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Question

Difficulty: Very hardOrdering Laboratory Tests

Match each patient's complex clinical presentation with the most appropriate targeted laboratory testing panel or specific initial diagnostic test to order to establish the diagnosis.

  • A 34-year-old man with recurrent severe abdominal pain lacking peritoneal signs, accompanied by new-onset proximal muscle weakness, decreased deep tendon reflexes, and dark urine during the episodes. A recent abdominal CT scan was unremarkable.Measurement of spot urine porphobilinogen and delta-aminolevulinic acid
  • A 45-year-old woman with a history of Hashimoto thyroiditis presenting with progressive fatigue, diffuse pruritus, xanthelasma, hepatomegaly, and a markedly elevated alkaline phosphatase level with a normal right upper quadrant ultrasound.Serum testing for anti-mitochondrial antibodies
  • A 28-year-old man presenting with acute-onset hemoptysis, severe fatigue, bilateral diffuse alveolar infiltrates on chest radiography, and a urinalysis demonstrating 3+ hematuria with red blood cell casts.Serum testing for anti-glomerular basement membrane antibodies
  • A 52-year-old woman with chronic hepatitis C virus infection presenting with palpable purpura on the lower extremities, arthralgias, a positive rheumatoid factor, and an isolated markedly depressed serum complement C4 level.Measurement of serum cryoglobulin levels

Answer

The correct matches align each specific clinical syndrome with its definitive diagnostic laboratory test: Acute intermittent porphyria requires urine porphobilinogen and delta-aminolevulinic acid; Primary biliary cholangitis requires anti-mitochondrial antibodies; Goodpasture disease requires anti-glomerular basement membrane antibodies; and Mixed cryoglobulinemia requires serum cryoglobulin levels.
Each patient presentation corresponds to a distinct multisystem disease requiring a specific, targeted laboratory test to establish the diagnosis. The pairing relies on recognizing the pathognomonic clinical features and standard-of-care initial testing guidelines for each condition.

Step-by-Step Solution

1
Analyze the first clinical vignette to identify the underlying disease process.
The combination of recurrent neurovisceral symptoms (abdominal pain, neuropathy) and dark urine in a young adult strongly suggests acute intermittent porphyria.
Recognizing the clinical syndrome is prerequisite to ordering the specific confirmatory biochemical test.
2
Select the appropriate targeted test for acute intermittent porphyria.
Measurement of spot urine porphobilinogen and delta-aminolevulinic acid is selected.
These metabolites are elevated during acute porphyric attacks due to porphobilinogen deaminase deficiency.
3
Evaluate the second vignette featuring a woman with Hashimoto thyroiditis, pruritus, hepatomegaly, and elevated alkaline phosphatase.
This presentation is characteristic of primary biliary cholangitis, for which serum anti-mitochondrial antibodies are the diagnostic hallmark.
Anti-mitochondrial antibodies are highly sensitive and specific for primary biliary cholangitis.
4
Assess the third vignette describing a young man with hemoptysis, red blood cell casts, and bilateral alveolar infiltrates.
This pulmonary-renal syndrome points to Goodpasture disease, diagnosed by detecting serum anti-glomerular basement membrane antibodies.
Anti-glomerular basement membrane antibodies confirm the etiology of the rapidly progressive glomerulonephritis and alveolar hemorrhage.
5
Analyze the fourth vignette involving a patient with chronic hepatitis C, palpable purpura, and isolated low C4.
This classic triad indicates mixed cryoglobulinemia, which is confirmed by ordering measurement of serum cryoglobulin levels.
Hepatitis C is the most common cause of mixed cryoglobulinemia, characterized by immune complex deposition consuming C4.

Key Concept

Targeted laboratory test ordering for complex multisystem diseases based on highly specific pattern recognition of clinical syndromes.
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Ordering Laboratory Tests

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