Comparison of Low Volume and Conventional Sodium Citrate Tubes for Routine Coagulation Testing

Low-volume sample tubes reduce unnecessary blood loss due to repeated blood collection and are more convenient to collect blood from patients with difficult veins. However, different sample tubes may be sources of preanalytical bias, and the corresponding test results may reflect clinically important differences. We compared the new low-volume sodium citrate tube to the conventional sodium citrate tube to determine any significant differences between the two types of tubes for routine coagulation testing.

We collected blood samples from 48 random patients, who were referred for routine coagulation testing, into low-volume (1 mL) and conventional (2.7 mL) sodium citrate tubes. We assayed the samples for prothrombin time (PT), activated partial thromboplastin time (aPTT), and D-dimer using the automated coagulation analyzer.

There was excellent correlation (r > 0.97) between the results of the two tubes for PT, aPTT, and D-dimer. The PT and aPTT for the low-volume sodium citrate tube were significantly shorter than those of the conventional sodium citrate tube. There was no statistically significant difference in the results for D-dimer. The percent biases calculated with Bland-Altman analysis were 0.8% for PT and 2.0% for aPTT. Both of them were within the desirable specifications for bias with 2.0% for PT and 2.3% for aPTT.

It is imperative to perform local validation before introducing new sodium citrate tubes into the routine blood collection practice. Every laboratory needs to standardize the procedures for evaluation of these tubes.