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TABLE 2-18:

Tests for HCV (continued)
Test Cost Comment
Anti-HCV EIA $25 to $45 Indicates past or present HCV infection. Sensitivity of
the third generation tests is >99%. EIA lacks
specificity in low-prevalence populations –
supplemental assay required for confirmation. RIBA –
of little utility in HIV infected patients.
Qualitative HCV
RNA
(HCV RT-PCR)		 $160 to $200 RT-PCR technology to detect HCV RNA; may have
false-positives and negatives. Threshold for detection
is 50 IU/mL. Usual use is to confirm serology results.
Quantitative
HCV PCR or
bDNA		 $160 to $225 Determines concentration using RT-PCR or bDNA
technology. Less sensitive than qualitative RT-PCR.
Threshold of detection is 500 IU/mL; most patients
with chronic HCV infection have 105 to 107 c/mL.
HCV RNA level is not useful for determining
prognosis; it is used to monitor response to therapy.
Magnitude of HCV RNA level may predict response. It
has largely supplanted qualitative HCV RNA tests due
to adequate sensitivity and comparable cost.
Genotype $200 to $250 6 genotypes – genotype 1 predominates in U.S.
(70%) and shows poorest response to therapy. Better
response with genotypes 2 and 3.

treatment. Patients who are non-immune, should be vaccinated against HAV and HBV. Those who are considered candidates for HCV therapy should be evaluated as indicated on pg ___.

Toxoplasma Serology: Toxoplasma serology (anti-Toxoplasma IgG) is recom mended to assist in the differential diagnosis of complications involving the CNS, to identify candidates for toxoplasmosis prophylaxis (Ann Intern Med 1992;117:163), and to counsel patients on preventive measures if seronegative (See pg ___). The preferred method is an agglutination assay for IgG; IgM assays are not useful, and the Sabin- Feldman dye test is less accurate than the agglutination assay. Seroprevalence among adults in the United States is 10 to 30%, and the seroconversion rate is up to 1% per year. The sensitivity of the test is 95 to 97%. Most infec tions in AIDS patients represent relapse of latent infection, which is noted in 20 to 47% of those with CD4 counts <100 cells/mm3, positive Toxoplasma serology, and no prophylaxis (CID 1992;15:211; CID 2002;34: 103).

A negative Toxoplasma serology should be repeated after the CD4 cell count is ≤100 cells/mm3 if the patient does not take atovaquone or TMP-SMX prophlaxis for PCP (2008 NIH/CDC/IDSA Guidelines for the Prevention of Opportunistic Infections (http://aids.nih.gov) or whenever the diagnosis toxoplas mosis encephalitis is being considered when prior tests were negative or not done (See pg ____).
2007 © John G. Bartlett, M.D. All rights reserved.56

Chapter 2: Laboratory Tests

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