The Effect of the Order of Draw of Evacuated Blood Collection Tubes on Coagulation Parameters in Normal Volunteers.

Introduction: The recommended order of draw for multiple tube collections (NCCLS [CLSI] H3-A5) clearly indicate that citrate tubes for coagulation tests should be taken before any other tubes (except blood cultures) and that a discard tube should be used if specialised coagulation tests are to be performed. This is to avoid the possibility of tissue activation and the theoretical risk of additive carryover on the parameters being measured. Because of the paucity of published evidence, this study was performed to determine the effect of the order of draw and whether the use of a discard tube is really necessary.

Methods: Three consecutive early morning venous samples were collected into siliconised glass B–D Vacutainers containing tri-sodium citrate (Ref: 367691) from 116 healthy laboratory personnel (F= 74; M = 42) aged 20–63 yrs. Age groups were equally represented. Samples were processed on a Sysmex CA1500 analyser within 1 hour of collection. Appropriate CLSI guidelines were followed throughout. All parameters were measured using Dade-Behring reagents: Activated partial thromboplastin time (APTT) (Actin FSL), prothrombin time (PT) and derived fibrinogen (DF) (Innovin), thrombin clotting time (TCT) (Thromboclotin) and Clauss fibrinogen (CF) (Bovine thrombin and Owren’s veronal buffer). For each parameter, the data from each of the three samples were analysed for significant differences by one way analysis of variance (ANOVA).

Results: Data obtained on measurements of basic coagulation parameters are shown in the table below. SDs are shown in parenthesis. (ns = not significant).

No statistically significant differences were found between the first, second or third samples for any of the measured parameters.

Conclusions: The CLSI recommends an order of draw for evacuated blood collection tubes in order to reduce the possibility of tissue activation in coagulation samples and the theoretical risk of additive carryover on the parameters being measured. Until now, this was based largely on theoretical probability. This comprehensive study demonstrates that the use of a discard tube is probably unnecessary since there is no statistical difference in any of the parameters measured between the first, second or third samples. Although this potentially obviates the expensive use of a discard tube in normal subjects, further work is required to determine whether it is necessary when measuring abnormally prolonged parameters in various pathological states.