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Correction Factor for ACD Solution

On September 28, 2016, Julia Hill asked, “Is there a standard calculation for using ACD tubes?” Her comment was appended to a 2009 entry describing HELLP syndrome, so it may have been buried deep in our database.


George assumes Julia’s question relates to platelet satellitosis, which results from the action of an immunoglobulin potentiated in EDTA, yielding the characteristic blood film appearance and a spuriously low platelet count. The alternative is to collect blood in a blue-closure citrate tube, the same that is used for coagulation assays. The standard plastic blue-closure collection tube contains 0.5 mL of 3.2% sodium citrate and collects 2.0 mL of whole blood, yielding a final volume of 2.5 mL and a total volume to whole blood ratio of 2.5 : 2.0 = 1.25. Multiply the reported platelet count by 1.25 to compensate for the dilution.

Occasionally, satellitosis appears both in EDTA and sodium citrate. My approach in this case has been to collect in a heparinized tube, which relieves us of the need for a correction formula, as the tube is coated with dried heparin. Do the CBC immediately and report only the platelet count from the heparin tube.

I’m not sure if ACD works better than the blue-closure tube, since the anticoagulant is citrate, but maybe the acid pH and the dextrose compensate. Here is Becton-Dickinson’s catalog entry for the ACD tube: “364606–16 x 100 mm x 8.5 mL BD Vacutainer┬« glass whole blood tube. Yellow conventional closure. Paper label. Additive: ACD Solution A of trisodium citrate, 22.0g / L; citric acid, 8.0 g / L; and dextrose 24.5 g / L, 1.5 mL.” Since the ACD volume is 1.5 mL and the total draw volume is 8.5 mL, the ratio of total volume to whole blood is 8.5:7.0 = 1.21. Therefore, multiply the reported platelet count by 1.21 to compensate for the dilution. I hope this helps.

 

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