Understanding liver function tests
Your blood report shows: ALT 65 IU/L, AST 48 IU/L, Bilirubin 1.5 mg/dL, Albumin 3.6 g/dL. Doctor says "Your liver is slightly inflamed. We need to find out why." You're worried. What does this mean? Do you have liver disease? What should you do?
Liver function tests are deceptive. Unlike kidney disease (where eGFR directly measures function) or diabetes (where glucose directly measures control), liver tests are indirect measures of damage and function. The same elevated ALT could mean you had a hepatitis A infection three weeks ago (which will completely resolve), or it could mean early cirrhosis that will eventually require a liver transplant. Understanding which interpretation is correct requires understanding not just individual numbers but patterns and relationships between them.
Why the liver matters: Understanding its five critical jobs
Your liver is your body's most important chemical factory. It has over 500 functions, but five are absolutely critical:
1. Detoxification: Your liver breaks down toxins—medicines, alcohol, pesticides—into forms your kidneys can excrete. When liver fails, toxins accumulate (explaining the confusion and altered mental status in liver failure).
2. Bile production: Your liver makes bile, which breaks down fats in food. Without bile, you can't digest fats properly and become malnourished.
3. Protein synthesis: Your liver makes albumin (the main blood protein), clotting factors, and many other essential proteins. Low albumin indicates chronic liver disease.
4. Glucose regulation: Your liver stores glucose as glycogen and releases it when blood sugar drops. This is why liver disease causes low blood sugar and shakiness.
5. Immunity: Your liver breaks down bacteria and foreign substances that come from your gut through the portal vein. When liver fails, bacterial infections become common.
When liver function declines, all these jobs decline. You become malnourished, you bleed easily, your brain gets foggy, infections develop, and blood sugar drops unpredictably.
The five main liver tests
ALT (Alanine Aminotransferase): The liver-specific injury marker
ALT is an enzyme found almost exclusively in liver cells. When liver cells are injured, they release ALT into the bloodstream. Think of ALT as a "liver cell is damaged" alarm bell.
Normal ALT: 7-56 IU/L (varies slightly by lab and gender; males often slightly higher)
Mildly elevated: 55-150 IU/L Moderately elevated: 150-400 IU/L Markedly elevated: >400 IU/L (often >1000 in acute hepatitis)
Key insight: ALT is highly specific for liver. If ALT is elevated, you definitely have liver cell injury. The severity of elevation roughly correlates with severity of injury (though not perfectly—someone with chronic cirrhosis might have only mildly elevated ALT while someone with acute viral hepatitis might have ALT >5000).
AST (Aspartate Aminotransferase): The less specific marker
AST is found in liver, but also in muscles, heart, kidneys, and red blood cells. When you exercise hard, your AST goes up. When you have a heart attack, your AST goes up. When you have rhabdomyolysis (muscle breakdown), your AST goes up. This makes AST less specific for liver disease than ALT.
Normal AST: 10-40 IU/L
The ALT-to-AST ratio tells a story:
- ALT > AST (by a lot): Usually means viral hepatitis, fatty liver, or acetaminophen toxicity
- AST > ALT (marked): Usually means alcoholic liver disease or cirrhosis
- AST >> ALT (very marked): Could mean muscle injury, not liver injury
Example:
- Person A: ALT 80, AST 40 → Pattern suggests viral hepatitis or fatty liver, not alcoholic disease
- Person B: ALT 50, AST 140 → Pattern strongly suggests alcoholic liver disease
Bilirubin: The waste product that causes jaundice
Bilirubin is produced when red blood cells break down (after living ~120 days). Your liver processes bilirubin and excretes it through bile into the intestines, eventually appearing in stool (which is why stool is brown).
When liver is damaged, bilirubin can't be processed and accumulates in blood, causing jaundice (yellow skin and eyes), dark urine, pale stool.
Normal bilirubin ranges:
- Total: 0.1-1.2 mg/dL
- Direct (conjugated): 0.0-0.3 mg/dL
- Indirect (unconjugated): 0.1-1.0 mg/dL
What elevated total bilirubin means:
- If direct bilirubin is high: Cholestasis (bile backup). Causes include gallstones, biliary obstruction, or liver inflammation preventing bile excretion.
- If indirect bilirubin is high: Either red blood cells breaking down too fast (hemolysis) or liver not processing bilirubin well (hepatocellular injury).
Why this matters:
- Direct hyperbilirubinemia (>50% of total) suggests bile duct problem or severe hepatocellular disease
- Indirect hyperbilirubinemia suggests hemolysis or mild hepatocellular disease
- Rapidly rising bilirubin (normal to >3 in days) suggests acute hepatic necrosis (hepatitis, drug toxicity)
- Slowly rising bilirubin (over weeks) suggests chronic liver disease or obstruction
Albumin: The marker of chronic liver function
Albumin is the main protein in your blood. Your liver is the only organ that makes it. Unlike AST/ALT (which rise acutely when liver cells are injured), albumin falls slowly only after prolonged liver damage.
