Step 2 CK · Internal Medicine · Gastroenterology

Approach to Abnormal Liver Tests

Name: Approach to Abnormal Liver Tests
Creator: Veli Bakalov, MD

Name the pattern, and let it choose the next test

Gastroenterology·Hepatitis & Liver Injury·6 min read·9 high-yield points·Reviewed by Veli Bakalov, MD @HemeOncBuddy

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Name the pattern first: hepatocellular (ALT/AST), cholestatic (ALP ± bilirubin, with GGT confirming a hepatic source) or isolated hyperbilirubinemia; only INR and albumin measure synthetic function.
ALT/AST above 1000: ischemic hepatitis, acute viral hepatitis, acetaminophen, autoimmune hepatitis, acute Budd-Chiari, Wilson disease or a passed CBD stone—always send an acetaminophen level.
AST:ALT above 2:1 with AST under 300–500 suggests alcohol; an AST-predominant rise with a high CK suggests muscle.
Persistent mild elevation is most often MASLD; then check alcohol, drugs and supplements, HBV, HCV and iron studies, followed by autoimmune hepatitis, Wilson (under 40), alpha-1 antitrypsin, celiac, thyroid and CK.
A mild unconjugated bilirubin rise with fasting and a normal CBC, LDH and haptoglobin is Gilbert syndrome: reassure.
Isolated conjugated hyperbilirubinemia with normal enzymes is Dubin-Johnson or Rotor syndrome, both benign.
Cholestasis → RUQ ultrasound: dilated ducts → MRCP or EUS (ERCP for therapy); nondilated → drugs, AMA for PBC, MRCP for PSC, infiltrative disease, then biopsy.
A normal GGT with a high ALP means bone or third-trimester placenta, not liver.
INR ≥1.5 with encephalopathy after acute injury is acute liver failure; an INR that corrects with vitamin K reflects deficiency rather than failed synthesis.

Reading the liver panel

Injury versus function. The so-called liver function tests mostly measure injury. Aminotransferases leak from damaged hepatocytes, alkaline phosphatase (ALP) and GGT rise when bile flow is impaired, and bilirubin reflects uptake, conjugation and excretion. Only the INR (prothrombin time) and albumin reflect synthetic function. The misnomer cuts both ways: ALT can be in the thousands with preserved function, and a burned-out cirrhotic liver can have normal enzymes.

What each test tells you

Test	Reflects	Other sources and caveats
ALT	Hepatocyte injury (liver cytosol)	The most liver-specific enzyme
AST	Hepatocyte injury (cytosol and mitochondria)	Skeletal and cardiac muscle, red cells (hemolysis)
ALP	Cholestasis	Bone, placenta (third trimester), intestine
GGT	Cholestasis; confirms a hepatic ALP	Raised by alcohol and enzyme inducers such as phenytoin
Bilirubin	Uptake, conjugation, excretion	Unconjugated fraction rises with hemolysis and Gilbert syndrome
INR	Synthesis (factor VII half-life ~6 h)	Also prolonged by vitamin K deficiency and warfarin
Albumin	Synthesis (half-life ~3 weeks)	Low in malnutrition, nephrotic syndrome, inflammation

Name the pattern. Hepatocellular injury has ALT and AST out of proportion to ALP; cholestatic injury has ALP (with or without bilirubin) out of proportion to the aminotransferases; isolated hyperbilirubinemia has normal enzymes. The R ratio—(ALT ÷ ULN) ÷ (ALP ÷ ULN)—formalizes it: ≥5 hepatocellular, ≤2 cholestatic, 2–5 mixed. Each pattern has its own algorithm.

Synthetic failure. A prolonged INR that corrects after parenteral vitamin K reflects deficiency (cholestasis with fat malabsorption, malnutrition, antibiotics); failure to correct means impaired synthesis. Because albumin turns over slowly, it lags in acute injury, while the INR rises within a day. In acute liver injury, an INR ≥1.5 with any encephalopathy defines acute liver failure and warrants ICU care and early transplant-center referral. Falling aminotransferases with a rising bilirubin and INR signal massive necrosis, not recovery.

Hepatocellular pattern

Aminotransferases above 1000 U/L. Few conditions produce values this high:

Causes of ALT/AST above 1000 U/L

Cause	Clues	Key test
Ischemic hepatitis	Shock, heart failure, sepsis; LDH very high (ALT:LDH <1.5); falls by half within days	Clinical context, echocardiography
Acute viral hepatitis	Prodrome, exposure, travel; HSV in pregnancy or immunosuppression	IgM anti-HAV, HBsAg + IgM anti-HBc, HCV RNA, HEV IgM, HSV PCR
Acetaminophen	Overdose or chronic excess, especially with alcohol or fasting	Acetaminophen level (always)
Autoimmune hepatitis	Woman with other autoimmune disease; high IgG	ANA, anti-smooth muscle, IgG
Acute Budd-Chiari	Abdominal pain, ascites, hepatomegaly; hypercoagulable state	Doppler ultrasound
Wilson disease	Age <40, Coombs-negative hemolysis, very low ALP	Ceruloplasmin, urine copper
Passed CBD stone	Biliary pain; spike falls within 24–72 h as ALP and bilirubin rise	Ultrasound, MRCP

Ischemic hepatitis. After hypoperfusion from shock, heart failure or sepsis, AST and ALT jump into the thousands within 24–48 hours with a markedly raised LDH, then fall by about half within a few days once perfusion returns; bilirubin peaks later.

