From our summer, 2014 Quick Question, What is your policy for managing overfilled coagulation specimen tubes?
a. We reject overfilled tubes; results are likely to be invalid. 116 votes, 69%
b. We accept overfilled tubes; overfilling doesn’t affect results. 28 votes, 17%
c. We never see overfilled tubes. 24 votes, 14%
CLSI Guideline H21-A5 specifies that coagulation tubes must be filled to at least 90% capacity or to the tube manufacturer’s lower limit to avoid relative anticoagulant excess, given the blood to anticoagulant ratio should be 9:1. H21-A5 also requires that specimens whose hematocrit exceeds 55% be collected in an adjusted anticoagulant volume, again to avoid an excess anticoagulant to plasma ratio. However, the guideline makes no reference to overfilling. It also states there are no data that support the need to raise anticoagulant volume for specimens whose hematocrit is less than 20%. By inference, it appears there is little harm in overfilling a tube, thus decreasing the anticoagulant to blood ratio.
However, the 116 respondents who reject overfilled tubes may be using overfilling as a surrogate for poor specimen management. It may be, for instance, that a syringe was overfilled and the excess whole blood forced into the evacuated tube, implying the possibility of hemolysis if transferred too forcefully, or clotting if the transfer were delayed. Another, somewhat less likely possibility is that the specimen was collected piecemeal and small volumes were added together. In either event, specimen integrity could be called into question.
Conversely, it may be that a number of rejected specimens could have been used without compromising the results, particularly if the operator carefully inspected for clots, thus cutting down on recollects. I will be interested to learn about your experience.