Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1403 page)

   Negative test results cannot exclude a diagnosis of TB.

   Results, especially negative responses, must be interpreted in the context of the patient’s state of immunocompetence.

   TSTs are preferred for the evaluation of children, especially those younger than 5 years of age.

   For patients with latent TB, IGRAs cannot be used to predict which patients will progress to reactivation disease.

   The use of IGRAs versus TSTs, as a first-line screening tool, must be determined on the basis of several factors, including cost, patient population served, likely compliance of patients with return visits, prior vaccination with BCG, and access to laboratory processing in a timely manner.

   The effect of recent live-virus vaccination on the performance of IGRAs has not been well studied. IGRAs may be performed prior to or on the same day as live-virus vaccination. Otherwise, the IGRA should be delayed for 4–6 weeks after vaccination.

   The effect of lymphopenia on IGRAs is unknown.

   The antigens used in IGRAs (ESAT-6 and CFP-10) are present in
Mycobacterium kansasii
,
M
.
szulgai
,
M
.
marinum
, and several other non–
M
.
tuberculosis
species. Infection with other mycobacterial species should be considered, and ruled out as appropriate, in patients with positive IGRA test results.

   
Common pitfalls:

   IGRAs (and TSTs) may be submitted for patients at very low risk for infection with
M
.
tuberculosis
.

   Delayed transport or improper specimen handling during transport may decrease the viability of lymphocytes and result in false-negative results.

Suggested Reading

Centers for Disease Control and Prevention. Updated guidelines for using interferon gamma release assays to detect mycobacterium tuberculosis infection—United States, 2010.
MMWR Morbid Mortal Wkly Rep.
2010;59(RR-5).

NEISSERIA GONORRHOEAE
, AMPLIFIED NUCLEIC ACID DETECTION

See: Sexually Transmitted Infections, Molecular Diagnosis (
Chlamydia trachomatis
,
Neisseria gonorrhoeae
,
Trichomonas vaginalis
)

OVA AND PARASITE EXAMINATION, STOOL

   Definition