Wells Criteria for Pulmonary Embolism Calculator

How does this Wells criteria for pulmonary embolism calculator work?

This health tool is based on the Wells score which is a clinical prediction model for the likelihood of pulmonary embolism. There are several versions of this model, the one used in this Wells criteria for pulmonary embolism calculator being the most common.

Once all the clinical criteria is evaluated and answers yes or no are selected in each of the 7 measurements, the calculator will provide a result taking into consideration two of the interpretations of the Wells score, including a pulmonary embolism risk probability percentage.

There is also a simplified version in which all criteria if met are awarded 1 point each instead of different points.

Wells criteria explained

This scoring system for pulmonary embolism has proven to be of great relevance in cases where PE is suspected, however this is not a diagnosis tool and should be used in conjunction with laboratory testing such as the D-dimer test or imagistic. The Wells score only stratifies patients for PE and estimates pre test probability. Criteria used are as follows:

1. Clinical signs and symptoms of DVT – meaning symptoms of deep venous thrombosis such as unilateral swelling of one leg or pain.

2. An alternative diagnosis is less likely than PE – considering there are other relevant symptoms such as shortness of breath or chest pain and the differentiated diagnosis still points mainly towards PE.

3. Tachycardia present (heart rate >100 bpm) – rapid heart beat can indicate there is a blockage in the arteries and blood flow is impaired at some level.

4. Immobilization for the past 3 days or surgery previous month – bed rest in convalescence or any surgery presenting risk of blood clot development should be taken in consideration.

5. History of DVT or PE – history of such conditions in the family is considered an important risk factor.

6. Hemoptysis present – although hemoptysis is a recognized PE symptom, the underlying causes might be different in some causes, varying from ventricular systolic heart failure to severe mitral stenosis.

7. Malignancy in treatment or palliative – cancer is a risk factor in PE.

Wells scoring interpretation

There are two parallel interpretation systems of the Wells score, a two tier and a three tier one.

1. Two tier suggests that scores above 4 are likely to be followed by a pulmonary embolism diagnosis and scores of 4 and below are unlikely to carry this diagnosis.

2. The three tier interpretation suggests that scores below 2 have a positive diagnosis probability of less than 15%, scores between 2 and 6 have a moderate risk of 29% while score above 6 carry a high risk of over 59%.

Main causes and risk factors of PE

PE is defined as a blockage in the main artery of the lung or one of its branches, usually because of a particle (embolism) arriving through the blood stream from a different part of the body, most often due to deep venous thrombosis (DVT) which is the presence of a blood clot in one of the veins of the leg.

Prolonged bed rest in convalescence is considered a risk factor as well as family history of VTE, DVT or PE. Hormone substitution therapies such as the contraceptive pill are also said to increase the change of blood clots.

PE symptoms and diagnosis

Pulmonary embolism is a serious condition that has certain marker clinical signs but also other signs that are similar to other health conditions as serious so a differentiated diagnosis is essential. Amongst the symptoms that are sudden in onset there is dyspnea chest pain, increased heart beat, low blood oxygen saturation, low blood pressure, fainting, loosing consciousness.

Diagnosis usually combines clinical observation with laboratory tests (the D-dimer test) and imaging (CT pulmonary angiography). The D-dimer is a blood test that evaluates the existence of FDP (fibrin degradation product) a fragment found after a blood clot is degraded thus showing thrombosis.

CT pulmonary angiography shows the pulmonary arteries and is mainly used in diagnosing such embolisms.

References

1) Wells PS, Anderson DR, Rodger M, et. al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer. Thromb Haemost. 2000 Mar; 83(3): 416-20.

2) Goldhaber SZ (2005). Pulmonary thromboembolism. In Kasper DL, Braunwald E, Fauci AS et al. Harrison's Principles of Internal Medicine (16th ed.). New York, NY: McGraw-Hill. pp.1561–65.