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Difficulty: MediumOrdering Laboratory Tests

An otherwise healthy 47-year-old woman comes to the clinic because of severe, generalized pruritus for the past 4 months. She states the itching is most prominent on her palms and soles and worsens at night, significantly disrupting her sleep. She also reports progressive, debilitating fatigue. She takes no medications and does not consume alcohol. Her temperature is 37.1°C (98.8°F), blood pressure is 118/76 mm Hg, and pulse is 72/min. Physical examination shows multiple excoriations over the extremities and mild scleral icterus. There are no spider angiomas or palmar erythema. Abdominal examination reveals a smooth, non-tender liver edge palpable 2 cm below the right costal margin.

Laboratory studies are obtained:

Laboratory TestResultReference Range
Total bilirubin1.9 mg/dL0.1–1.2 mg/dL
Direct bilirubin1.4 mg/dL0.0–0.3 mg/dL
Alkaline phosphatase510 U/L30–120 U/L
Aspartate aminotransferase (AST)48 U/L8–40 U/L
Alanine aminotransferase (ALT)55 U/L7–56 U/L

A right upper quadrant ultrasound shows a normal-appearing liver and gallbladder without intrahepatic or extrahepatic biliary ductal dilation. Which of the following is the most appropriate next step in laboratory evaluation?

  1. Anti-mitochondrial antibody titerAnswer
  2. B
    Anti-smooth muscle antibody titer
  3. C
    Hepatitis C virus RNA polymerase chain reaction
  4. D
    Hereditary hemochromatosis gene (HFE) mutation analysis
  5. E
    Serum ceruloplasmin level

Answer

Anti-mitochondrial antibody titer
The correct next step is obtaining an anti-mitochondrial antibody titer. This patient's presentation of severe pruritus, fatigue, hepatomegaly, and a markedly elevated alkaline phosphatase out of proportion to AST and ALT indicates an intrahepatic cholestatic process. Furthermore, the normal ultrasound rules out extrahepatic obstruction (such as choledocholithiasis). This clinical and laboratory profile in a middle-aged woman is highly suspicious for primary biliary cholangitis (PBC). The anti-mitochondrial antibody (AMA) is the hallmark serologic marker for PBC and is found in up to 95% of patients with the disease, making it the most appropriate diagnostic test to order next.

Step-by-Step Solution

1
Analyze the patient's symptoms and physical examination findings.
A middle-aged woman presents with insidious onset of severe pruritus (especially on palms and soles), fatigue, hepatomegaly, and excoriations.
Identifying the demographic and primary symptom complex helps narrow the differential diagnosis for hepatobiliary diseases.
2
Interpret the laboratory and imaging results.
The labs reveal a profound elevation in alkaline phosphatase with minimal transaminase elevations (a cholestatic pattern), conjugated hyperbilirubinemia, and an ultrasound showing no biliary dilation.
Categorizing the liver injury as cholestatic rather than hepatocellular directs the diagnostic pathway. A normal ultrasound rules out extrahepatic biliary obstruction (e.g., gallstones, tumors).
3
Determine the most appropriate confirmatory laboratory test for the suspected condition.
The clinical picture strongly suggests primary biliary cholangitis (PBC). The anti-mitochondrial antibody (AMA) titer is highly sensitive and specific for PBC.
Choosing the correct autoantibody is required to definitively diagnose the underlying autoimmune destruction of intrahepatic bile ducts.

Key Concept

The initial evaluation of a cholestatic liver injury pattern (isolated elevated alkaline phosphatase) with a negative right upper quadrant ultrasound in a middle-aged woman should include testing for primary biliary cholangitis using the anti-mitochondrial antibody (AMA) assay.
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Ordering Laboratory Tests

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