A signal-to-cutoff ratio in the Abbott architect HIV Ag/Ab Combo assay that predicts subsequent confirmation of HIV-1 infection in a low-prevalence setting.

A rapid diagnosis is considered important in HIV care. In 138,911 testing episodes with the Abbott Architect HIV Ag/Ab Combo assay (3,705 reactive samples), a signal-to-cutoff ratio of >151.17 had a positive predictive value of 100% and a sensitivity of 67.4% for the detection of subsequently confirmed HIV infection. We suggest that results higher than this signal-to-cutoff ratio threshold may be reported to clinicians before the completion of confirmatory testing.

Prolonged second diagnostic window for human immunodeficiency virus type 1 in a fourth-generation immunoassay: are alternative testing strategies required?

Diagnosis of acute HIV is done by patient history and examination and testing of RNA, proviral DNA, and serology using fourth-generation antigen/antibody detection assays. We describe an HIV-1 primary infection with a second diagnostic window of 18 to 34 days on a fourth-generation immunoassay, which would have been missed using some current algorithms. Caution must be exercised when fourth-generation HIV-1 immunoassays are interpreted in isolation, and additional testing should be considered depending on patient risk assessment.

Infectious disease screening of blood specimens collected post-mortem provides comparable results to pre-mortem specimens.

Serology assays for standard screening are optimised for use with sera collected from living adults and children. Because of potential changes in the vascular compartments after death, methods used for screening sera from cadaveric organ donors need to be validated before testing these specimens. Serum was separated from blood collected from cadaveric donors within 24 h of death and biochemical parameters measured to detect dilution of protein and haemolysis. In order to demonstrate if any inhibitors that might interfere with the assays were present, pre and post-mortem specimens were spiked with aliquots of human immunodeficiency virus (HIV), hepatitis C virus (HCV), hepatitis B virus (HBV), human T-cell Lymphotropic Virus (HTLV) and T. pallidum-positive sera. Comparison of serum from living subjects with serum obtained post-mortem showed that while the concentration of total protein decreased, concentrations of albumin, immunoglobulin G (IgG) and immunoglobulin M (IgM) remained unchanged. The degree of haemolysis, as measured by free haemoglobin, was within the limits accepted for the Architect analyser. Spiking of pre- and post-mortem specimens with aliquots of HIV, HCV, HBV, HTLV and T. pallidum-positive sera showed no statistical difference in the signal between pre-mortem and post-mortem results when tested on the Abbott Architect analyser. Positive results were obtained in each of a further nine subjects who had tested positive for HIV (n=1), HCV (n=8), HBV (n=1) on pre-mortem serological testing. These findings suggest that the sensitivity of the Abbott Architect serological screening tests is not significantly affected in specimens collected within 24 h of the cessation of life.

Enhanced serological diagnosis of invasive meningococcal disease by determining anti-group C capsule IgM antibody by enzyme immunoassay.

AIMS: To describe the development and evaluation of a diagnostic enzyme immunoassay (EIA) for IgM antibody to serogroup C capsular polysaccharide of Neisseria meningitidis (CCPS). METHODS: Purified CCPS was used as the antigen. The optical densities (OD) that determined the cut-off values for the assay were derived using sera from blood bank donors, and the accuracy was evaluated with sera from patients with culture-confirmed serogroup C and non-serogroup C invasive meningococcal disease (IMD), other infectious diseases, culture-confirmed pharyngeal carriage of N. meningitidis and immunoproliferative disorders. RESULTS: In sera collected between days 5 and 20 following positive culture, the assay had a sensitivity of 92%. The two negative sera were from a single patient but showed a significant rise in OD. The sensitivity declined to 80% on days 21-40 then to 75% on days 41-70. No positive reactions were detected in five samples collected after 71 days. The specificity of the assay was at least 97%. CONCLUSIONS: An EIA for IgM antibody to CCPS was evaluated for local conditions and had acceptable sensitivity and specificity. Use of the assay, based on a single blood sample, provided clinically and epidemiologically relevant information for individual and public health management of IMD.

Measurement of EBV-IgG anti-VCA avidity aids the early and reliable diagnosis of primary EBV infection.

Current serological methods for the diagnosis of Epstein-Barr virus (EBV) infection still differentiate poorly between primary infection and reactivation. This is particularly true when IgG and IgM antibodies are present simultaneously and only a single serum sample is provided for analysis. The demonstration of the IgG avidity state has the potential to distinguish recent from past or reactivated infection. An analysis of the kinetics of avidity maturation of anti-VCA antibodies in primary EBV infection was undertaken with longitudinally collected sets of sera from 28 well-characterised EBV cases and in sera from 35 cases with previous EBV infection and recent primary infection due to HIV, CMV, or hepatitis A. Antibodies directed against the viral capsid antigen (VCA) and Epstein-Barr nuclear antigen (EBNA-1) were sought, using a commercial enzyme immunoassay (EIA). In parallel with standard IgG anti-VCA detection, serum was incubated with 8 M urea to disrupt low-avidity complexes to allow calculation of the percentage avidity. In cases with primary EBV infection, the mean avidity rose from 54% at 6 weeks to 82% by 28 weeks after the onset of symptoms, but remained lower than that of the control sera (96%). The addition of the avidity measurement improved the sensitivity of IgG and IgM anti-VCA testing in diagnosis of primary EBV infection from 93% to 100%. The specificity of IgM anti-VCA testing alone was poor, with 14 of 35 cases (49%) demonstrating false-positive results, but it improved to 97% by the demonstration of high-avidity IgG anti-VCA. The combination of negative IgG anti-EBNA and low-avidity IgG anti-VCA had a sensitivity and specificity of 100%. The routine addition of IgG anti-VCA avidity estimation to diagnostic EBV serology is recommended.