Multicentre evaluation of performance of C-reactive protein analysis over a one-year period.

This communication deals with a longitudinal evaluation of C-reactive protein (CRP) analysis during a one-year period using a single lot of liquid control sera (3 levels) (BIOREF-CRP levels 1, 2 and 3) in different laboratories. A total of 652 sets of data were returned from 20 participating laboratories using 13 different reagent-measuring device combinations. The use of the control materials was defined in a standard operating procedure. Data was returned to the organizers on a monthly basis and questions could be asked or problems presented during the evaluation period. Although the performance of different reagents varied, the control materials were shown to be stable over the whole of the evaluation period when stored at 4-7 degrees C in a refrigerator/cold room. Typical problems were encountered, examples of which are presented here in graphical and tabular form.

Thyroid autoantibodies in serum samples with abnormal TSH levels.

Serum samples with normal and abnormal levels of thyrotropin (TSH) were tested for thyroid autoantibodies. Thyroid peroxidase (TPO) antibodies were detected by a radioimmunoassay (RIA) and by an agglutination method, and thyroglobulin (Tg) antibodies by an agglutination method. Elevated levels of TPO antibodies were detected in 47% of samples with abnormal and in 12% of samples with normal levels of TSH (p < 0.001). Sixty-one percent of the biochemically hypothyroid and 26% of the biochemically hyperthyroid samples contained these antibodies (p < 0.001). Tg antibodies were only detected together with TPO antibodies. Testing of TPO antibodies from samples with abnormal TSH levels is discussed.

Hypothyroidism and anti-endothelial cell antibodies.

Because of our previous demonstration of anti-endothelial cell antibodies (AECA) in patients with insulin-dependent diabetes mellitus and their association, in this condition, with thyroid disease, we sought these antibodies in patients with suspected thyroid dysfunction using an enzyme immunoassay with human umbilical vein endothelial cells as the substrate. AECA were found in 5/120 (4.2%) patients with normal and 15/97 (15.4%) with abnormal thyroid function. The increased prevalence in the latter group was due to a highly significant association between the presence of AECA and raised levels of TSH. We conclude that a highly significant correlation exists between the levels of AECA and TSH, but not between those of AECA and fT4. Patients with hypothyroidism as defined by high levels of TSH have AECA significantly more often than patients with low or normal TSH (22.2% versus 2.8% and 5.8%).

Rapid quantification of C-reactive protein by centrifugal analysis.

I describe a rapid, simple immunoturbidimetric method for determining C-reactive protein in serum. With the Instrumentation Laboratory Multistat III microcentrifugal analyzer, quantitative results are obtained automatically after a few minutes of reaction time. Within-run and between-run coefficients of variation ranged from 2.5 to 12.7% at C-reactive protein concentrations of 55 to 69 and 14 to 25 mg/L, respectively, normal values being less than 10 mg/L. Comparison with the commercially available radial immunodiffusion method (y) yields the regression equation y = 1.011x - 2.112 (r = 0.979, n = 100).

Evaluation of a quantitative immunoturbidimetric assay for rheumatoid factors.

A quantitative immunoturbidimetric assay for rheumatoid factors (RF) is described, based on the immunoprecipitation between aggregated human IgG and rheumatoid factors in serum. The resulting turbidity is measured photometrically at 340 nm. The method is standardized against the WHO international reference preparation and the results are expressed in international units per milliliter (int. units/mL). Results correlate well with those by different latex-agglutination techniques (r = 0.80-0.96). The correlation with Waaler-Rose test modifications were 0.75 and 0.92. The within-run and between-run coefficients of variations were respectively from 1.2 to 2.6% and 1.3 to 1.9% for high and low RF concentrations. Quantitative and reproducible results, together with high throughput of samples and compatibility with most clinical chemistry analyzers and photometers, make this new assay well suited for routine screening and monitoring of rheumatoid factors.

Evaluation of a quantitative photometric latex agglutination immunoassay for alpha-foetoprotein.

A simple quantitative photometric method is described for the determination of serum alpha-foetoprotein using latex particle agglutination in an immunochemical system. This method is based on the quantitative photometric measurement of agglutination of latex particles coated with antibodies against alpha-foetoprotein. The turbidity is measured at a wavelength of 340 nm. Agglutination causes a decrease in absorbance. Interference by serum constituents, e.g. rheumatoid factors, are avoided by pretreating the serum samples with buffered polyethylene glycol. Concentrations of 0 to 640 micrograms/l were used for the standard curve. Analytical recoveries were 99.5 to 105.2%. Maximum within and between runs coefficients of variation were 6.2 and 11.6%. The correlation coefficient of the method with radioimmunoassay (RIA), calculated from results on 117 serum samples, was 0.997, and the regression equation y = 0.99x (RIA) - 7.23.

Evaluation of an immunoturbidimetric microalbuminuria assay.

