Immunoglobulin isotype identification in red cell antibodies using flow cytometry.

BACKGROUND: Identifying the isotype of an immunoglobulin (IgM vs. IgG) detected in a patient sample is especially important in anticipating the risk of hemolytic disease of the newborn. Currently, 2-mercaptoethanol (2-ME) treatment of a sample is used in the authors' laboratory to degrade IgM, and this is followed by retesting. This method has multiple drawbacks. The purpose of this study was to develop a flow cytometry (FC) assay that would replace the 2-ME treatment protocol (2-ME treatment). STUDY DESIGN AND METHODS: A preliminary FC assay was developed, modified, and refined through the use of stock antibodies. Then, 10 samples containing antibodies were tested in parallel by the FC assay and 2-ME treatment. RESULTS: When a 10-unit mean channel fluorescence change was used as an index of a positive result, the FC assay detected all isotypes identified by 2-ME treatment. The FC assay was also able to identify mixtures of isotypes. One antibody that had not reacted in conventional agglutination testing was detected by the FC assay. The amount of fluorescence and the agglutinating strength of the antibody did not parallel each other. In one case, this discrepancy may have reflected an antibody that was primarily IgA. CONCLUSIONS: The FC assay appears to be as accurate as 2-ME treatment in differentiating IgG from IgM. The FC assay produces a positive endpoint for both isotypes, will identify IgA, requires less sample, and has no odor.

Open access fibresigmoidoscopy: a comparative audit of efficacy.

A total of 541 open access referrals for fibresigmoidoscopy over five years were compared with 495 hospital initiated procedures during the same period. The number of open access fibresigmoidoscopies doubled during the five years but diagnostic yield remained unchanged at about 40% and was similar to that of the hospital initiated procedures. Colorectal carcinoma was seen in 64 open access patients compared with 47 hospital referred patients, the proportion of Dukes's type A lesions being similar (34%) in both groups. Polyps, colitis, and diverticular disease were equally common in open access and hospital referred patients. Fibresigmoidoscopy failed to detect disease in only 12 patients (1.2%) and the procedure was unsatisfactory in only 54. Referral was considered justified in 475 (88%) open access patients, and only 54 (17%) patients with normal appearances at endoscopy required further investigations. Diagnostic yields were low (19%; 30/156 cases) in open access patients under 40 and in patients with abdominal pain, constipation, or abdominal pain with constipation (0-17%). Most of these young patients presumably suffer from the irritable bowel syndrome and do not justify fibresigmoidoscopy. In contrast, there was a high diagnostic yield (90-100%) in patients of all ages referred for diarrhoea and rectal bleeding, altered blood from the rectum, and rectal bleeding associated with abdominal pain. Open access fibresigmoidoscopy is an effective service that should be freely available to general practitioners.

Salmonella testing of pooled pre-enrichment broth cultures for screening multiple food samples.

A method has been described for testing multiple food samples for Salmonella without loss in sensitivity. The method pools multiple pre-enrichment broth cultures into single enrichment broths. The subsequent stages of the Salmonella analysis are not altered. The method was found applicable to several dry food materials including nonfat dry milk, dried egg albumin, cocoa, cottonseed flour, wheat flour, and shredded coconut. As many as 25 pre-enrichment broth cultures were pooled without apparent loss in the sensitivity of Salmonella detection as compared to individual sample analysis. The procedure offers a simple, yet effective, way to increase sample capacity in the Salmonella testing of foods, particularly where a large proportion of samples ordinarily is negative. It also permits small portions of pre-enrichment broth cultures to be retained for subsequent individual analysis if positive tests are found. Salmonella testing of pooled pre-enrichment broths provides increased consumer protection for a given amount of analytical effort as compared to individual sample analysis.