What is the function of the albumin (A) to globulin (G) ratio?

The Function of Albumin Globulin Ratio (A/G Ratio)

The albumin to globulin (A/G) ratio is a valuable clinical marker that assesses liver function, protein metabolism, and serves as a prognostic indicator for various diseases including liver disorders, kidney disease, heart failure, and certain cancers. 1

Clinical Significance and Mechanism

• The A/G ratio represents the relationship between serum albumin and globulin proteins, providing insights into liver function even when individual protein values remain within normal ranges 1
• In liver disease, the ratio typically decreases as albumin production falls while globulins increase compensatorily, making it particularly useful for liver function assessment 1
• The ratio provides more stable information than individual protein values alone since both albumin and globulin can be affected by hydration status 1

Clinical Applications

Liver Disease Assessment

• The A/G ratio helps evaluate liver function and disease progression, as recommended by the American Gastroenterological Association 1
• In hepatic diseases, decreased albumin with compensatory globulin rise occurs in approximately 72.3% of cases, compared to only 32.3% in non-hepatic systemic diseases 2
• The ratio serves as an early indicator of liver dysfunction before individual protein values fall outside normal ranges 1

Kidney Disease Evaluation

• The A/G ratio provides complementary information when used alongside albumin-to-creatinine ratio (ACR) and estimated glomerular filtration rate (eGFR) in kidney disease assessment 1, 3
• It helps contextualize protein metabolism changes in kidney disorders, particularly in conditions affecting serum protein levels 1

Prognostic Value in Various Conditions

• The A/G ratio serves as an independent predictor of mortality in chronic heart failure patients, with lower ratios associated with poorer outcomes 4
• In cancer patients, particularly those with small-cell lung cancer and hepatocellular carcinoma, the pretreatment A/G ratio has demonstrated significant prognostic value 5, 6
• A lower A/G ratio has been associated with increased mortality risk in heart failure patients with reduced ejection fraction (HFrEF) 4

Alternative Measurements and Interpretations

• The Globulin Compensation Index (GCI) has been developed as an alternative to the A/G ratio to better measure changes in serum globulins when albumin is decreased, calculated as: GCI = (G - 25) / (35 - SA) 2
• Low calculated globulin (total protein - albumin) levels can be used as a screening test for antibody deficiency, with values below 18 g/L (using bromocresol green methodology) detecting patients with IgG levels below 6 g/L in 89% of cases 7

Interpretation Considerations and Limitations

• The A/G ratio should always be interpreted in context with other laboratory findings and clinical presentation 1
• In conditions like nephrotic syndrome, both albumin and globulins may decrease simultaneously, potentially limiting the ratio's reliability without additional clinical context 1
• Factors affecting albumin or globulin levels independently (such as hydration status, thyroid function, obesity) can influence the ratio and should be considered during interpretation 8, 1
• Thyroid hormones can affect albumin metabolism, with hyperthyroidism potentially lowering values and hypothyroidism potentially increasing them 8