Linda Stang

Warfarin Monitoring in Patients With Anticardiolipin Antibodies, But Without Lupus Anticoagulants

Misleading international normalized ratios (INR) may be obtained from anticoagulated patients with lupus anticoagulants (LA). As a result, special precautions have been suggested for oral anticoagulant dosing. It is possible that plasma from subjects with an anticardiolipin antibody (ACA) without an LA could also affect the INR. We have studied nine such subjects who were anticoagulated and compared them with 11subjects who had neither antibody. The INR was performed, using local specific ISIs, with 11 different thromboplastins. No substantial difference was seen between the ACA-positive and ACA-negative patients, for either individual thromboplastins or patients. We similarly measured INRs in eight nonanticoagulated patients with ACAs. No effect on the INR results was observed. Thus, in these anticoagulated and nonanticoagulated patients we detected no evidence of any effect of an ACA on the INR.

Dabigatran assessment in patients with acute complications using routine coagulation assays.

Complications while on dabigatran therapy, particularly bleeding and thrombosis, are occurring, and require laboratory assessment. The utility of routine coagulation assays has been previously evaluated in stable patients, but not those with acute complications. The purpose of this study was to determine how to employ routine coagulation assays to assess dabigatran in patients with acute complications. Seventeen patients on dabigatran presenting with various complications were evaluated. In addition, plasma samples with various fibrinogen levels were spiked in vitro with dabigatran ranging from low trough levels to the highest supratherapeutic concentrations reported (5000 ng/ml). INR, partial thromboplastin time (PTT), thrombin time (TT, Diagnostica Stago reagent), and fibrinogen were assayed and results compared to that of the Hemoclot Thrombin Inhibitors assay. Interference in the Clauss fibrinogen assay was assessed using a variety of commercial reagents. The majority of patients on dabigatran with acute complications demonstrated a significant negative bias in PTT results compared to normal plasma. TT remained highly sensitive to the presence of dabigatran (at least 10 ng/ml) under all circumstances investigated. There was wide variation in the sensitivity of commercial fibrinogen assays to dabigatran, with some even showing interference in the therapeutic range but this could be mitigated. The PTT is unreliable as a method for assessment of dabigatran in patients with acute complications. The TT assay is a simple and reliable alternative, particularly when combined with a fibrinogen level.

D-dimer and fibrinogen/fibrin degradation products.

Although clinical requests for D-dimer are generally in the minority of assays in the routine clinical laboratory, they are an important aspect-especially if the laboratory supports an active emergency room and hematology service. Throughout the literature, D-dimer assays have been used for many purposes in the research setting; however it is generally the negative predictive value of the assay that is the most common piece of information being utilized from the standpoint of a clinician. Research or clinical needs will dictate the type of assay required-a qualitative, semiquantitative, or quantitative D-dimer assay may be appropriate for a particular purpose. Commonalities and differences between these assay types are outlined here, as well as universal concerns regarding standardization of D-dimer assay results.

Specimen Requirements for the Haemostasis Laboratory

Sample integrity is one of the most important details to consider for the production of quality results in the laboratory. Many factors have the potential to adversely affect the sample: intrinsic patient characteristics (caused by the underlying malady and/or treatment, incorrect patient preparation, etc.), difficult or incorrectly performed collection of sample, correct timing of sample collection relative to drug administration, incorrect processing and transport within the laboratory-just to name a few. This chapter outlines standard common requirements with explanations as a basis for those limitations, and practical laboratory advice to attain and maintain dependable samples.