For a patient with isolated elevated liver function tests, is a contrast‑enhanced abdominal CT appropriate as the initial imaging study?

CT Abdomen for Elevated Liver Function Tests

Ultrasound abdomen is the mandatory first-line imaging modality for isolated elevated liver function tests, not CT, because ultrasound detects steatosis, biliary pathology, and cirrhotic changes with 65-95% sensitivity while being radiation-free and cost-effective. 1

Initial Imaging Strategy

• Start with ultrasound abdomen as your primary screening tool for any patient presenting with elevated LFTs, as recommended by the American College of Radiology 1
• Ultrasound identifies the most common causes of elevated liver enzymes including moderate-to-severe hepatic steatosis (84.8% sensitivity, 93.6% specificity), biliary obstruction, focal liver lesions, and portal hypertension features 1, 2
• The "starry sky" appearance on ultrasound indicates acute hepatic parenchymal inflammation, with conspicuous portal triads against dark edematous liver parenchyma 3
• Contracted gallbladder with wall thickening (mean 5.2 mm) on ultrasound serves as a marker of hepatic dysfunction and can predict severe hepatitis 3

When CT Without Contrast Is Appropriate

• Order CT abdomen without IV contrast specifically to quantify moderate-to-severe hepatic steatosis when ultrasound findings are equivocal or you need precise measurement (100% specificity, 82% sensitivity) 1
• Liver attenuation <40 Hounsfield units on unenhanced CT indicates ≥30% steatosis, and liver-to-spleen attenuation difference >10 HU confirms moderate-to-severe disease 1
• CT without contrast is useful for detecting steatosis but has limited sensitivity for early or mild fatty infiltration 2

When CT With Contrast Is Appropriate

• Order CT abdomen with IV contrast urgently if you suspect ischemic liver injury (shock liver), acute hepatitis complications, or vascular pathology based on clinical presentation 1
• Contrast-enhanced CT identifies heterogeneous arterial enhancement, periportal hypoattenuation, perihepatic lymphadenopathy (>7 mm), and ascites that characterize acute hepatitis 3
• Ischemic hepatitis appears as hypoenhancement of liver parenchyma due to hypoperfusion, which can progress to liver failure with high mortality if not recognized urgently 3, 2
• Use CT with contrast to determine the etiology and site of biliary obstruction when ultrasound shows ductal dilatation, or to assess portal hypertension sequelae 1

Critical Pitfall to Avoid

• Never order CT abdomen with and without IV contrast for elevated LFTs because there is no benefit from adding unenhanced images in this clinical scenario, and it adds unnecessary radiation exposure and cost 3, 1
• Do not assume decreased liver attenuation on contrast CT equals benign steatosis, as ischemic liver injury is life-threatening and requires urgent recognition 1
• Do not skip ultrasound and proceed directly to CT, as this bypasses the most appropriate initial evaluation tool 1, 2

Algorithmic Approach Based on Clinical Context

For mild, asymptomatic LFT elevation:

• Order ultrasound abdomen first to screen for steatosis, biliary dilatation, cirrhosis, and masses 1
• If ultrasound shows hepatic steatosis, implement lifestyle modifications and calculate FIB-4 score to assess fibrosis risk 2
• If ultrasound shows biliary dilation, proceed to MRI abdomen with MRCP (90.7% accuracy for biliary obstruction) 2

For acute hepatocellular injury pattern (markedly elevated transaminases):

• Order ultrasound abdomen immediately as the portable first-line modality 3
• Add Duplex Doppler to assess vascular patency if ischemic insult is suspected 3
• Order CT abdomen with IV contrast if you suspect ischemic hepatitis, acute hepatitis complications, or need to identify vascular causes 3, 1

For cholestatic pattern (elevated alkaline phosphatase/GGT):

• Order ultrasound first to identify biliary obstruction 1
• If ultrasound shows ductal dilatation, proceed to CT with contrast or MRI with MRCP to determine obstruction etiology and site 1

When to Consider MRI Instead

• Order MRI abdomen without contrast (or with contrast + MRCP) when ultrasound and initial workup are inconclusive, as MRI detects ≥5% hepatic fat with 76.7-90% sensitivity and 87.1-91% specificity, far superior to CT for mild steatosis 1
• MRI with IV contrast assesses parenchymal inflammation showing increased T2 signal, decreased T1 signal, heterogeneous perfusion, and periportal edema as hyperintense signal 3
• MRI with MRCP is the most useful modality for identifying biliary obstruction etiology, especially with suspected intrahepatic cholestasis or persistent alkaline phosphatase elevation despite negative ultrasound 1