[en] Since the presence of analogues of vitamin B₁₂ (B₁₂, cobalamin, Cbl) has been postulated as the basis for the high values obtained by some radioisotope dilution assays (RIDA) of serum Cbl, serum was examined for analogues. None could be demonstrated in the extracts of serum prepared for RIDA as sought by both direct and indirect techniques. The natural forms of serum Cbl were converted to cyanocobalamin (CN Cbl) by this process of extraction which included cyanide (CN). The correctly performed RIDA for Cbl based on R binder gave higher values than a RIDA based on intrinsic factor or than by bioassay. By exclusion, the difference appeared to be due to unidentified factors rather than the presence of analogues. (author)

[en] A method for the measurement of circulating ferritin concentrations by direct radioimmunoassay is presented. The method described is simple to operate, precise, and sensitive and is suitable for the routine diagnostic measurement of ferritin in either plasma or serum. (author)

[en] Letter to the editor

[en] The diagnostic value of the Becton Dickinson Radioassay Kit (¹²⁵I) for the assay of red cell folate has been investigated. The assay was acceptable with regards to precision but was non-linear with changing packed cell volume. Sensitivity of the assay was satisfactory, with 24 of 25 folate deficient patients giving red cell folate values which fell below the reference range. Specificity of the assay in the detection of folate deficiency was less satisfactory. As with microbiological assays, a considerable proportion of vitamin B₁₂ deficient patients had low red cell folate values. In addition, low concentrations were found in 12% of patients who were unlikely to be deficient in either vitamin B₁₂ or folic acid. (author)

[en] The interference of IgM-class rheumatoid factor (RF) in the solid-phase radioimmunoassay (RIA) of rubella virus IgM antibodies was studied. Acute rubella infections did not significantly activate RF. False-positive rubella antibody results were obtained, however, when patients with raised RF levels were tested. If a low rubella IgG antibody titre was present, a high level of RF was required to cause a false-positive IgM result; conversely, in sera with high IgG titres, only a low level of RF was required for interference. Although the false-positive IgM titres obtained were generally low, they did show a positive correlation to both RF levels and rubella IgG titres. False-positive results were successfully avoided by removing the RF by absorption with heat-aggregated human gamma globulin. The absorption procedure did not affect true rubella IgM antibody titres. (author)

[en] Three serological methods, radioimmunoassay (RIA), latex agglutination (LX), and counter-current immunoelectrophoresis (CIEP), for sensitivity in the detection of the capsular polysaccharide antigen of Haemophilus influenzae type b or Neisseria meningitidis groups A and C were compared. RIA was consistently the most sensitive, LX the next, and CIEP the least sensitive. When RIA and LX were used to test cerebrospinal fluid (CSF) samples of patients with meningitis, they gave very similar results. In only two out of 47 samples, in which RIA detected one of the three antigens, was the amount of the specific polysaccharide too low to be detected by LX. By the serological methods evidence of specific pathogen could be detected in 49 samples, including nine from patients who had received intensive antimicrobial treatment for up to three days and from whom specimens yielded no bacteria on culture. The reactions were specific in all cases except two out of 47 tests positive to LX. From these two CSF samples N. meningitidis group B could be cultivated, whereas the LX was recorded positive for N. meningitidis of group A in one case, and of group C in the other. The nonspecific reactions could be due to antibodies to bacterial components other than the capsular polysaccharide. (author)

[en] A commercial kit for the radioisotopic assay of folate in serum, the Bio-Rad 'Quanta Count' folate kit, produced lower results than the Lactobacillus casei microbiological assay method. Its normal range was 2.0 to 13.0 μg/l and the reproducibility was similar to that of the microbiological assay method. The kit was also satisfactory for whole body folate assays. The cost requires careful consideration before the kit is used for routine purposes. (author)

[en] Five commercial kits for the determination of folate and six kits for the determination of vitamin B₁₂ were investigated. Their performance has been compared with microbiological methods for the two vitamins and with a non-commercial radioisotopic method for B₁₂. The results show the importance of the determination of the reference range for an individual laboratory for each method. The precision of the kits varied appreciably, as did their performance using specimens from patients with different haematological disorders. In particular, certain kits failed to detect all patients with pernicious anaemia. The relative accuracy of the kits was assessed. Various factors which should be taken into account in the final selection of a satisfactory kit are discussed. (author)

[en] Serum folate estimates were generally comparable using the three methods, although the ⁷⁵Se radioassay kit (Radiochemical Centre, Amersham, UK) gave somewhat lower results. Inbatch variations of the manual methods reflected the number of dilution stages. The tube assay and radioassay required similar technician time, but the practical size of a tube assay batch was potentially much larger. The automated method involved less than half the time of the other two methods. The cost per sample using the radio-isotope kit was between 10 and 30 times greater than with the automated technique. (U.K.)

[en] In patients with Crohn's disease and ulcerative colitis, alterations in serum storage temperature produced significant changes in serum lysozyme activity (SLA) as measured by the lysoplate method. This was not the case in healthy controls or in a group with other gastrointestinal disorders. Electrophoretic separation of serum revealed two components of lysozyme-type lytic activity but only one in extracts of gut mucosa, leucocytes, and egg white. The major lytic component of serum migrated towards the cathode and reacted with specific antilysozyme serum, but the minor component which migrated towards the anode did not. Although the cause of this anionic lytic activity is uncertain, it contributes to total serum activity as estimated by any method utilising the lysis of Micrococcus lysodeikticus, and may possibly be related to the observed thermolability. (author)