PERC Calculator

The Pulmonary Embolism Rule-out Criteria, known as PERC, is a clinical decision rule designed to help avoid unnecessary testing in a narrowly defined group: patients with suspected pulmonary embolism whose pretest probability has already been judged low by a qualified clinician. The rule checks eight findings. A patient is PERC negative only when every finding is absent. If any one criterion is present, the patient is PERC positive and pulmonary embolism cannot be ruled out by this rule alone. The eight criteria are age fifty years or older, pulse at least one hundred beats per minute, oxygen saturation below ninety-five percent, unilateral leg swelling, hemoptysis, recent surgery or significant trauma, previous pulmonary embolism or deep vein thrombosis, and exogenous estrogen use. This calculator derives the first three from entered measurements and adds one point for every marked clinical item. The numeric total is useful for showing how many criteria are present, but the validated decision is fundamentally all-or-none: zero is negative, while one or more is positive. PERC belongs after an initial clinical assessment, not before it. It should not be applied to a patient with moderate or high pretest probability, to someone in whom pulmonary embolism is not genuinely being considered, or as a self-screening test. Depending on the setting, clinicians establish low risk through gestalt or a validated pathway such as a Wells score combined with local guidance. When appropriate use yields a negative PERC result, the residual risk may be low enough that no D-dimer is needed. A positive result usually means the standard diagnostic pathway should continue; it does not establish the diagnosis. Measurements and history require care. Oxygen saturation can be affected by poor signal, motion, nail products, perfusion, altitude, and supplemental oxygen. Tachycardia can have many causes. The surgery or trauma definition and estrogen exposure should follow the protocol used by the treating service. A history of venous thromboembolism includes pulmonary embolism and deep vein thrombosis. Clinical features, pregnancy, postpartum status, anticoagulant use, and local prevalence may affect whether PERC is suitable. Pulmonary embolism can be life-threatening. New unexplained shortness of breath, chest pain, coughing blood, fainting, severe weakness, low oxygen, or a rapid heartbeat requires urgent professional evaluation. Do not use an online score to delay emergency care. This calculator is an educational aid for understanding and implementing the eight-item rule; it cannot examine a patient, establish pretest probability, order testing, or replace local protocols and clinician judgment.