Effect of Tube Filling Order on Specific Coagulation Parameters in Healthy Subjects

Abstract

B Ba ac ck kg gr ro ou un nd d: : In this study, the authors attempted to determine if there was any effect of tube filling order on both routine (prothrombin time [PT], activated partial thromboplastin time [APTT], and fibrinogen) and specific coagulation parameters (protein S, protein C, antithrombin III, factor V Leiden, plasminogen, and D-dimer).

Discard first tube for coagulation testing

“…Although it is generally accepted that a discard tube is not necessary when drawing samples for PT and APTT testing [9][10][11][12][13][14][15][16][17][18][19], there has been insufficient evidence to date to refute the need for a discard tube when drawing samples for PT determinations on samples with INR values between and over the targeted therapeutic range [11][12][13][14][15]. For the first time, the sample size was high enough for calculation of INRs between targeted therapeutic ranges.…”

“…As tissue thromboplastin may contaminate the first tube sample due to the trauma of the venipuncture, and therefore, affect the accuracy of coagulation testing. This practice was stopped by CLIA after several studies and a new recommendation states that the PT or INR results obtained for normal patients, patients undergoing OAT with warfarin, and normal patient APTT results are not affected if performed on the first tube drawn [9][10][11][12][13][14][15][16][17][18][19]. Today, with modern instrumentation and more specific testing of the common pathway coagulation systems through the use of the PT and APTT, the small amounts of tissue thromboplastin may have less clinical and theoretical importance [15,19].…”

Discard tubes are not necessary when drawing samples for specialized coagulation testing

“…Although it is generally accepted that a discard tube is not necessary when drawing samples for PT and PTT testing [1][2][3][4][5][6][7][8][9][10][11], there has been insufficient evidence to date to refute the need for a discard tube when drawing samples for more specialized coagulation testing [1][2]. In the present study, no statistically significant differences in means (tube 1 versus tube 2) were identified for any analyte by paired t-testing.…”

“…Although the guidelines state that evidence supporting this practice is 'circumstantial at best', the pilot tube is theoretically thought to ensure freely flowing blood and avoid tissue factor activation of coagulation samples. This practice was previously recommended for even routine coagulation testing, but the recommendation was dropped after several studies demonstrated that a discard tube is not required for prothrombin time (PT) and partial thromboplastin time (PTT) determinations [1][2][3][4][5][6][7][8][9][10][11]. Even though the discard tube recommendation persists for certain tests, it is not clear whether this recommendation is always followed in actual practice.…”

“…For example, a study of 57 patients with coagulation parameters within the reference range concluded that a discard tube is not necessary for PT, PTT, fibrinogen, proteins C and S, antithrombin, Factor V Leiden, plasminogen, or D-dimer as no statistically significant differences were identified between two consecutively drawn citrate tubes [8]. However, this study is limited because it did not include clotting factor assays, which are commonly ordered coagulation tests, and evaluated only 'normal' individuals.…”