Alejandro Zuretti

Comparison of conventional lateral-flow assays and a new fluorescent immunoassay to detect influenza viruses

Sofia, a novel, fluorescent lateral-flow immunoassay was compared with two conventional colorimetric assays, Quickvue Influenza A+B and Directigen FLU A+B, to identify influenza viral antigen from patient nasopharyngeal specimens. A total of 118 frozen original influenza-positive specimens and 57 prospective specimens were examined. Using rt-PCR as a referee assay, sensitivity values (%) for influenza A/B of 80.0/74.8, 73.3/59.3 and 73.3/40.7 were obtained using the Sofia, Quickvue and Directigen assays, respectively. All assays demonstrated reduced sensitivity for influenza B as compared with influenza A virus. With respect to the Sofia assay, the sensitivity of influenza B for the Directigen assay was significantly diminished. False positive results were not observed in the Sofia and Directigen assays. The Quickvue assay produced 3 false-positive results (2 influenza A and 1 influenza B) resulting in a specificity (%) of 96 and 98 for influenza A and B, respectively. Cross-reactivity to other respiratory viruses was not observed among immunoassays. A sensitivity rank (highest to low) of rt-PCR>culture>Sofia>Quickvue>Directigen was established using dilutions of influenza A and B. Sofia provides enhanced sensitivity and objective result interpretation over conventional colorimetric immunoassays.

Evaluation of respiratory syncytial virus (RSV) direct antigen detection assays for use in point-of-care testing

RSV infections cause lower respiratory tract infections and result in surges in physicians office, emergency department visits and hospitalizations, especially in infants and toddlers. Point-of-care (POC) testing reduces healthcare costs and permits informed decisions on treatment, however, optimal POC assays must be sensitive, easy to perform and provide rapid results. A prospective study tested 230 patient nasopharyngeal specimens using 4 RSV direct antigen detection assays (Directigen, Quickvue, Sofia and Veritor) and RT-PCR. A RSV dilution study was also performed to evaluate sensitivity. RSV fluorescent antibody testing in 46/230 patients was also evaluated. Sensitivity values obtained for the Sofia, Veritor, Directigen and Quickvue assays (%) were 85, 72.5, 70 and 57.5, respectively. Fluorescent result interpretation may account for Sofias enhanced sensitivity. Specificity (%) was 97-100 among assays. Sensitivity data were confirmed in the dilution studies. Fluorescent antibody testing demonstrated 64% sensitivity compared with RT-PCR. Objective result reporting, walk away testing and high sensitivity make the Sofia a valuable choice for POC testing. Veritors sensitivity may also render it acceptable in POC. Lack of objective results by Directigen and the poor sensitivity observed by Quickvue may preclude their value in diagnostic testing.

Comparison of the Sofia and Veritor Direct Antigen Detection Assay Systems for Identification of Influenza Viruses from Patient Nasopharyngeal Specimens

ABSTRACT Influenza antigen detection assays (Sofia fluorescent immunoassay [FIA] and Veritor) yield objective results, which are potentially useful for point-of-care testing. The assays were evaluated with reverse transcriptase PCR (RT-PCR) using 411 nasopharyngeal swab specimens. Sensitivity and specificity values (percentages) of 79.0/99.0 and 64.0/99.4 for influenza A and 92.9/96.7 and 78.6/98.7 for influenza B were obtained for the Sofia and Veritor assays, respectively.

Stability of values for the activities of critical enzymes assayed in serum

OBJECTIVES Our medical center laboratory receives frozen clinical chemistry samples from outlying hospitals for which assays for critical enzyme activities are requested. Our objective is to determine the effects of freezing (-20°C) on these enzyme activities in samples over a one month period. METHODS Enzyme activities for ALP, AST, ALT, CK and LD for 30 patients sera were stored at-20°C and were assayed on a Beckman-Coulter AU5800 analyzer at 0, 15 and 30 days after collection. Statistical tests were performed to determine if the values were statistically the same or different. RESULTS F-tests for all five enzyme levels showed no statistically significant differences (p>>0.05); linear regression analysis showed high correlation of results (r>0.99 for all correlations) with some bias for ALT. CONCLUSIONS We conclude that the activities of these enzymes are stable, except possibly ALT, when stored frozen at -20°C over the 15- and 30-day storage periods.

MP8: MONOCLONAL GAMMOPATHY CHARACTERIZATION USING SERUM PROTEIN ELECTROPHORESIS IN A MAJOR URBAN POPULATION

Purpose of Study Serum protein electrophoresis (SPEP) with subsequent immunofixation (IF) are clinical laboratory techniques used to evaluate a wide-range of disorders where abnormal serum protein quantities are characteristic (e.g. multiple myeloma (MM), MGUS, amyloidosis, HIV/AIDS, SLE, CLL/NHL). Thus, it is important to identify or exclude malignancy when considering the analyses. Our aim is to characterize SPEP patients from our institution, a predominantly black population. Methods Used We retrospectively reviewed 50 patients SPEP/IF results. Data recorded were SPEP/IF results, monoclonal immunoglobulin (Ig) identity, clinical diagnoses, age, race and gender. Univariate analysis was used to describe patient demographics. Parametric analysis was used to compare the monoclonal gammopathy (MG) group versus non-MG group. Summary of Results Age range was 12–86 years, mean age was 62 years and male to female ratio was 1:3.5. Forty-eight (96%) patients identify as black, 1 (2%) Asian and 1 (2%) white. SPEP patterns showed 1 (2%) patient had acute inflammation, 3 (6%) had chronic inflammation, 24 (48%) were inconclusive, 16 (32%) had MGs, 3 (6%) had normal results and 3 (6%) had polyclonal bands (table 1). Among MG patients, IgG was most common isotype (75%), kappa was most common light chain (58%) and IgG kappa was most common (44%). Mean age was 69 years for MG patients and 58 years for non-MG patients. MM was identified in 9 (18%) patients; 89% (8/9) had normal total protein (TP) levels and 1 (11%) had increased TP. Neuropathy was seen in 7 (14%) patients; 71% (5/7) had polyclonal gamma Ig increase, and 1 (14%) case with co-HIV infection had monoclonal IgG kappa. Seven (14%) patients had CKD, 4 (8%) had HIV/AIDS, 3 (6%) had anemia, 3 (6%) had MGUS, 1 (2%) had SLE and the remaining 16 (32%) had other co-morbidities (i.e. HTN, DM, CAD, etc.). Conclusions SPEP/IF analyses were used to characterize 50 patients. A wide-range of disorders were observed. MG patients were 11 years older than non-MG patients. IgG kappa was most common MG. Our study showed female-predominance. This study shows SPEP utility to discern various disorders observed at our institution. Abstract MP8 Figure 1