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Difficulty: EasyOrdering Laboratory Tests

Match each classic clinical presentation with the most appropriate initial diagnostic laboratory test to order.

  • A 22-year-old college student with a 2-week history of severe fatigue, exudative pharyngitis, and posterior cervical lymphadenopathy.Heterophile antibody test
  • A 65-year-old man with acute onset of severe epigastric pain radiating to the back, nausea, and a history of heavy alcohol use.Serum lipase level
  • A 50-year-old asymptomatic man with an incidentally discovered serum calcium level of 11.2 mg/dL on a routine comprehensive metabolic panel.Serum intact parathyroid hormone (PTH) level
  • A 40-year-old recent immigrant with a 4-week history of productive cough, hemoptysis, night sweats, and unintentional weight loss.Sputum acid-fast bacilli (AFB) smear and culture

Answer

The presentations map to their respective primary diagnostic tests: Mononucleosis requires a Heterophile antibody test, Acute Pancreatitis requires a Serum lipase level, incidental hypercalcemia requires a Serum intact parathyroid hormone (PTH) level, and suspected Tuberculosis requires a Sputum AFB smear and culture.
Each clinical vignette provides classic pathognomonic signs and symptoms for a specific common disease, which dictates a straightforward, guideline-recommended initial diagnostic laboratory test to confirm the clinical suspicion.

Step-by-Step Solution

1
Analyze the clinical presentation of the 22-year-old patient with pharyngitis and lymphadenopathy.
Identify suspected infectious mononucleosis and select the heterophile antibody test.
The heterophile antibody test provides rapid diagnostic confirmation for the classic clinical syndrome of Epstein-Barr virus infection.
2
Evaluate the 65-year-old patient with severe epigastric pain and alcohol use.
Identify suspected acute pancreatitis and select serum lipase level.
Serum lipase rises quickly in acute pancreatitis and has higher sensitivity and specificity than amylase.
3
Assess the 50-year-old patient with isolated hypercalcemia.
Identify the need to determine the etiology of hypercalcemia and select serum intact parathyroid hormone (PTH) level.
Measuring intact PTH is the standard initial algorithm step to differentiate primary hyperparathyroidism from malignancy or other causes.
4
Review the presentation of the 40-year-old immigrant with a chronic cough and hemoptysis.
Identify suspected pulmonary tuberculosis and select sputum AFB smear and culture.
Detecting mycobacteria in sputum is essential for the diagnosis and public health management of active pulmonary tuberculosis.

Key Concept

Selecting the most appropriate initial diagnostic laboratory test based on classic pathognomonic clinical presentations.
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Ordering Laboratory Tests

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