The clinical diagnosis of DVT is generally thought to be unreliable. However, Wells et al. suggest a well-validated clinical prediction rule which could be used to estimate the pretest probability.
The revised Wells score or criteria for assessment of suspected DVT is mentioned below (with a possible score of -2 to 9):
  | Points  | 
active cancer (treatment within last six months or palliative)  | 1  | 
calf swelling ≥3 cm compared to asymptomatic calf (measured 10 cm below tibial tuberosity)  | 1  | 
collateral superficial veins (non-varicose)  | 1  | 
pitting oedema (confined to symptomatic leg)  | 1  | 
swelling of entire leg  | 1  | 
localised tenderness along distribution of deep venous system  | 1  | 
paralysis, paresis, or recent cast immobilisation of lower extremities  | 1  | 
recently bedridden ≥3 days, or major surgery requiring regional or general anesthetic in the previous 12 weeks  | 1  | 
previously documented deep-vein thrombosis  | 1  | 
alternative diagnosis at least as likely as DVT  | -2  | 
Clinical probability simplified score
The sensitivity for DVT of the Wells criteria is between 77–98% while the specificity is 38–58%. Therefore, it cannot be as the sole diagnostic modality for DVT (2)
Reference:
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