Summary
Study objective. To determine whether levels of thrombin-antithrombin III (TAT) in
plasma, taken two weeks pre-operatively, predict the development of deep vein thrombosis
(DVT) in patients undergoing major hip or knee surgery.
Design. Prospective cohort.
Setting. Tertiary-care referral centre, university-affiliated hospital.
Patients. Ninety eight consecutive patients undergoing elective hip or knee surgery.
Intervention. All eligible consenting patients were seen in a preoperative clinic
two weeks prior to surgery and had blood taken for measurement of plasma TAT level.
After surgery, they received a combination of unfractionated heparin 5000 Units 12-hourly
subcutaneously, and antiembolism stockings (TEDS), as prophylaxis against DVT. Contrast
venography was performed prior to discharge, and according to the results, patients
were classified as having proximal (popliteal and/or more proximal) DVT (n = 12),
calf DVT (n = 7) or no DVT (n = 79).
Measurements and Results. The mean TAT level was significantly higher in patients
who developed DVT (5.7 μg/l) than in those who did not (4.1 μg/l), p = 0.035. Using
cut-points of 3.5 and 5.5 μg/l for the TAT level, patients could be categorized as
high, intermediate, and low risk for the development of DVT. The proportion of patients
with TAT levels of ≥3.5μg/l who developed calf or proximal DVT was significantly higher
than the proportion of patients with TAT levels of <3.5 μg/l who developed calf or
proximal DVT (p = 0.02). The proportion of patients with TAT levels >5.5 μg/l who
developed proximal DVT was significantly higher than the proportion of patients with
TAT levels of ≤5.5 μg/l who developed proximal DVT (p = 0.03).
Conclusions. This study demonstrates that pre-operative TAT levels correlate with
the risk of developing DVT after major orthopedic surgery. Further studies are needed
to determine the reason(s) for this observation and whether rational recommendations
about prophylaxis and screening for DVT can be made based on the results of a pre-operative
TAT level.
