8 Facts to Help Master the Interpretation of Liver Chemistry Tests
Elevated liver tests? Don't panic!
This thread will give you a structured approach to interpreting LFTs, differentiating patterns of injury, and knowing when to worry.
- Thread 🧵
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Check out our blog post to learn more details about each fact!
pointofcaremedicine.com/blog-post/liver-chemistry-tests
TL;DR
Hepatocellular vs. Cholestatic
Injury Patterns:
- Hepatocellular: AST/ALT >> Alk Phos
- Cholestatic: Alk Phos >> AST/ALT
Use the R ratio to quantify:
R = (ALT/ALT ULN) / (ALP/ALP ULN).
- R > 5 = hepatocellular
- R < 2 = cholestatic
- 2-5 = mixed.
AST, ALT, and the R Ratio
ALT is more specific for hepatocellular injury (AST is also in muscle, heart, etc.).
AST/ALT > 2:1 suggests alcoholic liver disease
In viral hepatitis/NAFLD, ALT > AST. This reverses in cirrhosis of any cause!
Redefining "Normal" ALT
True Normal ALT: Much lower than lab ranges!
Optimal ULN: 29-33 U/L (males), 19-25 U/L (females).
Elevated ALT (even slightly) correlates with increased liver-related mortality.
Magnitude Matters
Systematic Approach:
<2x ULN: NAFLD, EtOH, meds, chronic viral hepatitis
2-5x ULN: Add hemochromatosis, autoimmune hepatitis, Wilson's, A1AT
5-15x ULN: Consider acute viral hepatitis (A, B, C)
>15x ULN: Acetaminophen, ischemic hepatopathy, autoimmune hepatitis.
Cholestatic Injury
First, confirm hepatic origin of Alk Phos with GGT or fractionation of isoenzyme
Next steps:
- Ultrasound 1st line to r/o biliary obstruction
- (+) Anti-mitochondrial Ab = Primary Biliary Cholangitis (PBC)
- "Beaded" bile ducts on MRCP/ERCP = Primary Sclerosing Cholangitis (PSC)
Bilirubin Breakdown
Elevated direct bilirubin = hepatocellular/biliary obstruction.
Isolated unconjugated = Gilbert's or hemolysis.
Gilbert's: benign, <4 mg/dL, increases w/ fasting
Hemolysis: Rarely bilirubin >5 mg/dL (unless co-existing liver/renal dx). Check hapto, LDH, retic count.
Medications (DILI)
Drugs & the Liver: Consider meds in every LFT abnormality.
Common culprits:
- Abx
- Antiepileptics
- NSAIDs
- Statins
- Anti-TB
- Antiretrovirals.
Always ask about herbal supplements (i.e green tea extract) and alternative medicines.
Red Flags: When to Worry
Albumin and PT/INR abnormalities = impaired hepatic synthetic function = more severe disease.
Acute Liver Failure: Acute liver injury + coagulopathy (INR >1.5) + encephalopathy = urgent referral for transplant.
Liver Function: More Than Just LFTs
- Albumin & PT/INR tell the real story. Albumin half life = 3 wks - so lowe levels suggests a more chronic process.
- Prolonged PT is more acute and can be prolonged within 24 hours of injury!
Physical Exam:
- Chronic Liver Disease Stigmata: Jaundice, ascites, splenomegaly, palmar erythema, spider angiomata.
- Firm liver edge (cirrhosis/infiltration), enlarged nodular liver (malignancy).
- Dupuytren's (EtOH), Kayser-Fleischer rings (Wilson's), bronzed skin (hemochromatosis).
Source:
Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol. 2017 Jan;112(1):18-35. doi: 10.1038/ajg.2016.517. Epub 2016 Dec 20. PMID: 27995906
pubmed.ncbi.nlm.nih.gov/27995906/
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