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Difficulty: MediumOrdering Laboratory Tests

Review the following patient encounters. Which targeted laboratory evaluation is the most appropriate next step for each clinical presentation? Match each patient's scenario to the correct diagnostic test.

  • A 54-year-old man presents with persistent hypertension despite adherence to amlodipine, lisinopril, and chlorthalidone. A routine metabolic panel reveals a serum potassium level of 2.9 mEq/L.Plasma aldosterone concentration to plasma renin activity ratio
  • A 62-year-old woman reports a 4-month history of severe mid-back pain, worsening fatigue, and new-onset constipation. Laboratory evaluation shows a serum calcium of 11.5 mg/dL and creatinine of 1.8 mg/dL.Serum protein electrophoresis and serum free light chains
  • A 41-year-old woman complains of severe morning stiffness in her hands lasting over an hour and bilateral swelling of the metacarpophalangeal joints for the past 8 weeks.Rheumatoid factor and anti-cyclic citrullinated peptide antibodies
  • A 35-year-old man presents with acute-onset right-sided facial droop and mild headache. He recently returned from a camping trip in Connecticut but recalls no tick bites or rashes.Borrelia burgdorferi enzyme immunoassay with reflex immunoblot

Answer

The correct matches align the suspected clinical syndrome with its definitive initial screening test: the hypertensive hypokalemic man requires an aldosterone-to-renin ratio; the hypercalcemic woman with back pain needs serum protein electrophoresis and free light chains; the woman with symmetric small-joint polyarthritis requires rheumatoid factor and anti-CCP testing; and the man with isolated facial palsy after camping requires Borrelia burgdorferi serologies.
Each clinical presentation provides classic syndromic features that indicate a specific targeted laboratory evaluation. Resistant hypertension with hypokalemia necessitates biochemical screening for primary hyperaldosteronism. The CRAB criteria (hyperCalcemia, Renal insufficiency, Anemia, Bone lesions) strongly suggest multiple myeloma. Symmetric polyarthritis with prolonged morning stiffness indicates rheumatoid arthritis. Isolated facial nerve palsy with exposure to tick-endemic geographic areas points toward early disseminated Lyme disease.

Step-by-Step Solution

1
Analyze the 54-year-old man's presentation.
Identify primary hyperaldosteronism as the suspected diagnosis.
Resistant hypertension plus spontaneous hypokalemia is the classic presentation of primary hyperaldosteronism, requiring an aldosterone-to-renin ratio.
2
Analyze the 62-year-old woman's presentation.
Identify multiple myeloma as the suspected diagnosis.
The triad of hypercalcemia, renal failure, and bone pain in this demographic is characteristic of multiple myeloma, requiring protein electrophoresis and free light chain evaluation.
3
Analyze the 41-year-old woman's presentation.
Identify rheumatoid arthritis as the suspected diagnosis.
Bilateral metacarpophalangeal joint swelling with prolonged morning stiffness strongly suggests rheumatoid arthritis, indicating the need for RF and anti-CCP antibodies.
4
Analyze the 35-year-old man's presentation.
Identify early disseminated Lyme disease as the suspected diagnosis.
Bell's palsy in a patient with a history of travel to an endemic area is highly suspicious for Lyme disease, requiring two-tier serologic testing.

Key Concept

Matching patient presentations and pre-test disease probability to evidence-based diagnostic laboratory investigations.
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Topics

Ordering Laboratory Tests

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