Elevated plasma levels of D-dimer have been found to be a useful screening tool in the diagnosis of deep venous thrombosis (DVT) in the general population. In the post operative setting however their role is less clear. The majority of NHS trusts use D-dimer as a prerequisite test prior to radiological imaging to diagnose DVT.

Aims and method: This study evaluates the effectiveness of D-dimer as a screening tool for DVT in the postoperative period following total hip and knee arthroplasty.

Plasma D-dimer levels were measured pre operatively and on post operative days 1, 3, 5, and 7 in 78 patients undergoing primary total hip or knee arthroplasty. On day 7 patients underwent bilateral duplex ultrasound scanning in order to confirm the absence of DVT. All patients wore pneumatic foot pumps for DVT prophylaxis. Chemical thromboprophylaxis was not used.

Results: D-dimer levels in the post operative period were characterized by a double peak, on days 1 and 7. Mean day 1 value 3.63 (sd=2.72), mean day 7 value 2.83 (sd=1.58). Mean values on days 3 and 5 were 2.52 (sd=2.26) and 2.45 (sd=1.41)

Comparing D-dimer levels between hip and knee arthroplasty we found that both groups displayed the same trend in post operative D-dimer levels; however levels were significantly higher following knee replacement.

We compared D-dimer levels of these patients with a second group of 43 patients who had a confirmed DVT following hip or knee arthroplasty. The mean D-dimer level in this group was 2.20 (sd=0.98 or range 0.80 – 4.46). This group was subdivided into two groups, those with D-dimer samples before day 8 and those after. We found a significant difference between the groups (p=0.01). Mean < day 8 = 2.70. Mean ³ day 7 = 1.97.

The group of patients with Confirmed DVT before day 8 were compared with those free of clot. There was no significant difference found between the D-dimer levels of the two groups. (p=0.37).

Conclusion: The D-dimer level is never normal (< 0.4mg/l), in the week following total hip or knee replacement and so cannot exclude a DVT. The level it rises to is indistinguishable form that seen in the population with a DVT and so cannot identify those patients in whom further investigation is warranted. Requesting a D-dimer test in this population wastes time and resources and is of no benefit.