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Question

Difficulty: MediumOrdering Laboratory Tests

For each of the following specific patient encounters, select the most appropriate targeted laboratory investigation required to establish the diagnosis.

  • A 30-year-old woman presents with episodic pounding headaches, excessive sweating, and unexplained tachycardia. During an episode in the clinic, her blood pressure is recorded at 185/115 mm Hg.Plasma free fractionated metanephrines
  • A 45-year-old woman reports a 6-month history of a 'sandy' feeling in her eyes, difficulty swallowing dry foods without liquids, and noticeable swelling in her bilateral cheeks.Anti-Ro/SSA and anti-La/SSB antibodies
  • A 25-year-old woman is evaluated for a history of heavy menstrual periods, recurrent epistaxis, and prolonged bleeding following a dental extraction. Her complete blood count shows a normal platelet count.von Willebrand factor antigen and ristocetin cofactor assay
  • A 55-year-old man presents with progressive fatigue, diffuse darkening of the skin, and newly diagnosed diabetes mellitus. He mentions a family history of unspecified liver cirrhosis.Serum iron panel and HFE genetic testing

Answer

The clinical vignettes describe characteristic presentations of pheochromocytoma, Sjögren syndrome, von Willebrand disease, and hereditary hemochromatosis. Each requires a highly specific initial laboratory evaluation to accurately confirm the suspected diagnosis.
Each clinical scenario contains distinct pathognomonic features that necessitate a targeted laboratory evaluation. Pheochromocytoma is efficiently screened via plasma free metanephrines due to continuous or episodic catecholamine release. Sjögren syndrome requires specific autoantibody screening (anti-Ro/La) to confirm autoimmune exocrinopathy. von Willebrand disease is confirmed by identifying deficient or dysfunctional vWF. Hereditary hemochromatosis is diagnosed by demonstrating iron overload followed by HFE genetic confirmation.

Step-by-Step Solution

1
Analyze the presenting clinical triad or symptom cluster for each patient to formulate the most likely suspected diagnosis.
Vignette 1 represents pheochromocytoma; Vignette 2 represents Sjögren syndrome; Vignette 3 represents von Willebrand disease; Vignette 4 represents hereditary hemochromatosis.
Recognizing pattern-based clinical presentations narrows down the broad differential diagnosis efficiently.
2
Determine the gold-standard initial targeted laboratory test or panel that is most appropriate to confirm or strongly support the primary suspected diagnosis for each scenario.
Pheochromocytoma requires plasma metanephrines; Sjögren syndrome requires anti-Ro/La antibodies; von Willebrand disease requires vWF assays; Hemochromatosis requires an iron panel and genetic testing.
Selecting the most sensitive and specific initial test optimizes diagnostic accuracy, limits unnecessary testing, and adheres to evidence-based clinical guidelines.
3
Map the specific laboratory investigations to the corresponding patient scenarios.
All four clinical vignettes are correctly aligned with their definitive diagnostic laboratory workups.
Completes the clinical reasoning process from presentation recognition to actionable diagnostic ordering.

Key Concept

Selecting the most appropriate and specific initial diagnostic laboratory test based on classic symptom triads and suspected underlying pathophysiology.
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Topics

Ordering Laboratory Tests

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