BACKGROUND Many different cystatin C–based equations exist for estimating glomerular filtration rate. Major reasons for this are the previous lack of an international cystatin C calibrator and the nonequivalence of results from different cystatin C assays. METHODS Use of the recently introduced certified reference material, ERM-DA471/IFCC, and further work to achieve high agreement and equivalence of 7 commercially available cystatin C assays allowed a substantial decrease of the CV of the assays, as defined by their performance in an external quality assessment for clinical laboratory investigations. By use of 2 of these assays and a population of 4690 subjects, with large subpopulations of children and Asian and Caucasian adults, with their GFR determined by either renal or plasma inulin clearance or plasma iohexol clearance, we attempted to produce a virtually assay-independent simple cystatin C–based equation for estimation of GFR. RESULTS We developed a simple cystatin C–based equation for estimation of GFR comprising only 2 variables, cystatin C concentration and age. No terms for race and sex are required for optimal diagnostic performance. The equation, eGFR=130×cystatin C−1.069×age−0.117−7, is also biologically oriented, with 1 term for the theoretical renal clearance of small molecules and 1 constant for extrarenal clearance of cystatin C. CONCLUSIONS A virtually assay-independent simple cystatin C–based and biologically oriented equation for estimation of GFR, without terms for sex and race, was produced.
The fecal calprotectin PETIA, fCal Turbo, is well suited for rapid analysis of fecal calprotectin on Mindray BS-380 or Cobas 501 clinical chemistry analyzers. The test results are commutable with Bühlmann fecal MRP8/14 ELISA.
Serum and plasma calprotectin concentration is shown to be elevated when neutrophils are activated, and may therefore be used as a marker for inflammatory diseases. A serum calprotectin immunoassay was developed based on calprotectin values observed in samples from the intensive care unit. The polyclonal avian antibodies were raised and affinity purified with calprotectin antigens. The performance was tested and it was observed that the assay was linear in the range 0.3–24.7 mg/L, the limit of quantitation was observed to be lower than 0.3 mg/L, no antigen excess was observed up to 54 mg/L, all CVs were lower than 1.8 % in the precision study, the calibration curve stability was longer than 6 weeks, and there was no significant interference detected for haemoglobin, intralipid or bilirubin. The serum calprotectin immunoassay presented in this paper performs well within the criteria carefully set from the limited clinical experience obtained in both serum and plasma. In addition it is commutable with Bühlmann MRP8/14 ELISA.
We have compared three commercial particle enhanced cystatin C reagents. One of the reagents utilizes chicken antibodies and the other two reagents are rabbit antibody based. We show that the chicken antibody based reagent yields a higher delta absorbance when reacting with the antigen. IgY coupled to latex particles show a strong scatter response even at high antigen concentrations in contrast to the steep decline in scatter previously reported for IgY antibodies in solution. The reagent also showed a low CV for duplicate samples. Laying hens thus seems as an interesting source of antibodies for particle-enhanced immunoassays.
Background: A new particle-enhanced turbidimetric immunoassay (PETIA) with avian antibodies for measuring serum/plasma cystatin C has been developed. The performance characteristics of the assay are described.Methods: Measurements were performed on a Roche Modular P and on an Abbott Architect ci8200 using Gentian cystatin C immunoassay.Results: Measuring range was 0.3-8.0 mg/L. Reference range was 0.57-1.09 mg/L. Total analysis time was 10 minutes. Linearity was absolute over the whole assay range. Recovery of samples and controls was within 98.6-109.4%. Total imparticle enhanced nephelometric cystatin C immunoassay (PENIA) by linear regression resulted in a slope within 0.97-1.02 and intercept within ±0.05 mg/L. Interference studies with drugs, anticoagulants, intralipid ( 11g/L), triglycerides ( 14 g/L) and bilirubin ( antibodies, no interference with rheumatoid factor was observed. No carry-over was 6%) were both below 0.33 mg/L, which is less than the lowest standard. Sample stability was up to one month at 2-8°C. Stability of the reagents at 2-8°C was estimated to be 24 months. Stability of the reagents in use was minimum 9 weeks.Conclusions: Gentian cystatin C PETIA is shown to have excellent performance between methods . Interference results are improved due to avian antibodies and a broader span of the calibration curve. Avian antibodies are also known to have better immune response than mammalian antibodies towards mammalian antigens.
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