ELISA for determination of total coagulation factor XII concentration in human plasma.

Human blood coagulation factor XII (FXII) is the one chain 80 kDa zymogen form of the active serine protease α-FXIIa, which consists of a heavy and light chain linked by a disulfide bond, the light chain being responsible for the proteolytical activity. FXII is the first component of the contact dependent pathway of coagulation, but its physiological role is still subject to debate. In the present study we utilized two monoclonal antibodies against the heavy chain of FXII to establish a sandwich enzyme linked immunosorbent assay (ELISA) for quantification of total FXII concentration in human plasma samples. A unique characteristic of this assay is its equal recognition of FXII and inhibitor bound FXII. This is important, as inhibitor complexes of α-FXIIa are formed in vivo as well as during blood sampling and handling. Validation of the assay demonstrated a high sensitivity, with a limit of detection and quantification of 1.2 ng/mL and 2.6 ng/mL respectively. The coefficients of variation for the repeatability and within-laboratory standard deviations were 2.6% and 5.2% respectively. The reference interval determined from healthy volunteers (n=240) was 10.6-43 mg/L.

Analytical and clinical validation of a new point-of-care testing system for determination of D-Dimer in human blood.

D-Dimer testing is used for exclusion of deep venous thrombosis (DVT). AQT90 FLEX D-Dimer (AQT D-Dimer) is a novel time-resolved fluorescence based point-of-care test for quantification of D-Dimer in whole blood or plasma. Presently we have determined the analytical and clinical performance of AQT D-Dimer and compared it with four routine D-Dimer assays. The within-run CV of AQT D-Dimer was 3.8-7.2% and the between-run CV was 5.7- 9.7%. Excellent agreement was found between the D-Dimer concentrations recorded in citrate-, heparin- and EDTA stabilised blood. The plasma concentration of D-Dimer was determined with AQT D-Dimer, AxSYM, Biopool Auto-Dimer, STA-Liatest and Vidas New in 170 consecutive patients suspected for DVT. Phlebograms were positive in 64 patients (22 distal, 42 proximal). ROC-curves (ROC), the negative and positive predictive values (NPV, PPV), the sensitivity and specificity of the tests were compared. The area under ROC was comparable for all tests. NPV for all DVT was 87-88%, the sensitivity was 88-92% and the PPV was 45-55%. For proximal DVT the NPV and sensitivity were 100% for all tests, whereas the PPV was 37-48%. For distal DVT we obtained a NPV of 87-88%. The sensitivity was 64-77%, the PPV was 19-24% whereas a specificity of 32-58% was observed. The AQT D-Dimer demonstrates excellent analytical and diagnostic performance. The test is rapidly performed and the measuring range of the assay is wide. The NPV, PPV, specificity, sensitivity and AUC of AQT D-Dimer for both proximal and distal DVT are comparable to routine D-Dimer assays.