The Pulmonary Embolism Rule-Out Criteria (PERC) calculator is designed to determine the likelihood of a pulmonary embolism (PE) based on specific clinical criteria. The calculator evaluates eight inputs, each representing a condition or risk factor associated with PE, assigning a score to responses and consequently interpreting the results to assess the likelihood of PE.

The inputs and their associated criteria are as follows:

- Age >= 50
- Heart rate >= 100
- SpO2 < 94%
- Unilateral leg swelling
- Hemoptysis
- Recent surgery within 4 weeks
- Prior pulmonary embolism or deep venous thrombosis
- Oral hormone use

Each criterion corresponds to a boolean input and contributes a score of 1 if true (indicating the presence of the condition or risk factor). The total possible score ranges from 0 to 8.

The computation process involves checking each criterion and adding a score of 1 for each true response. The final score is the sum of these contributions.

Interpretation of results is straightforward:

- If the total score is 0, it indicates that pulmonary embolism is unlikely.
- If the total score is 1 or higher, there is a likelihood of pulmonary embolism.

The Pulmonary Embolism Rule-out Criteria (PERC) is a clinical prediction rule used to exclude pulmonary embolism (PE) as a diagnosis in patients with low pretest probability. It is specifically designed for use in adult patients who are suspected of having a PE but are deemed to be at low risk based on clinical judgment. 

The PERC rule is a useful tool in the emergency department setting, as it helps to avoid unnecessary diagnostic testing, such as D-dimer testing or computed tomography pulmonary angiography (CTPA), in patients who are unlikely to have a PE. 

The PERC rule should not be used in patients with a high pretest probability of PE, or in patients with signs of right ventricular strain or hypoxia. It is also not applicable to pregnant women or patients under the age of 18.

Pulmonary embolism rule-out criteria (PERC)