Effects of Tourniquet Technique, Order of Draw, and Sample Storage on Plasma Fibrinogen

Abstract

The use of plasma fibrinogen concentrations to predict clinical ischemic events in subjects with and without prior evidence of atherosclerosis (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) has led to recommendations to incorporate fibrinogen into the cardiovascular risk profile (15). Such use of plasma fibrinogen requires careful attention to potential sources of variability, as only small (5%) absolute differences in fibrinogen distinguish subjects who develop cardiovascular disease from those subjects who do not (16). Variability in fibrinogen results apart from intraindividual differences is difficult to quantify, because the few groups who have examined these issues used different assays for fibrinogen determination. Moreover, the functional assay for fibrinogen is highly influenced by technician expertise and manipulation (17). Previously, we examined within-run analytical CV, within-person, within-day biological variation, and a 6-week within-person biological variation with the Clauss method for fibrinogen determination (16). We describe here selected effects of sample collection and storage on fibrinogen results and we propose guidelines for sample collection and storage. Blood was collected in evacuated tubes (5-mL capacity) containing 0.5 mL of 0.129 mol/L (3.8%) buffered citrate solution (Becton Dickinson). Fibrinogen concentrations were determined by thrombin clottable time with the Clauss method (Dade Data-Fi, Baxter Diagnostics) (18) with bovine thrombin (100 kU/L) and 2.8 × 10−2 mol/L sodium barbital in 0.125 mol/L sodium chloride. Duplicate plasma samples were diluted 1:10 (by vol) with an imidazole buffer (Organon Teknika) and measured at 20- and 40-s intervals at 37 °C in a fibrometer (Model BBL, Becton Dickinson). All samples were acquired from healthy, nonsmoking volunteers who were seated ≥5 min before phlebotomy (19). Volunteers were excluded if they had current illnesses, regular …