Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1329 page)

   Interpretation

   Reactivity scores: Specimen reactions with protein bands are first scored in terms of relative reaction intensity versus a cutoff control or minimally positive (“+”) band reaction intensity by a positive control specimen.

   
Test interpretation (IgM class reactivities)

   
Positive:
Reactivity scores of “+” or greater for at least two of three clinically significant proteins at the early stage of the disease (2–3 weeks after infection): 41, 39, 23 kDa

   
Negative:
Absence of any band reactivity on the test strip or reactivity for only one of the three clinically significant proteins

   
Test interpretation (IgG class reactivities)

   
Positive:
Reactivity scores of “+” or greater for at least 5 of 10 clinically significant proteins at the later stages of the disease (weeks to months after infection): 93, 66, 58, 45, 41, 39, 30, 28, 23, 18 kDa

   
Negative:
Absence of any band reactivity on the test strip or reactivity for <5 of the 10 clinically significant proteins

   Limitations

   Minimum specimen volume is 40 μL (20 μL each for the IgM and IgG tests).

   Like any second-tier test, the positive predictive value for a western blot assay is a function of the a priori likelihood of the disease by clinical and epidemiologic criteria, whereas the negative predictive value is not as well defined because of the variability of the immune response among infected individuals. Cross-reactive diseases are most frequently evidenced by reactivity to the 41-kDa flagellar protein and at much lower frequency to the 66-kDa heat shock protein. Specimens from patients diagnosed with
Ehrlichia
or
Babesia
infections can show other
Borrelia
-specific bands.

Suggested Reading

Branda JA, Aguero-Rosenfeld ME, Ferraro MJ, et al. 2-tiered antibody testing for early and late Lyme disease using only an immunoglobulin G blot with the addition of a VisE band as the second-tier test. Clin Infect Dis. 2010;50:20–26.

BRONCHIAL CULTURE (BAL OR BRUSH), QUANTITATIVE

   Definition