Acute hepatitis workup. Send an acetaminophen level whatever the history, viral serologies (IgM anti-HAV, HBsAg and IgM anti-HBc, anti-HCV with HCV RNA, HEV IgM when relevant, HSV PCR in pregnancy or immunosuppression), ANA, anti-smooth muscle antibody and IgG, a ceruloplasmin under age 40, and a Doppler ultrasound. Check the INR and mental status to catch liver failure early.

Alcohol signature. Alcohol-associated liver disease produces an AST:ALT ratio ≥2:1 with AST usually below 300–500 U/L: alcohol injures mitochondria, releasing mitochondrial AST, and deficiency of pyridoxal-5′-phosphate, the ALT cofactor, blunts the ALT rise. A raised GGT and macrocytosis support it. An AST in the thousands in a drinker signals a second process—ischemia, or acetaminophen toxicity, because alcohol induces CYP2E1 and depletes glutathione. An AST:ALT ratio above 1 also accompanies cirrhosis of any cause.

AST is not liver-specific. An AST-predominant rise with a high CK points to muscle—rhabdomyolysis, strenuous exercise, myositis, hypothyroidism—and hemolysis raises AST and LDH together.

Chronic mild aminotransferase elevation

MASLD first. Metabolic dysfunction–associated steatotic liver disease (formerly NAFLD) is the most common cause of persistent mild elevation, typically ALT greater than AST until cirrhosis, in patients with obesity, type 2 diabetes, dyslipidemia or hypertension; ultrasound shows an echogenic liver. Stage fibrosis with the FIB-4 score (below 1.3 = low risk; 1.3 or higher → elastography) and treat with weight loss—losing 7–10% of body weight improves steatohepatitis.

Confirm and take a historyRepeat the test; quantify alcohol; list medications and herbal or dietary supplements.
Common causesMASLD, HBV (HBsAg, anti-HBc, anti-HBs), HCV (antibody, then RNA), hemochromatosis (transferrin saturation, ferritin).
Less common causesAutoimmune hepatitis (ANA, anti-smooth muscle, IgG), Wilson disease if under 40 (ceruloplasmin), alpha-1 antitrypsin deficiency (level and phenotype).
Nonhepatic causesCeliac disease (tTG-IgA; enzymes normalize on a gluten-free diet), thyroid disease (TSH), muscle disease (CK).
Still unexplainedLiver biopsy if the elevation persists or fibrosis is suspected.

Isolated hyperbilirubinemia

Unconjugated. An isolated indirect bilirubin rise means excess production (hemolysis, ineffective erythropoiesis, hematoma resorption) or impaired conjugation. Gilbert syndrome—reduced UGT1A1 activity, present in roughly 5–10% of people—causes a mild rise, usually below 3–4 mg/dL, with fasting, illness, stress or exertion. CBC, reticulocytes, LDH, haptoglobin and liver enzymes are normal, and no further testing or treatment is needed. Hemolysis instead brings anemia, reticulocytosis, a raised LDH and a low haptoglobin.

Conjugated with normal enzymes. Dubin-Johnson and Rotor syndromes impair handling of conjugated bilirubin but are benign and untreated. Conjugated bilirubin is water-soluble, so it appears in urine and darkens it; unconjugated bilirubin does not. A conjugated rise with abnormal enzymes is evaluated as cholestasis.

Inherited and hemolytic hyperbilirubinemias

Condition	Bilirubin	Defect	Key features
Gilbert	Unconjugated	↓UGT1A1 activity	Rises with fasting or illness; benign
Crigler-Najjar type I	Unconjugated	Absent UGT1A1	Neonatal kernicterus; phototherapy, transplant
Crigler-Najjar type II	Unconjugated	Severely ↓UGT1A1	Responds to phenobarbital
Hemolysis	Unconjugated	Excess heme breakdown	Anemia, reticulocytosis, ↑LDH, ↓haptoglobin
Dubin-Johnson	Conjugated	MRP2 canalicular excretion	Black liver; unmasked by oral contraceptives or pregnancy; benign
Rotor	Conjugated	OATP1B1/1B3 hepatic uptake	Normal-appearing liver; benign

Cholestatic pattern

Confirm the source. A raised GGT or 5′-nucleotidase confirms that an elevated ALP is hepatic. A normal GGT points to bone (Paget disease, osteoblastic metastases, healing fractures, adolescent growth, hyperparathyroidism) or to normal third-trimester pregnancy. GGT alone is nonspecific and should be used only for this confirmation.

RUQ ultrasoundThe first test for hepatic cholestasis: are the bile ducts dilated?
Dilated ductsExtrahepatic obstruction (choledocholithiasis, pancreatic or ampullary cancer, cholangiocarcinoma, stricture) → MRCP or EUS to define it; ERCP when stone extraction, stenting or brushings are needed.
Nondilated ductsReview drugs; send AMA for PBC; MRCP for PSC; consider infiltrative disease, sepsis and TPN.
Still unexplainedAMA-negative with a normal MRCP → liver biopsy.

Intrahepatic causes. Drug-induced cholestasis (amoxicillin-clavulanate, anabolic steroids, estrogens, chlorpromazine, TMP-SMX) is common and often delayed. Primary biliary cholangitis typically affects middle-aged women with fatigue and pruritus and is diagnosed by a positive antimitochondrial antibody with a raised ALP, without biopsy. Primary sclerosing cholangitis, usually in younger men with ulcerative colitis, shows multifocal strictures and beading on MRCP. Sepsis, total parenteral nutrition and congestive hepatopathy also cause cholestasis.

A markedly raised ALP with near-normal bilirubin and aminotransferases suggests infiltration—granulomas (sarcoidosis, tuberculosis, fungi), lymphoma, amyloidosis or metastases—diagnosed by imaging and liver biopsy.