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.

Fibrinogen.

Fibrinogen is the final essential building block of the clotting process. Thus, all of the preliminary "cause and effect" events in the clotting cascade rely on the work of this molecule to measure their success. The most commonly used laboratory method for measuring fibrinogen is the Clauss fibrinogen assay. The Clauss fibrinogen assay is a quantitative, clot-based, functional assay. The assay measures the ability of fibrinogen to form fibrin clot after being exposed to a high concentration of purified thrombin. Plasma samples are pre-diluted which minimize assay interference from substances like heparin and fibrinogen degradation products. In brief, the diluted plasma is incubated at 37°C prior to the addition of the pre-warmed (37°C) thrombin reagent. From the exact moment of the addition of thrombin, the time to clot is measured. The clotting time in seconds is interpolated from a standard curve made using various dilutions of assayed standard plasma. The following chapter includes detailed information on the Clauss fibrinogen assay. Other fibrinogen assays used include fibrinogen levels derived from prothrombin time assays and antigenic methods. Fibrinogen measurements using the prothrombin time and antigenic based assays are described in brief.

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.

Coronary artery bypass surgery with heparin-coated perfusion circuits and low-dose heparinization.

OBJECTIVE: To evaluate the safety and efficacy of heparin-coated perfusion circuits with low-dose heparinization and centrifugal pumping compared with the standard method during coronary artery bypass grafting. DESIGN: Prospective, randomized, single-blind clinical trial. SETTING: A primary care institution. PATIENTS: Ninety patients who underwent first-time elective coronary artery bypass grafting were eligible for the study. After giving informed consent, they were randomly assigned to 1 of 3 groups (30/group). INTERVENTIONS: Perfusion on regular uncoated bypass equipment with a roller pump and full-dose heparinization (300 IU/kg bolus, activated clotting time [ACT] > 400 s) (group 1), on a heparin-coated oxygenator with a centrifugal pump and full-dose heparinization (group 2) and on fully heparin-coated bypass equipment with a centrifugal pump and low-dose heparinization (100 IU/kg bolus, ACT of 180-400 s) (group 3). Standard coronary artery bypass grafting was performed. OUTCOME MEASURES: Postoperative bleeding, transfusion requirements and clinical outcomes. RESULTS: There were no complications related to the study protocol. Study groups were similar in terms of postoperative bleeding, transfusion requirements and clinical outcomes. CONCLUSIONS: Heparin-coated cardiopulmonary bypass with low-dose heparinization and centrifugal pumping is a safe practice but showed no advantages over the use of regular uncoated bypass circuits for coronary bypass surgery.