An evaluation of the Coulter Counter Model T660.

An evaluation of a Coulter Counter Model T660 has been carried out. This instrument is a compact, fully automated, blood cell counter which measures WBC, RBC, Hb, haematocrit, MCV and platelet count on a 100 microliter sample of whole blood. The instrument was assessed during one month of regular use. One possible microbiological hazard was detected, which could be corrected by an instrument modification. No mechanical hazards were identified. The instrument as supplied produced some inaccurate WBCs; this malfunction appeared to be consequent on a design fault relating to the burn circuit of the white cell aperture and following instrument modification performance was considerably improved. Results produced were broadly comparable with those produced by a Coulter Counter Model S Plus IV. Precision was satisfactory. Deviations from linearity on dilution were not sufficient to be of practical importance. Carryover was satisfactorily low. Time-lapse of up to 48 h did not introduce inaccuracy of sufficient magnitude to be of practical importance. Throughout varied from 52 to 63 specimens/h. Following instrument modification the overall assessment was that the T660 was easy to operate, reliable, and clinically useful.

Assessment of the value of a competitive protein binding radioassay of folic acid in the detection of folic acid deficiency.

The diagnostic value of the Becton Dickinson Radioassay Kit (125I) for the 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.

An assessment of the Coulter Counter Models S Plus II and III.

The Coulter Counter Models S Plus II and III have been evaluated. No serious safety hazards were identified. Scientific assessment showed some non-linearity in the Hb which caused the MCH and MCHC to vary as samples were diluted. Precision and carry-over were satisfactory. The results obtained compared well with those of the Coulter Counter Model S, except for WBC; reference methods showed better accuracy on the Models S Plus II and III. Platelet counts agreed with those by phase-contrast microscopy and the lymphocyte percentage was similar to that from the blood film except in the lymphoproliferative disorders. The whole blood and pre-dilute modes gave similar results though the platelet count was slightly higher in the whole blood mode. In the National External Quality Assessment Scheme results were in accordance with those from other Model S Plus Users. Time did not allow a detailed evaluation of the cell volume distribution curves but it was noted that the white cell profile was useful for detecting platelet aggregation. Efficiency assessment showed throughputs of 66 and 93 samples per hour on the Models S Plus II and III respectively. The platelet count was clinically useful as was the lymphocyte percentage measurement which rendered some differentials unnecessary. Rejection of the white cell profile was a helpful index of abnormality on the Model S Plus II but occurred non-specifically on the Model III tested.

Assessment of a radioisotopic assay for vitamin B12 using an intrinsic factor preparation with R proteins blocked by vitamin B12 analogues.

A competitive protein binding radioassay kit for serum vitamin B(12) has been assessed. Precision, linearity, sensitivity, and specificity have been found to be satisfactory. Falsely-normal assay results in patients with vitamin B(12) deficiency have not been observed.