1.5: Median survival of 6 months
• R = 1.3: Median survival of 12 months

Application in TIPS Decision-Making

TIPS insertion should be considered for patients requiring frequent paracentesis (generally >3 per month) with appropriate risk-benefit assessment using the R ratio. 1 The R ratio helps identify patients at high risk for poor outcomes:

• Patients with R > 1.8 should not undergo elective TIPS unless it serves as a bridge to transplantation 1
• Advanced Child-Pugh class C patients have less favorable outcomes with TIPS regardless of R ratio 1
• Hepatic encephalopathy occurs in approximately 25% of patients post-TIPS, with higher risk in those over 60 years 1

Evolution to Modern MELD Score

The R ratio evolved into the contemporary MELD score, which has become the standard prognostic model in cirrhosis 1. While the original R ratio incorporated etiology of cirrhosis, modern MELD scoring focuses primarily on objective laboratory values (creatinine, bilirubin, INR) 1.

Clinical Context and Limitations

When assessing liver function for major interventions like hepatic resection, the MELD score (derived from the R ratio concept) should be combined with other parameters including portal hypertension assessment, liver stiffness measurement, and indocyanine green kinetics. 1

Important Caveats:

• The R ratio uses old units (mg/dL) for creatinine and bilirubin, which must be converted if using SI units 1
• Renal dysfunction in cirrhotic patients with ascites leads to greater morbidity and is associated with prolonged ICU and hospital stays post-transplant 1
• The development of ascites itself carries a 50% mortality within 2 years, and refractory ascites carries 50% mortality within 6 months 1