Q: While drawing blood for the coagulation profile, what should be the ratio of citrate solution to whole blood in the tube to have an accurate result?
Answer: 1:9
The objective of the above question is to bring to light the errors which can occur at multiple levels and may give wrong results and render patients to undue transfusions.
In USA the recommended tube for coagulation profile is with the 'blue top'. It is filled with 3.2 percent sodium citrate solution. To get the ratio of 1:9 between the citrate solution and the whole blood, the tube must be filled within 90 percent of the full collection volume. If the tube is not properly filled, it will disequilibrate the 1:9 ratio leading to an inaccurate results. Above said, in patients with polycythemia some of the citrate should be removed due to a reduced plasma volume, to attain the 1:9 ratio.
Tubes should be gently inverted a few times to mix the citrate solution with the blood. Shaking of the tube will cause the hemolysis.
Also, the tube should be tested in a timely manner as factors V, VIII and protein S can be degraded quickly. And, tubes should not be frozen prior to separation of plasma from cells.
#hematology
References:
1. Adcock DM, Kressin DC, Marlar RA. Minimum specimen volume requirements for routine coagulation testing: dependence on citrate concentration. Am J Clin Pathol 1998; 109:595.
2. Chuang J, Sadler MA, Witt DM. Impact of evacuated collection tube fill volume and mixing on routine coagulation testing using 2.5-ml (pediatric) tubes. Chest 2004; 126:1262.
3. Zürcher M, Sulzer I, Barizzi G, et al. Stability of coagulation assays performed in plasma from citrated whole blood transported at ambient temperature. Thromb Haemost 2008; 99:416.
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