We have evaluated an immunoturbidimetric method for the estimation of urinary albumin. The method, besides being easy to perform and cost-effective, was sensitive enough to detect an even slightly increased albumin excretion (detection limit 5 mg/l). Within-run reproducibility was 1.8 and 2.1%, and between-run reproducibility 2.9 and 4.3% in samples containing 16.1-17.8 mg/l and 50.6-54.0 mg/l of albumin, respectively. The recovery of albumin added to the samples was 98.6-106.6%. Results obtained by this method correlated well with the results obtained by radial immunodiffusion (r = 0.980, n = 44) and radioimmunoassay (r = 0.982, n = 41). The immunoturbidimetric method can be easily adapted for several clinical chemistry analysers.

Measuring rheumatoid factor in nonrheumatoid subjects: immunoturbidimetric assay, latex slide test, and enzyme-linked immunosorbent assay compared.

Previous studies of patients with rheumatoid arthritis (RA) have shown a good correlation between results from immunoturbidimetric assays of rheumatoid factor (RF) and latex fixation tests. To extend the research to non-RA subjects, we tested sera from 1000 pregnant women, half each in the first and third trimesters. By turbidimetry, 24 non-RA sera were regarded as positive for RF (greater than or equal to 20 int. units/mL) and 18 sera as borderline (15-19 int. units/mL). By the latex fixation test, 28 non-RA sera gave a clear reaction (positive) and 17 sera a weak reaction (borderline). The association between the tests was statistically highly significant (P less than 0.001). All sera with positive and borderline reactions were tested by enzyme-linked immunosorbent assay for RF isotypes, together with a random subsample of about one-sixth of the original serum samples. Positive RF results by immunoturbidimetry were predominantly due to the presence of IgM-RF. In contrast to some earlier findings, we saw no difference in the prevalence of positive RF reactions between sera from the first and third trimesters.

Exercise-induced hypoglycaemia in IDDM patients treated with a short-acting insulin analogue.

In order to examine the effect of short-acting insulin analogue on the exercise-induced hypoglycaemia in insulin-dependent diabetes mellitus (IDDM) patients we compared the glycaemic response of 40 min cycle ergometer exercise performed either shortly (40 min) or later (180 min) after a breakfast meal and subcutaneous injection of either short-acting insulin analogue [Lys(B28) Pro(B29)] or soluble human insulin (Humulin Regular) in ten IDDM patients with long duration of the disease. Both preparations had been used 1 month before respective studies. Changes in blood glucose, insulin and counterregulatory hormones were assayed. As compared to human insulin, after the analogue injection the peak insulin concentration came earlier, was 56% higher (p < 0.05) and disappeared faster, and the postprandial blood glucose response was lower (p < 0.05). In the analogue-treated patients the exercise-induced hypoglycaemia was 2.2-fold greater (p < 0.01) during the early exercise, but 46% less (p < 0.05) during late exercise as compared to the treatment with human insulin. Serum insulin or analogue concentration at the beginning of the exercise correlated closely with the fall in blood glucose during exercise (r = 0.74, p < 0.01; r = 0.73, p < 0.02, respectively). In the analogue-treated patients, fasting serum glucagon and adrenalin concentrations were higher than during human insulin therapy (p < 0.05) and remained so throughout the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Automated and manual serum free thyroxine assays evaluated with equilibrium dialysis.

Two fully automated serum FT4 assays (Ciba Corning: ACS-180; Abbott Diagnostics: IMx) and two manual/semiautomated assays (Wallac: Delfia; Diagnostic Products Corp.: Coat-A-Count) were compared with a FT4 reference method based on equilibrium dialysis (ED) using routine clinical samples (n = 105-150). For the full range of FT4 concentrations the correlation with ED was good (r = 0.932-0.959), except for Coat-A-Count (r = 0.852), a single-step analogue-type method. Analytical inaccuracy of the automated methods at low FT4 concentrations was revealed by the differential plot: the IMx assay overestimated concentrations < 10 pmol l-1 and the ACS-180 assay concentrations < 6 pmol l-1. The between-assay CVs for the automated methods were not better than for the non-automated assays indicating problems of calibration curve stability for the automated assays.

Serum carbonic anhydrase III and myoglobin concentrations in acute myocardial infarction.

Serum concentrations of myoglobin (S-Myo) and carbonic anhydrase III (S-CA III; EC 4.2.1.1), a skeletal muscle-specific protein, were measured by RIA in 26 patients with acute myocardial infarction, 14 patients with neuromuscular diseases, and six healthy subjects before and after physical exercise. S-Myo was increased in infarct patients, whereas S-CA III was not altered. In patients with neuromuscular diseases and in healthy subjects after physical exercise, both S-Myo and S-CA III were significantly increased. S-CA III and S-Myo also showed identical peak times, 2 h postexercise. The S-Myo/S-CA III ratio was always higher in infarct patients than in the other groups. Thus, the combination of S-CA III and S-Myo determinations is useful to differentiate whether serum myoglobin is originating from myocardium or from skeletal muscle.