Single-dose LMWH can interfere with algorithm for DVT diagnosis

(HealthDay)—A single dose of low-molecular-weight heparin (LMWH) given the previous day can reduce D-dimer and potentially risk non-identification of a deep vein thrombosis (DVT), according to a research letter published online Dec. 15 in the International Journal of Laboratory Hematology.

Peter M. Baker and David M. Keeling, M.B., Ch.B., from the Oxford Haemophilia and Thrombosis Centre in the United Kingdom, examined whether a single dose of LMWH given in the community when a patient presented to their general practitioner too late in the day for referral would render the D-dimer algorithm unusable the following morning. Paired samples were collected for D-dimer estimation from 50 patients pre-administration of LMWH and on presentation to the DVT clinic the following morning.

The researchers found that the sample taken post-administration of a single dose of LMWH showed a significantly lower D-dimer, from 2,670 µg/L to 2,274 µg/L (16.4 percent reduction; P < 0.01). Reduction in D-dimer crossed the normal range of <500 µg/L fibrinogen equivalent units in four patients and would have altered their management in the clinic assessment. These patients could have been denied an ultrasound scan, which was indicated, if the clinic D-dimer had been used, and a DVT could have been missed.

"If a D-dimer is to be used as part of a diagnostic algorithm, a sample must be taken prior to administration of LMWH," the authors write.