I am a healthy adult with Aspartate aminotransferase 34 U/L and Alanine aminotransferase 42 U/L, no symptoms, no known liver disease, and no recent hepatotoxic drug or alcohol exposure—are these results normal and what should I do?

Mildly Elevated Liver Enzymes: Assessment and Management

Your AST of 34 U/L and ALT of 42 U/L represent mild elevations that warrant systematic evaluation but do not require urgent intervention. These values fall into the category of mild elevation (<5× upper limit of normal), and given your lack of symptoms or known risk factors, the most likely causes are nonalcoholic fatty liver disease (NAFLD), transient physiological variation, or unrecognized metabolic risk factors. 1

Understanding Your Results

Your enzyme pattern shows:

• ALT (42 U/L) is mildly elevated above the sex-specific upper limit of normal (19-25 U/L for women, 29-33 U/L for men) 1
• AST (34 U/L) is at or just above the upper limit depending on your sex 1
• **AST:ALT ratio <1** (34/42 = 0.81), which is the characteristic pattern of NAFLD rather than alcoholic liver disease (which typically shows AST:ALT >2) 2, 3

Important context: Up to 38% of adults with initially elevated bilirubin and 31-36% with elevated ALT/AST will have normal values when retested within 2-4 weeks due to natural intraindividual variability. 4 This high variability means your first step should be confirmation rather than extensive workup.

Immediate Next Steps

Week 0-2: Confirm the Elevation

• Repeat ALT, AST, and a complete liver panel (including alkaline phosphatase, GGT, total and direct bilirubin, albumin, and PT/INR) in 2-4 weeks to establish whether this is persistent or transient 1
• If values normalize or decrease on repeat testing, no further immediate investigation is needed 1

Week 2-4: Initial Evaluation (if elevation persists)

Laboratory testing should include: 1

• Viral hepatitis serologies (HBsAg, anti-HBc IgM, anti-HCV) to exclude chronic viral hepatitis
• Metabolic parameters: fasting glucose or HbA1c, fasting lipid panel to assess for metabolic syndrome components
• Iron studies (ferritin, transferrin saturation) to screen for hemochromatosis
• Creatine kinase (CK) to exclude muscle injury as a source, particularly if you've engaged in recent intensive exercise 1, 2

Risk stratification: 1

• Calculate your FIB-4 score using age, ALT, AST, and platelet count
  • Score <1.3 (or <2.0 if age >65): Low risk for advanced fibrosis (≥90% negative predictive value)
  • Score >2.67: High risk requiring hepatology referral

First-line imaging: 1

• Abdominal ultrasound (sensitivity 84.8%, specificity 93.6% for moderate-to-severe hepatic steatosis) to identify:
  • Hepatic steatosis (fatty liver)
  • Biliary obstruction or structural abnormalities
  • Focal liver lesions

Most Likely Causes in Your Scenario

Given your profile (healthy, asymptomatic, no known liver disease, no hepatotoxic exposures):

1. Nonalcoholic fatty liver disease (NAFLD) – Most common cause affecting 20-30% of the general population, typically presents with AST:ALT <1 and mild elevations 2, 1

2. Transient physiological variation – Normal fluctuation that resolves on repeat testing 4

3. Unrecognized metabolic risk factors – Prediabetes, dyslipidemia, or central obesity may be present without your awareness 1

4. Recent vigorous exercise – Can transiently elevate AST more than ALT due to muscle origin 2

When to Escalate

Refer to hepatology if: 1

• ALT remains elevated ≥6 months without identified cause
• ALT increases to >5× ULN (>145-165 U/L for males, >95-125 U/L for females)
• Evidence of synthetic dysfunction (low albumin, elevated INR)
• FIB-4 score >2.67

Repeat testing within 2-5 days if: 1

• ALT increases to 2-3× ULN on follow-up

Common Pitfalls to Avoid

• Don't assume mild elevation is benign without proper evaluation – Even modest increases can reflect significant pathology, especially in women whose normal ALT range is lower 1
• Don't overlook non-hepatic causes – AST can be elevated from cardiac muscle, skeletal muscle, kidney disorders, or hemolysis 2
• Don't rely on ALT magnitude alone to predict disease severity – Normal ALT does not exclude significant liver disease; up to 50% of NAFLD patients and 10% with advanced fibrosis may have normal ALT 1
• Don't forget to calculate FIB-4 score – This simple tool identifies patients needing urgent specialist assessment 1

Bottom Line

Repeat your liver enzymes in 2-4 weeks. 1 If they remain elevated, proceed with the systematic evaluation outlined above, focusing on metabolic risk factors and obtaining an abdominal ultrasound. The vast majority of cases like yours represent either transient variation or early NAFLD, both of which are manageable with lifestyle modification if metabolic risk factors are present. Your normal synthetic function (implied by lack of symptoms) and mild elevation pattern suggest you are not at immediate risk, but confirmation and identification of the underlying cause are important for long-term health.