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Difficulty: MediumOrdering Laboratory Tests

A 4141-year-old woman comes to the primary care clinic for evaluation of joint pain and stiffness that began gradually over the past 33 months. She reports that the pain primarily affects her wrists and fingers on both hands. The stiffness is most pronounced upon awakening and typically takes about 22 hours to improve. She feels generally fatigued but denies fevers, weight loss, or skin rashes. Her vital signs are within normal limits. Physical examination demonstrates boggy swelling, warmth, and tenderness of the second and third metacarpophalangeal and proximal interphalangeal joints bilaterally. There is no erythema or joint deformity. A routine complete blood count obtained last week for a wellness visit showed a hemoglobin level of 11.2 g/dL11.2 \text{ g/dL} and a mean corpuscular volume of 88 fL88 \text{ fL}. Which of the following is the most appropriate next step in the diagnostic workup?

  1. A
    Magnetic resonance imaging of the hands and wrists
  2. B
    Measurement of serum ferritin and transferrin saturation
  3. Serologic testing for rheumatoid factor and anti-cyclic citrullinated peptide antibodiesAnswer
  4. D
    Arthrocentesis of an affected metacarpophalangeal joint
  5. E
    Measurement of serum uric acid concentration

Answer

Serologic testing for rheumatoid factor and anti-cyclic citrullinated peptide antibodies
The patient presents with classic signs and symptoms of rheumatoid arthritis, including insidious onset of symmetric polyarthritis involving the metacarpophalangeal and proximal interphalangeal joints, prolonged morning stiffness lasting more than one hour, and systemic symptoms like fatigue. The most appropriate initial diagnostic step is serologic testing for rheumatoid factor and anti-cyclic citrullinated peptide antibodies. Anti-cyclic citrullinated peptide antibodies are highly specific for rheumatoid arthritis and help confirm the diagnosis, while rheumatoid factor is sensitive but less specific.

Step-by-Step Solution

1
Identify the primary clinical syndrome from the patient's history and physical examination.
The patient has a chronic (greater than 6 weeks), symmetric inflammatory polyarthritis affecting the small joints of the hands, with prolonged morning stiffness.
Recognizing this classic pattern strongly suggests rheumatoid arthritis as the primary diagnosis.
2
Determine the most appropriate initial diagnostic modality.
Targeted laboratory serology is the standard next step to support the clinical diagnosis of rheumatoid arthritis.
Serologic testing provides specific diagnostic and prognostic information without the need for invasive procedures or expensive advanced imaging.
3
Select the specific laboratory tests indicated for this presentation.
Testing for rheumatoid factor and anti-cyclic citrullinated peptide antibodies is indicated.
These biomarkers are highly characteristic of rheumatoid arthritis and are essential components of the diagnostic criteria.

Key Concept

The initial diagnostic workup for a patient presenting with classic symptoms of rheumatoid arthritis (symmetric polyarthritis, prolonged morning stiffness) includes serologic testing for rheumatoid factor (RF) and anti-cyclic citrullinated peptide (anti-CCP) antibodies.
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Ordering Laboratory Tests

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