To the Editor: In a recent editorial, Gallus estimates the cost of doing ultrasonography in all patients after unilateral hip or knee replacement, with further testing in the 9% or 26% of patients, respectively, found to have deep vein thrombosis (DVT), to be about $200 000 per 1000 patients.1 We agree.

He then states, “Many would argue that extended prophylaxis is likely to be the simplest, cheapest and perhaps safest solution”.

However, prophylaxis is also expensive. Subcutaneous enoxaparin 40 mg administered daily for 30 days costs $170, or $170 000 per 1000 patients.2

In our study, we found DVTs in 1086 of 5999 patients (18.1%) before discharge,3 so that extended prophylaxis would involve 81.9% of patients receiving prophylactic doses of anticoagulants, with the risk of unwanted bleeding, despite the absence of DVT on ultrasound at Day 7 postoperatively.

In addition, if an ultrasound scan was not done before discharge, the 18.1% of patients with a DVT would receive only prophylactic (not therapeutic) doses of anticoagulant for their DVT.

We plan a further study to check the prevalence of post-discharge DVT by repeating ultrasonography at 90 days postoperatively in patients without DVT on ultrasound at Day 7. We suspect the prevalence is lower than suggested in the literature, as the data on late presentation of DVTs have been obtained by retrospective study of the number of patients re-admitted to hospital with DVT.

Finally, on the question of whether performing ultrasonography on all patients has clinical benefit, we concur with Gallus when he writes that “Logic suggests it should . . .”.

In reply: O’Reilly and colleagues belatedly address the need to consider bleeding risk and costs when choosing between management routines designed to prevent venous thrombosis and pulmonary embolism. Their otherwise valuable article1 failed to record bleeding rates when patients (almost 17%) with subclinical calf-vein thrombosis were exposed to therapeutic (not prophylactic) anticoagulant dosages. Nor did they evaluate the dollar and manpower costs of their complex management routines.

Present evidence-based international guidelines from the Seventh ACCP (American College of Chest Physicians) Conference on Antithrombotic and Thrombolytic Therapy recommend effective prophylaxis for at least 10 days in all patients having hip or knee replacement, extending to 28–35 days after hip replacement.2 The ACCP guidelines also recommend against routine use of ultrasound screening because it is “neither clinically effective nor cost effective”.2 This is a Grade 1A recommendation from the ACCP (“Grade 1” implies certainty “that the benefits do, or do not, outweigh the risks, burdens, and costs”; “Grade A” refers to recommendations based on “randomized clinical trials with consistent results [that] provide evidence with a low likelihood of bias”).3 To reverse this recommendation would require randomised comparisons between routine prophylaxis alone or routine prophylaxis supplemented by screening ultrasonography — powered to permit meaningful measures, in both groups, of thromboembolism rates, bleeding rates and costs. Routinely screening for subclinical thrombosis after major joint surgery should not be done outside suitably designed clinical trials until such evidence is available. The role of logic in medicine is to generate hypotheses, which must then be tested by clinical trial. Unfortunately, evidence derived from uncontrolled cohort studies remains limited to Grade C (based on “observational studies or [on] generalization from one group of patients included in randomized trials to a different, but somewhat similar, group of patients”).3