Showing papers by "Emmanuel J. Favaloro published in 1995"

Laboratory Assessment of von Willebrand Factor: Use of Different Assays Can Influence the Diagnosis of von Willebrand’s Disease, Dependent on Differing Sensitivity to Sample Preparation and Differential Recognition of High Molecular Weight VWF Forms

Abstract: Three separate laboratory assays for von Willebrand Factor (VWF), a standard "antigen" (antisera-ELISA-based) assay (VWF:Ag), a standard ristocetin-dependent-platelet-agglutination procedure (VWF:RCof), and an ELISA-based collagen-VWF binding assay (VWF:CBA), have been evaluated for their ability to detect alterations in VWF levels following differential processing of blood for testing, and specifically in (1) serum compared to plasma and (2) filtered plasma compared to nonfiltered plasma. Although all assays tended to detect some change, sensitivity of detection varied between assays, with the VWF:CBA most consistently able to detect large decreases in VWF levels in serum and filtered plasma. The authors propose that the increased sensitivity of the VWF:CBA assay to VWF depleted in these circumstances is that this assay selectively detects higher molecular weight forms (ie, those known to be more functionally relevant), and that assay results reflect the preferential incorporation of these forms in in the platelet-fibrin-gel during the clotting process, and onto the filter matrix during filtration. To confirm this, multimer analysis was performed and showed a reduction in high molecular weight forms of VWF in these cases. Finally, direct evidence that the VWF:CBA assay preferentially detects high molecular weight forms of VWF was obtained following fractionation of normal plasma VWF (separation according to molecular weight using size exclusion matrix; confirmed by specific multimer analysis) and assessment of eluted VWF. Using a standard VWF:Ag assay, detection of eluted VWF was unrelated to molecular size. In contrast, the VWF:CBA showed selective detection, and was able to preferentially discriminate high and intermediate forms of VWF from low molecular weight forms. The findings are of particular relevance to diagnostic pathology laboratories because filtered plasma or serum can be inappropriately (and unknowingly) provided for the clinically queried diagnosis of von Willebrand's disease (VWD). As outlined in this report, these samples can yield VWF results that closely mimic those of a Type 2A or Type 2B VWD individual, and thus, VWD may be incorrectly diagnosed.

Filtered plasma as a potential cause of clinical misdiagnosis: inappropriate testing in a haematology laboratory.

Abstract: We have identified situations in which filtered plasma is provided to the laboratory for combined assessment of lupus anticoagulant, as well as other diagnostic haemostasis laboratory procedures. On the basis of laboratory investigation, however, we report that significant errors in test result interpretation can arise should this occur and depending on the specimen processing procedure, and whether filtered plasma is used for multiple assays. Citrated plasma samples were obtained from 12 normal individuals and a portion of each sample filtered using a standard 0.22 micron filter. Small volumes were frozen for later analysis. We could detect a statistically significant difference (P < 0.01) between filtered plasma and non-filtered plasma in most test results. Most notable were changes in the APTT, fibrinogen, FVIII and vWF, where results often fell outside the normal reference range of the assay. Such assay results closely mimic those obtained with type 2 von Willebrand's disease (vWD) patients, thus should filtered plasma unknowingly be tested for vWF, a wrong conclusion of type 2 vWD could easily arise. Assay results for other parameters may similarly draw incorrect conclusions, such as mild haemophilia A and dysfibrinogenaemia. In summary, we report that following filtration not only are a variety of coagulation test results altered, but reduced plasma levels of some coagulation factors could potentially lead clinicians incorrectly to diagnose congenital or acquired deficiencies or defects. We recommend that laboratories note that (other than for lupus anticoagulant) filtered plasma is not appropriate for the coagulation laboratory, and that any abnormal haemostasis test result following such combined testing be considered a potential artifact and independently repeated to confirm any putative abnormality prior to drawing any clinical conclusions.