Just having an IV in place for an hour elevates your D-dimer

From First 10 EM:

Did everyone know that placing an IV can elevate D-dimer levels and increase false positives? Apparently we should, as this paper is more than 20 years old. This study included 20 healthy volunteers who had no risk factors for thromboembolism. They placed a 20 gauge IV in the antecubital fossa of all participants, took blood through that IV immediately to count as the baseline, and then 90 minutes later they performed a blood draw from the opposite arm. There was a statistical increase in D-dimer after the IV had been in place for 90 minutes, but the difference is miniscule (15 ng/mL vs 33ng/mL, p=0.04) and so I would probably have considered it clinically insignificant. However, the difference in false positives really stood out to me. There were 2 (10%) false positives on the immediate draw, but 5 (25%) on the blood draw at 90 minutes. Although this difference was not statistically significant, it certainly seems like it could be clinically significant. Of note, D-dimer values were probably artificially low in this study, because in addition to looking at young healthy volunteers, they handled the specimens with a perfect protocol (storing them on ice) that isn’t routinely followed in clinical practice. I don’t know if anyone out there applies this information clinically, or how you would. I haven’t seen any follow-up data. I was sort of hoping Jeff would respond on Twitter and just tell me how to interpret this study, but it hasn’t happened yet.

Bottom line: This is a very small study using only healthy volunteers, so take it with a grain of salt. However, it probably makes sense to try to ensure your DDimer is taken on the first blood draw, rather than after the patient has had an IV in place for hours in the ED.

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