Normal albumin: 3.5-5.0 g/dL
Mildly low: 3.0-3.5 g/dL (suggests chronic liver disease or malnutrition) Moderately low: 2.5-3.0 g/dL (significant chronic liver disease) Severely low: <2.5 g/dL (advanced cirrhosis, imminent liver failure)
Why albumin is important:
- Acute hepatitis: ALT very high, but albumin remains normal (liver still making albumin)
- Cirrhosis: ALT might be only mildly elevated, but albumin is low (years of damage have exhausted the liver's synthetic capacity)
- Nutritional deficiency: Albumin low but liver enzymes normal (malnutrition, not liver disease)
ALP (Alkaline Phosphatase): The bile duct marker
ALP is an enzyme found in bile ducts and bone. When bile ducts are obstructed or inflamed, ALP rises into bloodstream.
Normal ALP: 40-150 IU/L (varies more by lab than other enzymes, and is higher in children and pregnant women)
Marked elevation: Usually indicates cholestasis (bile duct problem)
Why this matters:
- High ALP with high bilirubin + normal/low transaminases = Biliary obstruction (likely gallstone or tumor)
- High ALP with high transaminases = Hepatitis or cirrhosis with cholestasis
- Normal ALP with very high transaminases = Pure hepatocellular disease, no bile duct involvement
How to read a liver function report
Most Indian labs report like this:
LIVER FUNCTION TEST
Bilirubin (Total) : 0.9 mg/dL [Normal: 0.1-1.2]
Bilirubin (Direct) : 0.2 mg/dL [Normal: 0.0-0.3]
Bilirubin (Indirect) : 0.7 mg/dL [Normal: 0.1-1.0]
ALT (SGPT) : 48 IU/L [Normal: 7-56]
AST (SGOT) : 32 IU/L [Normal: 10-40]
ALP (Alkaline Phos) : 95 IU/L [Normal: 40-150]
Albumin : 4.1 g/dL [Normal: 3.5-5.0]
Total Protein : 6.8 g/dL [Normal: 6.0-8.3]
Red flags to notice:
- Bilirubin >3 (jaundice is becoming visible)
- ALT/AST >3x normal (significant injury)
- Albumin <3.5 (chronic disease)
- ALP very high (bile duct problem)
Understanding different patterns of liver disease
Pattern 1: Acute viral hepatitis
Typical values:
- ALT: 800-5000 IU/L (markedly elevated)
- AST: 500-3000 IU/L (elevated but usually less than ALT)
- Bilirubin: Normal early, then rises to 5-10 mg/dL
- Albumin: Normal (too acute to affect synthesis)
- ALP: Normal or mildly elevated
What it means:
- Acute infection (likely hepatitis A, B, or E)
- Massive liver cell injury occurring
- Liver function usually recovers if person survives acute phase (unless fulminant hepatic failure develops)
Timeline:
- Week 1: Enzymes rising rapidly, patient feels flu-like
- Week 2-3: Enzymes peak, jaundice appears
- Week 4-8: Enzymes fall, recovery begins (if no complications)
Pattern 2: Fatty liver disease (NAFLD)
Typical values:
- ALT: 40-100 IU/L (mildly elevated, usually <100)
- AST: 30-70 IU/L (less elevated than ALT)
- Bilirubin: Normal
- Albumin: Normal
- ALP: Normal or mildly elevated
What it means:
- Fat accumulation in liver cells
- Usually from obesity, diabetes, metabolic syndrome
- Usually reversible with weight loss and lifestyle change
- But can progress to cirrhosis if ignored (10-20% progress to advanced disease)
Important: Most people with elevated enzymes and normal bilirubin/albumin have simple fatty liver that improves with weight loss. This is not "liver disease" in the serious sense, but it needs attention to prevent progression.
Pattern 3: Alcoholic liver disease
Typical values:
- ALT: 40-100 IU/L (mildly elevated)
- AST: 80-200 IU/L (elevated more than ALT—classic alcoholic pattern)
- AST:ALT ratio: >2 (AST more than double ALT)
- Bilirubin: Normal to mildly elevated
- Albumin: Normal if acute, low if chronic
- ALP: Normal or mildly elevated
What it means:
- Chronic alcohol damage to liver
- If AST:ALT ratio >2, alcoholic liver disease is likely
- If albumin also low, suggests progression to cirrhosis
Timeline:
- Years 1-5 of heavy drinking: Fatty liver (reversible)
- Years 5-15: Alcoholic hepatitis (reversible if stop drinking)
- Years 15+: Cirrhosis (irreversible, requires transplant)
Pattern 4: Cirrhosis
Typical values:
- ALT: 30-80 IU/L (often surprisingly normal or only mildly elevated)
- AST: 40-150 IU/L (can be normal or elevated)
- Bilirubin: Normal early, then progressively elevated (often >2-3 in advanced cirrhosis)
- Albumin: <3.5 g/dL (low, indicating synthetic dysfunction)
- ALP: Often elevated
- Platelet count: Low (because cirrhotic liver doesn't produce thrombopoietin)
What it means:
- Advanced, mostly irreversible liver disease
- Liver function is failing (not just injured, but can't synthesize proteins or detoxify properly)
- High risk of variceal bleeding, ascites, hepatic encephalopathy
- Needs specialist management, possible transplant evaluation
Critical finding: Low albumin + elevated bilirubin + normal/low transaminases = This pattern is actually MORE serious than high transaminases because it indicates the liver has lost synthetic function, not just been injured.
