Examkin

Question

Difficulty: MediumOrdering Laboratory Tests

An independent 68-year-old male is evaluated in the outpatient clinic for progressive mid-to-lower back pain and generalized fatigue that has worsened over the past three months. He describes the pain as a deep, constant ache exacerbated by ambulation and poorly responsive to ibuprofen. He also reports a recent onset of constipation. His medical history is significant for essential hypertension treated with amlodipine. His temperature is 37.1°C (98.8°F), blood pressure is 134/84 mmHg, pulse is 82/min, and respiratory rate is 14/min. Physical examination reveals pale conjunctivae and point tenderness to palpation over the L3 and L4 spinous processes. Neurological examination of the lower extremities shows 5/5 strength, intact sensation to light touch and pinprick, and normal symmetric deep tendon reflexes. The prostate is smooth and mildly enlarged without nodules.

Initial laboratory studies show:

Hemoglobin: 10.1 g/dL
Mean corpuscular volume: 88 fL
Leukocyte count: 5,400/mm³
Platelet count: 210,000/mm³
Serum calcium: 11.4 mg/dL
Serum creatinine: 1.7 mg/dL
Blood urea nitrogen: 32 mg/dL
Total protein: 8.9 g/dL
Albumin: 3.8 g/dL

Which of the following is the most appropriate next step in the diagnostic workup?

  1. Serum protein electrophoresis and free light chain assayAnswer
  2. B
    Bone marrow aspiration and biopsy
  3. C
    Measurement of intact parathyroid hormone
  4. D
    Measurement of prostate-specific antigen
  5. E
    Magnetic resonance imaging of the lumbar spine

Answer

Serum protein electrophoresis and free light chain assay
The correct answer identifies the need to evaluate for a monoclonal gammopathy. This patient's presentation of hypercalcemia, renal failure, normocytic anemia, and bone pain constitutes the classic CRAB criteria for multiple myeloma. Furthermore, the laboratory results demonstrate a marked globulin gap (calculated as Total Protein−Albumin=8.9−3.8=5.1\text{Total Protein} - \text{Albumin} = 8.9 - 3.8 = 5.1 g/dL). A globulin gap greater than 4.04.0 g/dL is highly suggestive of an overproduction of monoclonal immunoglobulins. The most appropriate initial step to establish this diagnosis is ordering a serum protein electrophoresis (SPEP) with immunofixation and a serum free light chain assay.

Step-by-Step Solution

1
Analyze the clinical presentation.
The patient is an older male with new-onset bone pain, fatigue, and constipation.
Identifying the core symptom cluster guides the differential diagnosis toward systemic or neoplastic processes.
2
Interpret the basic laboratory panel.
The labs reveal hypercalcemia, renal insufficiency, normocytic anemia, and an elevated total protein with normal albumin.
These findings fulfill the classic CRAB criteria (Calcium elevation, Renal dysfunction, Anemia, Bone pain) indicative of multiple myeloma.
3
Calculate the globulin gap.
Total protein minus albumin is 8.9−3.8=5.18.9 - 3.8 = 5.1 g/dL (normal is < 4.0 g/dL).
A significantly elevated globulin gap strongly suggests the presence of excessive monoclonal proteins (paraproteinemia).
4
Determine the most appropriate next step.
Select non-invasive screening for monoclonal proteins.
Before pursuing invasive confirmatory procedures (like a bone marrow biopsy), initial laboratory confirmation of a monoclonal gammopathy must be obtained.

Key Concept

Patients presenting with bone pain, hypercalcemia, anemia, and a large globulin gap should undergo initial evaluation for multiple myeloma using serum protein electrophoresis (SPEP) and a free light chain assay.
Estimated Time:1m 30s
Rate this question

Topics

Ordering Laboratory Tests

More questions from this topic