Liver Function Test (LFT) – Complete Guide

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🧪 Liver Function Test (LFT) – Complete Guide | Normal Values & Causes 🧪 Liver Function Test (LFT) – Complete Guide
📖 BLOG #12 · APRIL 2025

🧪 Liver Function Test (LFT) – Complete Guide

Everything you need to know about LFT: enzymes, proteins, bilirubin & clinical interpretation.

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1️⃣ Introduction

The Liver Function Test (LFT) is a panel of blood tests that evaluate the health of your liver. It measures enzymes, proteins, and bilirubin to detect inflammation, damage, or dysfunction. LFTs are essential for diagnosing hepatitis, fatty liver, cirrhosis, alcohol-related injury, and monitoring medication side effects. This guide unpacks each component, normal ranges, and clinical patterns.

2️⃣ Components of LFT

🧬 Core 7 markers
🟢ALT (Alanine Transaminase)
🔵AST (Aspartate Transaminase)
🟡ALP (Alkaline Phosphatase)
🟠Bilirubin (Total)
🔶Bilirubin (Direct)
⚪Albumin
🔘Total Protein

ALT & AST: enzymes from liver cells; leak into blood during injury.
ALP: related to bile ducts; rises in obstruction.
Bilirubin: waste product from RBC breakdown; direct (conjugated) & indirect.
Albumin & Total protein: synthetic function; low levels indicate chronic disease.

3️⃣ Normal Values Table

Component Normal Range (Adult) Unit
ALT7 – 55U/L
AST8 – 48U/L
ALP40 – 130U/L
Bilirubin (Total)0.1 – 1.2mg/dL
Bilirubin (Direct)0.0 – 0.3mg/dL
Albumin3.5 – 5.0g/dL
Total Protein6.0 – 8.3g/dL

📌 Reference ranges may vary slightly between labs.

4️⃣ High LFT Causes

⬆️ Elevated enzymes & bilirubin

  • ALT/AST Viral hepatitis (A, B, C), NAFLD, alcohol-related liver disease, drug toxicity (acetaminophen), ischemia.
  • ALP Bile duct obstruction (stones, stricture), primary biliary cholangitis, infiltrative liver disease, bone growth (physiological).
  • Bilirubin Pre-hepatic (hemolysis), hepatic (Gilbert’s, hepatitis), post-hepatic (obstruction).
  • GGT* (often co-tested) Alcohol use, enzyme induction.
💡 Pattern recognition: ALT > AST suggests viral/NAFLD; AST > ALT often alcohol related; isolated ALP elevation → think cholestasis.

5️⃣ Low LFT Causes

⬇️ Decreased levels – what they mean

  • Albumin ↓ Chronic liver disease (cirrhosis), malnutrition, nephrotic syndrome, protein-losing enteropathy.
  • Total Protein ↓ Advanced liver disease, overhydration, malabsorption.
  • Low ALT/AST (rare) Sometimes seen in uremia, pyridoxine deficiency, or chronic dialysis; not usually clinically significant.

⚠️ Persistently low albumin is a marker of poor prognosis in cirrhosis.

6️⃣ Clinical Importance

🏥

Why LFT is indispensable:

  • Screen for silent liver disease (NAFLD, hepatitis B/C).
  • Monitor progression of cirrhosis and alcoholic liver disease.
  • Evaluate jaundice – differentiate pre-hepatic, hepatic, cholestatic.
  • Track hepatotoxicity from medications (statins, amiodarone, TB drugs).
  • Assess synthetic function (albumin, INR) – guides prognosis (MELD score).

7️⃣ FAQ Section

❓ Can I drink water before LFT?
Yes, water is allowed. Fasting for 8–12 hours is often recommended for accurate lipids, but LFT can be non-fasting. Some labs prefer fasting to avoid lipemia interference.
❓ What is the most important LFT value?
No single marker — they are interpreted together. ALT is liver-specific; albumin reflects synthetic capacity; bilirubin indicates excretion.
❓ Can dehydration affect LFT?
Mildly; dehydration may slightly concentrate proteins, but usually not significantly. Severe dehydration may elevate enzymes due to stress.
❓ Are AST and ALT always high in fatty liver?
Often mildly elevated (2-3x ULN), but normal enzymes do not rule out fatty liver. Imaging is more sensitive for steatosis.
❓ What medications falsely elevate LFT?
Acetaminophen (high dose), statins, some antibiotics (isoniazid, nitrofurantoin), anticonvulsants, and even some herbs (kava, comfrey).
❓ What does a high direct bilirubin mean?
Direct (conjugated) bilirubin rises in obstructive jaundice (stones, strictures, malignancy) or hepatocellular injury with cholestasis.
📌

Liver health quick tips

🥗 Maintain healthy weight
🍷 Limit alcohol
💉 Get vaccinated (Hep B)
💊 Avoid unnecessary meds
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💬 Bottom line: Liver Function Test is a powerful, cost-effective screening tool. Interpretation requires correlation with history, imaging, and sometimes additional tests. Always discuss abnormal results with your clinician.

🧪 Blog #12 – Liver Function Test Complete Guide

© 2025 LABORATORY GUIDE· All rights reserved · For informational purposes only, not medical advice.

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