ASSESSMENT OF DIAGNOSIS OF DEEP VENOUS THROMBOSIS OF THE LOWER LIMBS USING ESTIMATION OF CLINICAL PROBABILITY

The value of a diagnostic test (or test combination) depends not only on its sensitivity and specificity but also on the prevalence of the disease. In the present study, we have re-assessed the value of the clinical diagnosis in a group of 45 consecutive patients suspected of deep venous thrombosis (DVT) of the lower limbs. The clinical probability (CP) of the diagnosis was estimated on a clinical basis alone (history and clinical examination) by trained physicians (2-month training in an Angiology Unit). Afterwards, the diagnosis of DVT was established using the combination of Doppler ultrasounds and venous occlusive plethysmography. Venography was performed when the non invasive techniques were inconclusive.

DVT was found in 14 patients (31 %). In the 21 patients in whom CP was ⩽ 0.20, there was no DVT. In the 10 patients in whom CP was ⩾ 0.80, DVT was confirmed in 9 cases. When CP was between 0.21 and 0.79, a DVT was found in 5 out of 14 patients.

Thus, when CP is ⩾ 0.80 or ⩽ 0.20, further investigation does not seem to provide additional diagnostic information. The estimation of CP by a trained physician allows to define a subgroup of patients in whom the clinical diagnosis is valuable.

Two third of the patients in our series belong to this subgroup. In one third of the patients, CP was intermediate and non invasive tests or venography are necessary.

Since the range of clinical probability in which clinical diagnosis is reliable will depend on both the physician and the recruitment of the patients (medical or surgical, ambulatory or hospitalized), it must be determined in each center.