Overview.
The liver function panel evaluates hepatocyte integrity (ALT, AST), biliary function (GGT, ALP, bilirubin), and synthetic capacity (albumin, total protein). While a standard CMP includes ALT, AST, and ALP, a dedicated liver panel adds GGT and direct bilirubin — critical for distinguishing hepatocellular from cholestatic patterns. Combined with the FIB-4 score (calculated from age, AST, ALT, and platelets), this panel non-invasively stages liver fibrosis without imaging or biopsy.
Hepatocellular damage markers (ALT, AST), biliary/cholestatic markers (GGT, ALP, bilirubin), and liver synthetic function (albumin, total protein). The pattern of elevation — not just the absolute values — determines the clinical interpretation. ALT-predominant elevation suggests hepatocellular injury; ALP/GGT-predominant suggests biliary obstruction or cholestasis.
What's included.
- ALT (Alanine Aminotransferase) — normal: M: 7-56 / F: 7-45 U/L · Most specific liver enzyme — elevated = hepatocyte damage. Optimal: M <30, F <19
- AST (Aspartate Aminotransferase) — normal: 10-40 U/L · Less liver-specific (also in muscle, heart). AST:ALT >2:1 suggests alcoholic liver disease
- GGT (Gamma-Glutamyl Transferase) — normal: M: 8-61 / F: 5-36 U/L · Most sensitive biliary marker. Confirms hepatic ALP. Alcohol and metabolic syndrome sensitive
- ALP (Alkaline Phosphatase) — normal: 44-147 U/L · Biliary/bone origin — GGT distinguishes. Elevated in obstruction, pregnancy, bone disease
- Total Bilirubin — normal: 0.1-1.2 mg/dL · Haem breakdown product. Elevated = jaundice. Direct vs indirect fraction determines cause
- Albumin — normal: 3.5-5.5 g/dL · Liver synthetic function marker. Low = chronic liver disease, malnutrition, or inflammation
Preparation.
No fasting required.
When: Can be drawn at any time. Morning fasting draw preferred for consistency and if metabolic tests are ordered simultaneously.
- No fasting strictly required, but fasting improves consistency
- Avoid alcohol for 48-72 hours before testing for accurate GGT baseline
- Note all medications — many affect liver enzymes (statins, antibiotics, anticonvulsants)
- Avoid strenuous exercise 24 hours before (can elevate AST from muscle)
- Biotin supplements do not interfere with liver tests
When it's ordered.
- Elevated ALT or AST found on routine metabolic panel
- Suspected fatty liver disease (MASLD) — obesity, metabolic syndrome, diabetes
- Alcohol use assessment
- Jaundice (yellowing of skin or eyes)
- Right upper quadrant pain
- Monitoring hepatotoxic medications (statins, methotrexate, acetaminophen)
- Screening in high-risk populations (hepatitis B/C risk factors, family history)
- Pre-surgical assessment
Interpretation.
What normal means
Hepatocytes are intact, bile flow is unobstructed, and the liver is synthesising proteins normally. Note: a normal ALT does not exclude MASLD — up to 30% of fatty liver cases have normal ALT.
Abnormal patterns
ALT elevated (2-5x ULN) with AST:ALT <1 and normal GGT/ALP (Hepatocellular — non-alcoholic)
Possible causes
- MASLD / fatty liver disease (most common)
- Drug-induced liver injury (DILI)
- Viral hepatitis (B or C)
- Autoimmune hepatitis
- Celiac disease (cryptogenic elevation)
Next steps
- Calculate FIB-4 score for fibrosis risk
- Check hepatitis B/C serology
- Check autoimmune markers (ANA, anti-smooth muscle antibody) if <50 years
- Check tTG-IgA (celiac screen) if no other cause identified
- Abdominal ultrasound for steatosis
AST:ALT ratio >2:1 with elevated GGT (Hepatocellular — alcoholic pattern)
Possible causes
- Alcoholic liver disease
- Advanced fibrosis/cirrhosis (any cause)
Next steps
- Assess alcohol intake honestly
- FIB-4 score and consider FibroScan
- If advanced disease suspected: hepatology referral
ALP and GGT elevated with normal ALT/AST (Cholestatic pattern)
Possible causes
- Biliary obstruction (gallstones, stricture, tumour)
- Primary biliary cholangitis (PBC)
- Primary sclerosing cholangitis (PSC)
- Drug-induced cholestasis
- Infiltrative liver disease
Next steps
- Abdominal ultrasound (bile duct dilation?)
- If ultrasound normal: check AMA (anti-mitochondrial antibody for PBC)
- MRCP if obstruction suspected
- Gastroenterology/hepatology referral
Elevated ALP with normal GGT (Bone origin)
Possible causes
- Paget's disease
- Bone fracture healing
- Pregnancy (third trimester)
- Adolescent growth
- Vitamin D deficiency with secondary hyperparathyroidism
Next steps
- Not a liver problem — investigate bone pathology
- Check vitamin D, calcium, PTH if clinically indicated
Low albumin with elevated bilirubin (Liver synthetic failure)
Possible causes
- Cirrhosis (any aetiology)
- Decompensated liver disease
- Severe acute hepatitis
- Hepatocellular carcinoma
Next steps
- Urgent hepatology referral
- Check INR/PT (coagulation — another synthetic marker)
- Abdominal imaging
- Assess for portal hypertension signs (ascites, varices)
Cost & access.
Basic LFTs (ALT, AST, ALP, bilirubin, albumin) cost $20-60. Adding GGT adds $15-30. Most insurance covers with clinical indication. FIB-4 is calculated free from existing blood work.
FAQs.
What is the FIB-4 score and should I calculate mine?
FIB-4 = (Age x AST) / (Platelets x √ALT). It estimates liver fibrosis from routine blood work. Score <1.3 = low fibrosis risk (reassuring). 1.3-2.67 = indeterminate (consider FibroScan). >2.67 = high risk (hepatology referral). If your ALT is elevated, calculating FIB-4 is the most important next step.
My ALT is elevated but I don't drink — what could it be?
MASLD (fatty liver) is by far the most common cause. It affects 25-30% of adults and is driven by insulin resistance, obesity, and metabolic syndrome. Other non-alcoholic causes: medications (statins, antibiotics), viral hepatitis, autoimmune hepatitis, celiac disease, and haemochromatosis.
What does AST:ALT ratio tell you?
AST:ALT <1 is typical of non-alcoholic liver disease. AST:ALT >2:1 strongly suggests alcoholic liver disease or advanced cirrhosis. This ratio is one of the simplest and most clinically useful calculations in hepatology.
Can strenuous exercise affect my liver tests?
Yes — vigorous exercise can elevate AST (and to a lesser extent ALT) because AST is also present in skeletal and cardiac muscle. CK (creatine kinase) helps distinguish: if CK is also elevated, the AST rise is likely muscular, not hepatic. Avoid intense exercise 24 hours before testing.