Interpreting LFT Patterns

Abnormal liver function tests (LFTs) are extremely common in the NHS.
Most are benign or chronic, but some indicate serious liver disease that needs urgent action.

This guide focuses on how to interpret LFTs quickly and safely on the ward, using patterns rather than memorising causes.

✅ First principle (most important)

Never read LFTs number by number.

Always ask:

What pattern does this fit?

Because management depends on the pattern, not the exact values.

✅ Step 1 – Know what each test actually means

Don’t memorise numbers — understand what they reflect.

ALT / AST → Hepatocellular injury

Leak out when liver cells are damaged.

Think:
👉 inflammation or injury

Examples:

  • Hepatitis
  • Fatty liver
  • Alcohol
  • Drugs

ALP → Cholestasis/obstruction

Raised when bile flow is blocked.

Think:
👉 obstruction or bile duct disease

Examples:

  • Gallstones
  • Cholangitis
  • PSC/PBC
  • Tumour

Bilirubin → Excretion function

Raised when:

  • Liver can’t process bile
  • Or obstruction
  • Or haemolysis

Think:
👉 jaundice severity

Albumin & INR → Synthetic function

Reflect liver’s ability to make proteins.

Think:
👉 how well the liver is working

Very important:

Abnormal synthetic function = serious disease

✅ Step 2 – Identify the pattern

This is the key clinical step.

There are only 3 main patterns.

🟡 Pattern 1 – Hepatocellular

Labs:

  • ALT/AST ↑↑
  • ALP mild/normal

Think:

👉 Liver cell injury

Common causes (practical list)

  • Viral hepatitis
  • Alcohol-related liver disease
  • MASLD
  • Drug-induced liver injury
  • Autoimmune hepatitis
  • Ischaemic hepatitis (“shock liver”)

Ward thinking:

ALT much higher than ALP → think hepatitis

🟢 Pattern 2 – Cholestatic

Labs:

  • ALP ↑↑
  • ALT mild

Think:

👉 Bile flow problem

Common causes

  • Gallstones
  • Cholangitis
  • Obstruction
  • PSC / PBC
  • Malignancy
  • Drug-induced cholestasis

Ward thinking:

ALP much higher than ALT → think obstruction → image the biliary tree

Usually → ultrasound first

🔴 Pattern 3 – Synthetic failure

Labs:

  • Low albumin
  • High INR
  • ± bilirubin

Think:

👉 Liver not functioning properly

This is the most serious pattern.

Common causes

  • Cirrhosis
  • Acute liver failure
  • Severe hepatitis
  • Sepsis

Ward thinking:

Abnormal INR/albumin = sick liver → escalate early

These patients are high risk.

✅ Step 3 – Add clinical context

LFTs never interpreted alone.

Always combine with:

  • History (alcohol, drugs, infection)
  • Symptoms (pain, jaundice, fever)
  • Observations
  • Imaging

Pattern + story = diagnosis

✅ Practical examples (how you think on-call)

Scenario 1

ALT 650
ALP 120

👉 Hepatocellular
→ think viral/drug/alcohol/AIH

Scenario 2

ALP 500
ALT 70
Jaundice

👉 Cholestatic
→ urgent ultrasound → obstruction?

Scenario 3

Albumin 22
INR 2.0
Known cirrhosis

👉 Synthetic failure
→ decompensation → escalate

Scenario 4

AST > ALT (2:1)
Alcohol history

👉 Alcohol-related

Classic exam + ward pattern

Scenario 5

ALT > AST
Overweight/diabetic

👉 MASLD likely

✅ Useful quick clues juniors should know

AST:ALT ratio > 2

→ Alcohol-related disease

Very high ALT/AST (>1000)

→ Acute hepatitis or ischaemia
(not chronic disease)

Isolated raised ALP

→ Think cholestasis or bone
(check GGT to confirm liver source)

Low albumin alone

→ Could be malnutrition or chronic illness
(not always liver failure)

Rising INR

→ Red flag
Always take seriously

✅ When to escalate urgently

Refer/escalate if:

  • INR rising
  • Confusion/encephalopathy
  • Jaundice + sepsis
  • Suspected acute liver failure
  • Very abnormal LFTs with systemic illness
  • NEWS ≥5

These are not “routine LFT abnormalities”.

❌ Common mistakes juniors make

  • Looking at numbers individually
  • Panicking over mild ALT rises
  • Missing synthetic failure
  • Not imaging cholestatic pattern
  • Not checking drug history
  • Over-investigating trivial abnormalities

Always think pattern first.

✅ Simple ward algorithm

When you see abnormal LFTs:

Ask:

  1. ALT or ALP predominant?
  2. Is synthetic function abnormal?
  3. Does the history fit?
  4. Do I need imaging or escalation?

That’s it.

✅ Take-home concept

Don’t memorise causes — recognise patterns.
ALT = hepatocellular, ALP = cholestatic, INR/albumin = severity.

If you can do that, you’ll interpret 90% of LFTs safely.