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Evaluation of a new venom‐based clotting assay of protein C
Author(s) -
COOPER P. C.,
COOPER S. M.,
GOODFELLOW K. J.,
HICKEY K. P.,
KITCHEN S.,
MAKRIS M.
Publication year - 2008
Publication title -
international journal of laboratory hematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.705
H-Index - 55
eISSN - 1751-553X
pISSN - 1751-5521
DOI - 10.1111/j.1751-553x.2007.00972.x
Subject(s) - chromogenic , protein c , protein s , clotting time , antigen , lupus anticoagulant , venom , coefficient of variation , medicine , microbiology and biotechnology , immunology , chemistry , biology , biochemistry , antibody , chromatography , platelet
Summary Congenital protein C deficiency significantly increases the risk of venous thromboembolism, a serious and potentially lethal condition. Protein C levels can be determined by chromogenic, clotting and antigenic assays, each type of assay has differences in specificity and sensitivity to protein C deficiency. In principle, clotting‐based assays of protein C are preferred over chromogenic assays, as they can detect some rare mutations that are missed by the chromogenic assay, however, clotting‐based assays may be prone to inaccuracy because of poor specificity. We have evaluated a new venom‐based clotting assay of protein C, and optimized it for use on Sysmex CA‐1500 analyser. The assay was linear from 0 to 130 U/dl, a normal plasma demonstrated good inter‐assay precision, with a coefficient of variation of 4.8%. The assay compared well with antigenic‐ and venom‐based chromogenic protein C assay in normal individuals, subjects with lupus anticoagulant, and subjects with FV Leiden. Median protein C levels by clotting, chromogenic and antigen for the three subject groups were 108 U/dl, 108 IU/dl and 109 IU/dl for normal subjects, 94 U/dl, 106 IU/dl and 103 IU/dl for subjects with lupus anticoagulant, and 102 U/dl, 104 IU/dl and 100 IU/dl for subjects heterozygous for FV Leiden. Comparing levels of clotting protein C with protein C antigen by ratio (clotting/antigen), the three groups showed small differences that did not quite reach statistical significance, (mean ratios ranged from 0.95 to 1.01, anova P = 0.0561), the lowest ratio was with the lupus anticoagulant group. Comparing clotting assay with chromogenic assay by ratio (clotting/chromogenic), the three groups did show a statistically significant difference ( P = 0.0033) which was due to a difference in mean ratios between normal and lupus anticoagulant groups (ratios 1.00 and 0.91, respectively, P < 0.01). There was no statistical difference in any of the groups when comparing chromogenic protein C with protein C antigen (mean ratios ranged from 1.02 to 1.05, P = 0.3925). In a normal sample, the clotting‐based protein C level was unaffected by increasing FVIII level by up to 1000 IU/dl, using intermediate purity FVIII concentrate. The new assay is considered to be a suitable assay for the routine diagnosis of protein C deficiency.