A 23-year-old woman comes to the office due to sharp, right-sided chest pain, fatigue, and fever for the past week. The chest pain is worsened with deep breathing. She has had no associated expectoration or shortness of breath. For the past 6 months, the patient also has had intermittent joint pains, predominantly in the knees and hands. She is sexually active with one male partner and uses an intrauterine device for contraception. Temperature is 38.3 C (100.9 F), blood pressure is 120/70 mm Hg, pulse is 89/min, and respirations are 18/min. BMI is 24 kg/m². Examination shows mild erythema over the cheeks and a scratching sound over the right lower lung with breathing. Heart sounds are normal. There is no joint swelling. Which of the following tests is most useful in confirming the diagnosis?

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11ec160b_3a73_ed9d_9249_ffc839e058ad_MD0001_00 This young patient has pleuritis (chest pain worse with breathing, pleural rub), arthralgias, fever, and an erythematous rash on the cheeks. This presentation is concerning for systemic lupus erythematosus (SLE), a chronic inflammatory disease characterized by autoantibodies that bind self-antigens. Particular autoantibodies that are useful in the diagnosis of SLE include: Common laboratory abnormalities include low C3 and C4 levels (due to activation of complement) and elevated inflammatory markers (eg, C-reactive protein, erythrocyte sedimentation rate). Hematologic abnormalities can include anemia, leukopenia, and thrombocytopenia, which occur due to chronic inflammatory effects on bone marrow and autoimmune hemolysis. Renal involvement can result in elevated serum creatinine, proteinuria, hematuria, or red cell casts visible on urinalysis. (Choice B) Antibodies to streptolysin O indicate recent streptococcal infection and are useful in the diagnosis of certain immune sequelae (eg, glomerulonephritis, rheumatic fever). This patient has arthralgias, but no other major features of rheumatic fever (ie, carditis, subcutaneous nodules, erythema marginatum, Sydenham chorea). (Choice C) Acute cervicitis is a common cause of fever in young, sexually active women. Evaluation commonly includes nucleic acid amplification testing (NAAT) for organisms such as gonorrhea, chlamydia, and trichomoniasis. Although disseminated gonorrhea can cause arthralgias and rash, pleuritis is not typical. (Choice D) Rheumatoid factor is an IgM antibody directed against the Fc portion of human IgG. It is classically associated with rheumatoid arthritis, although it may also be seen in other autoimmune diseases (including SLE) and is nonspecific. Rheumatoid arthritis can cause arthralgias and lung involvement, but rash is unexpected and joint swelling is usually prominent. (Choice E) Nontreponemal serologic tests (eg, RPR, VDRL) are frequently used to screen for syphilis. Although secondary syphilis can manifest with synovitis and rash, it typically involves the palms and soles and pleural involvement is rare. Educational objective: Antinuclear antibodies are found in almost all patients with systemic lupus erythematosus but are also found in many other autoimmune disorders and have low specificity. Anti-double-stranded DNA antibodies and anti-Smith antibodies have lower sensitivity but higher specificity.

A 23-Year-Old Woman Comes to the Office Due to Sharp