Vasopressin analogues. Their role in disorders of hemostasis

Laboratory Assessment of von Willebrand Factor: Altered Interpretation of Laboratory Data, and Altered Diagnosis of von Willebrand's Disease

Three laboratory assays for von Willebrand Factor (vWF), namely, (i) a standard "antigen" [antisera-enzyme-linked immunosorbent assay (ELISA)-based] (vWF :Ag), (ii) a standard ristocetin-dependent platelet agglutination procedure (vWF:RCof), and (iii) a newly developed ELISA-based functional vWF collagen binding assay (vWF:CBA), were coevaluated. We (a) assessed their ability to detect vWF under different assay conditions and (b) reevaluated normal vWF reference ranges using citrated plasma from >200 normal individuals. The following effective normal reference ranges were derived: vWF-Ag (40-200%), vWF:CBA (50-400%), and vWF:RCof (45-200%). Based on other laboratory data, caution is indicated in the interpretation of "borderline" or "equivocal" test results (e.g., 35-55%), since these may derive from normal individuals or from vWD patients. In addition, our study shows that selection of different assay conditions, different test plasma dilutions, or different test sample processing methods can also lead to differences in the "apparent" levels of detected vWF. For example, using plasma from 100 normal individuals processed as "test samples," we determined that higher sample dilutions tended to provide lower (dilution factor adjusted) assay results in the case of the vWF:Ag and vWF:CBA, and higher assay results in the case of the vWF.RCof, with greater differences noted in test samples containing higher levels of vWF. The explanation for these findings relate to the assay design. Thus, in the diagnostic laboratory, the standard vWF:Ag, vWF:CBA, and vWF:RCof assays procedures are designed to provide calibration curves that are "upward linear" in the (vWD) clinically important region of 0-50% of normal, with a plateau tending at higher vWF levels. Using these standard methodologies, and standard plasma dilutions, high-vWF level test samples will tend to fall on or near the plateau, and results will be unreliable, with a tendency to be exaggerated the higher the vWF. These findings have particular relevance to research studies measuring vWF in patients suffering various clinical conditions (e.g., thrombotic thrombocytopenic purpura, diabetes, renal failure) where higher than normal levels of vWF may be anticipated. In these cases, laboratory-derived vWF levels could be "misrepresented" if the study design did not take into account the need to revise the vWF testing procedure. Key Words: von Willebrand factor-von Willebrand's disease—Laboratory assessment-Normal ranges—Reference ranges—Diagnosis.

von Willebrand's disease: use of collagen binding assay provides potential improvement to laboratory monitoring of desmopressin (DDAVP) therapy

This report describes studies investigating the use of a collagen binding assay to improve the laboratory monitoring of desmopressin (DDAVP) therapy in patients with von Willebrand's disease (vWD). We evaluated the response of seven patients with vWD (four type I, three type IIA) to DDAVP, administered using a standard protocol, by assessing levels of von Willebrand factor (vWF) and factor VIII, as well as performing skin bleeding times (SBT) prior to, and at sequential time points following, DDAVP administration. The study employed the following assays: von Willebrand factor antigen assay (vWF:Ag; determined by ELISA); a novel functionally based collagen binding assay (CBA; determined by ELISA); ristocetin cofactor assay (RCof; determined by platelet aggregometry); von Willebrand factor multimer analysis (using SDS-agarose gels); factor VIII coagulant (FVIIIC; determined by clotting assay); and factor VIII antigen (FVIIICAG; determined by ELISA). All patients showed an initial incremental increase in vWF/FVIII levels using all assays above, and some showed some correction in SBT. Although the absolute levels of vWF/FVIII antigen or activity varied between patients, the CBA was found to provide consistently the greatest proportional incremental increases (i.e., -fold) compared to baseline (pre-DDAVP) levels. Accordingly, we consistently observed an increase in the CBA to vWF:Ag ratio for all patients evaluated. This supplements previous findings that have suggested a unique ability of our CBA procedure to bind preferentially to higher molecular weight (i.e., more functionally active) forms of vWF. We therefore propose that the use of the above test combination (e.g., vWF:Ag plus CBA) may provide the basis for more accurate estimation of a patient's functional responsiveness to DDAVP therapy in future studies.

Hemostasis in renal disease: pathophysiology and management

The hemostatic abnormalities commonly encountered in patients with renal disease can significantly threaten the well-being of the patient and pose difficult management issues for the clinician. In this review, we explore the pathophysiology underlying the bleeding diathesis and hypercoagulability that can occur. Current therapeutic interventions are also discussed.

von Willebrand's disease: laboratory investigation using an improved functional assay for von Willebrand factor

This report details extensive studies investigating an improved screening procedure for the laboratory confirmation of clinically suspected von Willebrand's disease (vWD). Over the past two years, over 400 plasma samples, comprising samples derived from both normal individuals (n = 112) and from patients undergoing investigation on clinical grounds, underwent analysis in this screening procedure, comprising three distinct assays: a standard ELISA assay for von Willebrand Factor (vWF) antigen levels (vWF:Ag), a standard ristocetin cofactor (R Cof) assay, and a functional collagen based ELISA assay for vWF ('CBA'). Normal individual plasma samples yielded normal reference values (mean +/- 2SD) approximating 50-200% (vWF:Ag, R Cof) or 50-250% (CBA). In order to permit comparative analysis, and based upon derived assay values, and subsequent multimer analysis, patient samples were either deemed to derive from persons unlikely to suffer vWD ('non-vWD' patient group) or those potentially suffering vWD. The latter group was further separated into subgroups based upon the likelihood, and probable subtype of vWD. In conjunction with the vWF:Ag assay, the CBA provides the basis by which an effective predictor system (likelihood and probable subtype of vWD) can be offered on the basis of preliminary screening procedures. To date, there has been no overlap in vWF:Ag to CBA ratios (vWF:CBA) between patients yielding Type II vWD like multimer patterns and those yielding Type I vWD, or normal, multimer patterns. Thus, high vWF:CBA (i.e. > or = 3.0) would suggest a Type II, or pseudo, -vWD like defect, whereas low vWF:CBA (< or = 2.5) would likely derive from either normal individuals, or persons suffering from Type I vWD.(ABSTRACT TRUNCATED AT 250 WORDS)

Severe hyponatremia after repeated intravenous administration of desmopressin

Desmopressin (DDAVP) has recently been found to improve hemostasis in patients with congenital or acquired disorders of coagulation and to reduce operative blood loss in patients with normal hemostasis undergoing certain surgical procedures. Despite its potent antidiuretic effect, severe hyponatremia after the intravenous administration of DDAVP is felt to be rare. We report four cases of severe hyponatremia with serious clinical sequelae occurring in patients with underlying coagulopathies who were treated prophylactically with DDAVP to improve hemostasis prior to surgical procedures. Each patient received multiple (3-22) doses of DDAVP and was given intravenous hydration with hypotonic solutions before developing clinical signs and laboratory evidence of hyponatremia. We believe that the risk of significant hyponatremia after treatment with intravenous DDAVP may be higher than is generally appreciated and that patients undergoing surgical procedures, who often receive multiple doses of DDAVP and intravenous hydration, are at particular risk for this complication. Hypotonic intravenous solutions should be avoided and serum sodium levels should be monitored frequently in those patients receiving multiple doses of DDAVP.