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Difficulty: MediumOrdering Laboratory Tests

A 28-year-old woman, gravida 3, para 1, abortus 1, comes to the clinic for a routine prenatal visit at 11 weeks gestation. She has a healthy 3-year-old child and a history of a spontaneous abortion at 10 weeks gestation last year. Over the past 6 months, she has noticed that her fingers frequently turn pale, then blue, and finally red when exposed to cold weather. She also reports intermittent aching in her wrists and knees, but denies any morning stiffness lasting longer than a few minutes. Vital signs are temperature 37.0°C (98.6°F), blood pressure 118/76 mm Hg, pulse 82/min, and respirations 14/min. Physical examination shows no joint swelling, warmth, or erythema. There are no skin rashes, oral ulcers, or alopecia.

Initial laboratory results are as follows:

Hemoglobin: 11.2 g/dL
Leukocyte count: 4,500/mm³
Platelet count: 115,000/mm³
Urinalysis: 1+ protein, no red blood cells or casts

Which of the following is the most appropriate next step in laboratory evaluation?

  1. Antinuclear antibody and antiphospholipid antibody panelAnswer
  2. B
    Anti-double-stranded DNA and anti-Smith antibodies
  3. C
    24-hour urine protein quantitation
  4. D
    Direct antiglobulin test
  5. E
    Serum complement levels

Answer

The most appropriate next step is to order an antinuclear antibody and antiphospholipid antibody panel to screen for Systemic Lupus Erythematosus and Antiphospholipid Syndrome.
The correct answer identifies the need for highly sensitive initial screening tests. The patient's constellation of symptoms (Raynaud phenomenon, arthralgias, history of miscarriage, thrombocytopenia, and proteinuria) raises high clinical suspicion for Systemic Lupus Erythematosus (SLE) and secondary Antiphospholipid Syndrome (APS). The most appropriate initial laboratory step is screening with an Antinuclear Antibody (ANA) test, which has excellent sensitivity for SLE. Concurrently, screening for APS with an antiphospholipid antibody panel (lupus anticoagulant, anticardiolipin antibodies, and anti-beta-2 glycoprotein I antibodies) is indicated due to her history of spontaneous abortion and current thrombocytopenia.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and obstetric history.
The patient exhibits Raynaud phenomenon, arthralgias, a history of a first-trimester spontaneous abortion, mild thrombocytopenia, and proteinuria.
Identifying the syndromic constellation of signs and symptoms is necessary to formulate a prioritized differential diagnosis.
2
Formulate the most likely differential diagnosis.
The combination of findings is highly suggestive of an undiagnosed systemic autoimmune condition, specifically Systemic Lupus Erythematosus (SLE) and secondary Antiphospholipid Syndrome (APS).
SLE frequently presents in women of childbearing age with joint pain, Raynaud's, cytopenias, and renal involvement, while APS is strongly associated with recurrent or unexplained pregnancy loss.
3
Determine the most appropriate initial laboratory evaluation based on the suspected diagnosis.
The initial evaluation requires highly sensitive screening tests: the Antinuclear Antibody (ANA) test for SLE and an antiphospholipid antibody panel for APS.
Highly sensitive tests should be ordered first to efficiently rule out or screen for the condition. Specific confirmatory tests should only follow a positive screening test.

Key Concept

The initial laboratory evaluation of suspected Systemic Lupus Erythematosus (SLE) requires highly sensitive screening with an Antinuclear Antibody (ANA) test, followed by specific confirmatory testing if positive. Co-evaluation for Antiphospholipid Syndrome (APS) is indicated in patients with a history of pregnancy loss and cytopenias.
Estimated Time:1m 15s
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Ordering Laboratory Tests

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