Hemostasis test compatibility with capped and uncapped tubes

The objective of this study was to determine the substantial equivalence of routine and specialty hemostasis testing on capped versus uncapped evacuated blood collection tubes (3.2% sodium citrate tubes, 2.7 ml draw) on assays representing three most common assay types: viscosity, chromogenic, immunoturbidometric. Coagulation instrument manufacturers may provide a list of manufacturers and tube reference numbers that are compatible with their cap-piercing technology on their instruments. However, the use of other blood collection tubes is the responsibility of the user and should be evaluated.

Seventy one volunteers donated two tubes (one each of two manufacturers) and the PT/INR, APTT, fibrinogen, AT and vWF assays were performed first on the capped tube, then on the same tube, uncapped. Assays were performed on the STA-Compact coagulation analyzer with reagents, kits and associated products (calcium chloride, DeSorb U, etc.) provided by Diagnostica Stago, Inc., Parsippany, New Jersey.

The patient specimens were collected at the University Hospital at Stony Brook Outpatient Clinic. Assays were performed in the Stony Brook University, Department of Clinical Laboratory Science Teaching Laboratory. PATIENTS/SPECIMENS: Informed consent was obtained from normal donors, individuals on oral anticoagulant therapy, ages 19 to 85 years, males and females. The Institutional Review Board approved this study (reference number 103249; Principle Investigator: K. Finnegan).

Singlicate values were compared between the samplings from capped and uncapped tubes by linear regression to determine the substantial equivalence. Singlicate measurements were made to maintain sample integrity to complete testing within four hours of the specimen draw.

Linear regression analysis and ANOVA demonstrated a strong correlation between capped and uncapped values with no bias. The correlation coefficient was greater than 0.763 for all assays and the regression line intercept was within acceptable error for the assays (see discussion, biological variation). The p value was greater than 0.08 for all assays.

The authors conclude that there is no significant difference between PT/INR, APTT and fibrinogen analysis on the capped or uncapped blood collection tubes tested in this study. Given the inherent biological variation of AT and vWF, the authors conclude that there is no significant difference between AT and vWF analysis on the capped or uncapped blood collection tubes tested in this study.