From Don Kong, PM Core Lab Supervisor
Children’s Memorial Medical Center
We have a child with a WBC count of 600,000/mcL. The hematocrit with only the RBC mass is 22.8%. However, if the WBC mass + RBC mass is taken into account, the hematocrit jumps to 70%. There is only a small portion of plasma left in the tube. Do I need to adjust the citrate volume in the vacutainer to compensate for the WBC hematocrit of 70? Another question is will this small amount of plasma affect the 1:9 citrate ratio? Does the 1:9 citrate ratio mean 1 part citrate and 9 parts WBC+RBC+plasma?
Hello, Don and thank you for your message. There’s nothing in the books that addresses this unusual situation, but the conclusion is inescapable; you have to adjust the citrate volume to compensate for the proportionally small volume of plasma, regardless of the exact composition of the cellular portion of the blood. If you have a copy of the textbook Hematology: Clinical Principles and Applications, 3rd Edition, you can find a nomogram for computing anticoagulant volume on page 674. The nomogram is designed for preparing a 5 mL specimen.
You can also use the formula:
C (mL) = 1.85 X 10E-3 X (100-HCT[%]) x V (mL)
If you are collecting a standard 3 mL citrate tube, it works out like this:
C (mL) = .00185 X (30) x 3 mL = 0.17 mL
So since you need 0.17 mL of anticoagulant and a standard collection tube is delivered with 0.3 mL, you would need to withdraw 0.13 mL. One tech I know actually uses a tuberculin syringe to withdraw the calculated volume without losing tube vacuum, but most of us just pull the cap and lose the vacuum. In this case, you would have to collect blood using a syringe and transfer approximately 2.83 mL to the tube. Alternatively, you can just make your own specimen tube, in which case you may want to make it up for 5 mL, which is easier to calculate.
You are correct that the 9:1 ratio means 9 parts whole blood to 1 part anticoagulant, but of course the formula changes the ratio for polycythemia. According to CLSI H21-A6, you have to adjust anticoagulant volume for any hematocrit over 55%. Geo