Pattern 5: Biliary obstruction
Typical values:
- ALT: Mildly to moderately elevated (50-200)
- AST: Similar to ALT
- Bilirubin: Markedly elevated (often >4), mostly direct
- ALP: Very high (often >300)
- Albumin: Normal (acute obstruction hasn't had time to affect synthesis)
What it means:
- Bile duct blocked (likely gallstone, tumor, or stricture)
- Bilirubin can't be excreted, backs up into blood
- Usually requires imaging (ultrasound/CT) and possibly intervention (ERCP)
Timeline:
- If stone: Can be acute onset
- If tumor: Gradual progressive jaundice
Why patterns matter more than individual numbers
The same ALT of 60 IU/L could mean:
Scenario 1 - Recovering viral hepatitis:
- ALT: 60 (was 2000 last week)
- AST: 40
- Bilirubin: 3.5 (was 8 last week)
- Albumin: 4.0
- Interpretation: Getting better, no action needed except supportive care
Scenario 2 - Progressively worsening cirrhosis:
- ALT: 60 (was 50 last month, 40 three months ago)
- AST: 95 (rising)
- Bilirubin: 2.5 (was 1.5 last month)
- Albumin: 2.8 (was 3.2 last month)
- Interpretation: Worsening decompensation, needs urgent specialist evaluation
Medications that can damage your liver
Common medicines that cause liver injury:
Antibiotics: Amoxicillin-clavulanate, isoniazid, nitrofurantoin Pain relievers: Acetaminophen (>3000mg daily), NSAIDs in susceptible people Statins: Rarely, usually caught by monitoring Antituberculosis drugs: Rifampicin, INH, pyrazinamide Antiretrovirals: Particularly in HIV patients Herbal supplements: Greater celandine, kava, chaparral, others Steroids: Rare but documented
Prevention: Inform doctors of liver disease before taking new medicines. Avoid combining acetaminophen with alcohol. Monitor LFTs if on potentially hepatotoxic drugs.
Practical tracking of liver function
Create a tracking sheet if you have liver disease or abnormal enzymes:
LIVER FUNCTION TRACKING
Date | ALT | AST | Bili | Albumin | Symptoms | Status
Jan 2026 | 65 | 48 | 1.0 | 4.1 | No symptoms, fatigue | Mild hepatitis, investigating
Apr 2026 | 55 | 42 | 0.8 | 4.0 | Symptoms improving | Trending better
Jul 2026 | 42 | 38 | 0.7 | 4.1 | Back to normal | Resolution, maintain monitoring
Track this quarterly if abnormal, then annually once normalized.
FAQ
Q: I have ALT 65 IU/L and the lab says this is "normal" but my doctor says it's elevated. Who is right? A: Your doctor. Lab reference ranges vary and are often set too high. Many labs use upper normal of 40 for women and 56 for men. ALT >40 warrants investigation for cause.
Q: My ALT is elevated but I feel fine. Should I be worried? A: Not immediately worried, but investigate the cause. Many serious liver diseases (viral hepatitis, cirrhosis, fatty liver) are asymptomatic in early stages. Symptoms only appear when disease is advanced.
Q: What does it mean if my AST is higher than my ALT? A: If AST:ALT ratio >2, think about alcoholic liver disease or cirrhosis. Both are serious and need investigation.
Q: Can I have normal liver tests and still have liver disease? A: Yes. Early cirrhosis can have near-normal enzymes. Chronic hepatitis C can have normal enzymes. This is why screening tests (platelet count, albumin) are important.
Q: Do I need a liver biopsy if my enzymes are elevated? A: Not always. Modern liver stiffness testing (FibroScan/transient elastography) can assess fibrosis without biopsy. Biopsy reserved for when diagnosis unclear or when cirrhosis suspected.
Q: How often should my liver tests be checked? A: If abnormal: 2-4 weeks later for follow-up. If normal: Every 1-2 years if risk factors (hepatitis, heavy alcohol use, medications). If established liver disease: Every 3-6 months.
Q: What happens if bilirubin keeps rising? A: If bilirubin >3, that's visible jaundice and needs urgent evaluation. If >10, that's severe and suggests either massive hepatocellular necrosis (acute hepatitis) or complete biliary obstruction.
Key takeaway
Your liver is a quiet organ. By the time you have symptoms (jaundice, ascites, confusion), liver disease is often advanced. This is why abnormal liver tests discovered on routine screening are valuable—they catch disease when still reversible. Understand your liver numbers. Track trends over time. If ALT, AST, or bilirubin are elevated, find the cause (ultrasound, hepatitis serologies, imaging). Most causes are treatable or preventable with lifestyle changes if caught early.