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Difficulty: MediumOrdering Laboratory Tests

Evaluate the following distinct patient encounters. For each clinical presentation, select the most appropriate targeted laboratory testing panel to establish the diagnosis.

  • A 24-year-old male presents with a firm, painless ulcer on his glans penis and bilateral rubbery inguinal lymph nodes; he reports unprotected intercourse with a new partner 3 weeks ago.Treponemal-specific immunoassay followed by a non-treponemal test (e.g., rapid plasma reagin) for confirmation and titering.
  • A 32-year-old female returns from a vacation in Puerto Rico and develops a sudden high-grade fever, severe retro-orbital pain, diffuse myalgias, and a generalized maculopapular rash.Dengue virus NS1 antigen assay combined with specific IgM enzyme-linked immunosorbent assay (ELISA).
  • A 45-year-old male experiences a chronic, productive cough, drenching night sweats, and a 10-pound unintentional weight loss over four weeks; chest radiography reveals an apical cavitary lesion.Sputum acid-fast bacilli (AFB) smear, mycobacterial culture, and nucleic acid amplification testing (NAAT).
  • A 19-year-old college student complains of a 5-day history of extreme fatigue, severe sore throat with tonsillar exudates, and prominent posterior cervical lymphadenopathy; a rapid antigen detection test for Group A Streptococcus is negative.Heterophile antibody screening and Epstein-Barr virus (EBV) viral capsid antigen IgM.

Answer

Primary syphilis matches with Treponemal/Non-treponemal testing; Dengue fever matches with NS1 antigen and IgM ELISA; Active pulmonary tuberculosis matches with Sputum AFB, culture, and NAAT; Infectious mononucleosis matches with Heterophile antibody and EBV VCA IgM.
Each pairing links a highly specific clinical vignette to the standard-of-care initial diagnostic laboratory evaluation required to establish the diagnosis, matching the syndrome to the correct microbiological or serological assay.

Step-by-Step Solution

1
Analyze the clinical features and epidemiologic risks of the 24-year-old male with a painless penile ulcer.
Identify primary syphilis as the most likely diagnosis.
A painless, indurated ulcer (chancre) and regional lymphadenopathy are highly specific for Treponema pallidum infection.
2
Select the appropriate laboratory test for primary syphilis.
Match with Treponemal-specific immunoassay and non-treponemal test.
Modern syphilis screening utilizes a reverse sequence algorithm (treponemal test first) or traditional algorithm, both requiring both test types for confirmation.
3
Analyze the 32-year-old female returning from Puerto Rico with retro-orbital pain and myalgias.
Identify dengue fever.
Travel to an endemic area combined with high fever, retro-orbital headache, and severe muscle pain characterizes dengue.
4
Select the appropriate laboratory test for acute dengue fever.
Match with Dengue virus NS1 antigen and IgM ELISA.
During the acute phase (days 1-7), the NS1 antigen is highly detectable, while IgM appears slightly later but confirms acute infection.
5
Evaluate the 45-year-old male with chronic cough, night sweats, and a cavitary lesion.
Identify pulmonary tuberculosis.
The chronicity of symptoms combined with classic radiographic findings (apical cavitation) points to Mycobacterium tuberculosis.
6
Determine the diagnostic workup for suspected active tuberculosis.
Match with Sputum AFB smear, mycobacterial culture, and NAAT.
Three sputum samples are required for smear and culture to isolate the organism and determine susceptibility, with NAAT providing rapid confirmation.
7
Assess the 19-year-old student with severe pharyngitis, posterior cervical adenopathy, and a negative strep test.
Identify infectious mononucleosis.
Posterior cervical lymphadenopathy and pronounced fatigue, especially in a young adult with a negative strep test, strongly indicate EBV infection.
8
Select the lab test for infectious mononucleosis.
Match with Heterophile antibody screening and EBV VCA IgM.
The heterophile antibody test is a rapid, specific screen for EBV in symptomatic patients, while EBV VCA IgM confirms acute infection if the monospot is negative.

Key Concept

Selection of targeted diagnostic laboratory panels based on specific clinical infectious disease presentations and epidemiological risk factors.
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Topics

Ordering Laboratory Tests

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