Reliability of the third-generation recombinant immunoblot assay for hepatitis C virus

BACKGROUND: In a confirmatory laboratory, the second-generation recombinant immunoblot assay (RIBA-2) was replaced by the third- generation RIBA (RIBA-3) in March 1993. The aim of this validation study was to compare the sensitivity and specificity of RIBA-2 and RIBA- 3 in a routine setting, by using a validated hepatitis C virus (HCV) RNA polymerase chain reaction to establish plasma viremia. STUDY DESIGN AND METHODS: RIBA-2 testing was performed (March 1991-March 1993) in 593 HCV RNA-positive and 1498 HCV RNA-negative subjects. RIBA-3 testing was performed (March 1993-May 1994) in 220 HCV RNA-positive and 530 HCV RNA-negative subjects. All samples reacted for anti-HCV in enzyme- linked immunosorbent assay. RESULTS: In HCV RNA-positive individuals, the sensitivity of RIBA-3 was significantly higher than that of RIBA-2 (99.5% vs. 93.3%, p = 0.0005). This was not caused by inclusion of the NS5 antigen, but by a higher sensitivity of the antigens c33 and c100 (RIBA-2: 94.3% and 62.6%; RIBA-3: 99.5% and 88.6%). Replacement of the c22 and c100 recombinant proteins by synthetic peptides significantly reduced nonspecific reactivity against these antigens (p < 0.0001). Unfortunately, increased nonspecific reactivity against the modified c33 antigen and the new NS5 antigen canceled out this effect. Two-band reactivity occurred more often in nonviremic persons than in viremic persons (32.7% vs. 8.2%, p < 0.0001). Risk factors for HCV infection were less frequently observed in 11 blood donors with two-band reactivity than in 6 blood donors with other positive RIBA-3 patterns (18% vs. 83%, p = 0.03). CONCLUSION: The higher sensitivity of RIBA-3 significantly reduced the number of indeterminate test results in HCV RNA-positive persons. Confirmatory laboratories must be aware of the frequent occurrence of nonspecific, isolated reactivity and even nonspecific, two-band reactivity in anti-HCV enzyme-linked immunosorbent assay-reactive blood donors.     

Report on the development of a procedure to prevent placement of feeding tubes into the lungs using end-tidal CO2 measurements

OBJECTIVE: To determine the accuracy of a technique using capnography to prevent inadvertent placement of small-bore feeding tubes and Salem sump tubes into the lungs. SETTING: Twelve-bed medical intensive care unit (MICU) in a 557-bed teaching hospital. PATIENTS: A total of 25 ventilated adult MICU patients were studied-5 in phase 1 and 20 in phase 2. DESIGN: Phase 1 tested the ability of the end-tidal CO2 (ETCO2) monitor to detect flow (and thus accurately detect CO2) through small-bore feeding tubes. A small-bore feeding tube, with stylet in place, was placed 5 cm through the top of the tracheostomy tube ventilator adapter in five consecutive patients. The distal end of the feeding tube was attached to the ETCO2 monitor. The ETCO2 level and waveform were assessed and recorded. Because CO2 waveforms were successfully detected, a convenience sample of 20 adult MICU patients who were having feeding tubes placed (13 Salem sump tubes, 7 small-bore feeding tubes) was then studied. The technique consisted of attaching the ETCO2 monitor to the tubes and observing the ETCO2 waveform throughout placement. RESULTS: The study hypothesis was supported. Of the seven small-bore feeding tubes tested, all were successfully placed on initial insertion. Placement was confirmed by absence of an ETCO2 waveform and by radiograph. Of the 13 Salem sump tubes, 9 were placed successfully on first attempt and confirmed by absence of CO2 and by air bolus and aspiration of stomach contents. ETCO2 waveforms were detected with insertion of four of the Salem sump tubes; the tubes were immediately withdrawn, and placement was reattempted until successful. CONCLUSIONS: The technique described is a simple, cost-effective method of assuring accurate gastric tube placement in critically ill patients.