Importance of SGOT and SGPT in Liver Disease
SGOT (AST) and SGPT (ALT) are essential biomarkers for detecting liver injury and should be included in the initial investigation of potential liver disease, though their primary value lies in identifying hepatocellular damage rather than predicting disease severity or fibrosis stage. 1
Primary Diagnostic Role
Initial screening for liver disease should include ALT, along with bilirubin, albumin, alkaline phosphatase (ALP), and GGT, plus a complete blood count. 1 The British Society of Gastroenterology's BALLETS study demonstrated that ALT and ALP identified the vast majority of adults with liver disease. 1
Key Diagnostic Patterns
AST elevation occurs in all forms of alcoholic liver disease with 50% sensitivity and approximately 80% specificity, though levels rarely exceed 300 IU/mL. 1
The AST/ALT ratio is diagnostically significant: A ratio >1 is typical in alcoholic liver disease 1, while a ratio >2 is highly suggestive of alcoholic hepatitis and cirrhosis, occurring in 70% of these patients compared to only 26% with postnecrotic cirrhosis. 2
ALT is more specific for liver injury than AST, as AST is also found in cardiac muscle, skeletal muscle, kidneys, and red blood cells, whereas ALT is predominantly hepatic. 1
Limitations in Clinical Practice
Both AST and ALT correlate poorly with histological severity of liver disease, and approximately 50% of patients with chronic HCV infection have normal transaminase values despite having significant histological liver disease. 1 This represents a critical pitfall—normal transaminases do not exclude advanced fibrosis or cirrhosis. 1
Transaminase levels fluctuate over time, limiting their value for monitoring disease progression. 1
In alcoholic liver disease, the sensitivity of AST for detecting daily ethanol consumption >50g is only 50%, compared to 73% for GGT, making AST less useful as a screening tool for alcohol consumption. 1
Role in Fibrosis Assessment
The AST/ALT ratio helps assess fibrosis risk in adults: A ratio >1 indicates advanced fibrosis or cirrhosis, and this utility persists even when both values are within the normal reference interval. 1 However, this approach has not been validated in children. 1
- AST is incorporated into non-invasive fibrosis scores such as the AST to platelet ratio index (APRI), though APRI showed limited utility in alcoholic liver disease with only 13.2% sensitivity for significant fibrosis. 1
Monitoring Advanced Disease
In patients with advanced liver disease, AST and ALT should be measured at least every 6 months as part of comprehensive liver function testing and physical examination. 3
- Advanced alcoholic liver disease is suspected when transaminases are elevated alongside decreased albumin, prolonged prothrombin time, increased bilirubin, or thrombocytopenia. 1
Critical Clinical Pitfalls
Do not rely solely on transaminase levels to exclude liver disease—cirrhosis can exist with completely normal biochemistry, particularly in alcohol-related disease. 3 The ALFIE study showed that although abnormal AST or ALT predicted liver disease (HR=4.2), only 3.9% of those with abnormal values were diagnosed with significant liver disease within 5 years. 1
Extreme AST elevations (>5 times normal) with very high AST/ALT ratios should prompt consideration of non-alcoholic causes of hepatocellular necrosis, even in alcoholic patients, as this pattern can occur with acetaminophen hepatotoxicity. 4
Baseline Testing Indications
Baseline AST or ALT measurement is indicated before initiating treatment for latent tuberculosis infection in patients with HIV infection, pregnant women, those in the immediate postpartum period, persons with history of chronic liver disease (hepatitis B or C, alcoholic hepatitis, cirrhosis), regular alcohol users, and those at risk for chronic liver disease. 1