This study demonstrates that despite high rates of clinically compatible signs, DVT prevalence in patients with cellulitis approximates that found in other studies of unselected hospital inpatients where prevalence of symptomatic venous thrombosis has been estimated at 0.6-0.8% [13, 14]. The diagnosis in this study of a greater number of incidental venous thromboembolic events is in keeping with this.
The low prevalence of DVT in patients deemed high risk by the Wells’ criteria suggests that this evaluation tool is not suitable to this patient group. The overlap of clinical signs such as leg swelling reduces the specificity of this tool and the low prevalence adversely affects the positive predictive value of a “high risk” assessment. The very low prevalence of DVT contrasts with those in whom the Wells score was validated in which DVT was found in 27% of the high risk group and 4.3% of the low risk group . All patients included in this study had 2 points deducted from the Wells score, due to the assessment that cellulitis was a more likely explanation for the clinical signs. If this was not done, the overestimation of risk would be much higher and the prevalence of DVT in the high risk group would be 0.6% (95% CI 0.02-3.7%).
In Wells’ study, 2 of 218 patients assessed as low risk and with a negative D-dimer were diagnosed with VTE within 3 months. On the basis of this result, it was asserted that ultrasonography can safely be omitted in this group [9, 15]. The data from this study shows that in patients with cellulitis, prior to any risk stratification, DVT is just as unlikely.
The diagnosis of cellulitis was made solely at the discretion of the treating physician as there are no widely accepted criteria and cellulitis is diagnosed on clinical grounds . It is therefore possible that other illnesses may be misdiagnosed as cellulitis. This uncertainty is an unavoidable aspect of management of cellulitis. There is limited application of the results of this study to those patients at very high risk due to the low number of these patients included. This primarily includes those with a hypercoaguable state, such as those with active malignancy. Anticoagulation will reduce the chance of DVT, but the small number of patients on anticoagulants were included as thrombosis can still occur, especially when anticoagulation is subtherapeutic. A large proportion of patients were taking aspirin but this does not substantially reduce venous thromboembolism . The method of insonation of the femoral and popliteal veins was performed in accordance with current guidelines but only a single ultrasound was performed in the assessment of DVT. It is possible that calf DVTs were missed by this approach and clinical pathways recommend a repeat ultrasound at 5–7 days for those in the high risk group to ensure propagation of calf DVT into the femoral veins has not occurred . No patients were diagnosed with DVT during the 3 months of follow up, which makes this unlikely to have an important affect on the estimated prevalence.