Pulmonary Embolism Clinical Scoring Systems

Evidence-based literature supports the practice of determining the clinical pretest probability of pulmonary embolism before proceeding with diagnostic testing. ^[1] A clinical practice guideline, Current Diagnosis of Venous Thromboembolism in Primary Care, from the American Academy of Family Physicians (AAFP) and the American College of Physicians (ACP), recommends that validated clinical prediction rules be used to estimate pretest probability of pulmonary embolism and to interpret test results. ^{[2, 3]} Clinical scoring algorithms are less objective and less powerful than some authors would claim.

Below are three validated systems: the Modified Wells Scoring System, the Revised Geneva Scoring System, and the Pulmonary Embolism Rule Out Criteria (PERC). ^{[4, 5, 6]} Simplified versions of the Wells score and the revised Geneva score have been developed. Initial studies support the validity of these scores. Points are assigned to each of the criteria.

In 2015, pulmonary embolism guidelines were released by the American College of Physicians and are summarized as follows ^{[7, 8]} :

• Plasma D-dimer tests are more appropriate for those at intermediate risk for a pulmonary embolism, and no testing may be necessary for some patients at low risk.
• Use either the Wells or Geneva rules to choose tests based on a patient's risk for pulmonary embolism.

• If the patient is at low risk, clinicians should use the eight PERC; if a patient does not meet all eight criteria, the risks of testing are greater than the risk for embolism, and no testing is needed.

• For patients at intermediate risk, or for those at low risk who do not meet all of the rule-out criteria, use a high-sensitivity plasma D-dimer test as the initial test.

• In patients older than 50 years, use an age-adjusted threshold (age × 10 ng/mL, rather than a blanket 500 ng/mL), because normal D-dimer levels increase with age.
• Patients with a D-dimer level below the age-adjusted cutoff should not receive any imaging studies.
• Patients with elevated D-dimer levels should then receive imaging.
• Patients at high risk should skip the D-dimer test and proceed to CT pulmonary angiography, because a negative D-dimer test will not eliminate the need for imaging in these patients.
• Clinicians should only obtain ventilation-perfusion scans in patients with a contraindication to CT pulmonary angiography or if CT pulmonary angiography is unavailable.
• Clinicians should use validated clinical prediction rules to estimate pretest probability in patients in whom acute PE is being considered.

See the image below.

Pulmonary embolus.

To see complete information on pulmonary embolism, please see the Medscape Drugs & Diseases article Pulmonary Embolism.

The AAFP/ACP guideline advocates use of the Modified Wells prediction rule for the above-specified estimation and interpretation requirements (see Table 1, below). However, the guideline notes that the Wells rule performs better in younger patients without comorbidities or a history of venous thromboembolism. Current evidence also suggests this tool is effective in pregnant patients. ^[9]

Moreover, the objective components of the Wells (Canadian Pulmonary Embolism Score) criteria have been shown to have little effect on the stratification power of the criteria; virtually all of the classification power is associated with a physician's subjective prejudgment of the likelihood of pulmonary embolism.

Table 1. Modified Wells Prediction Rule for Diagnosing Pulmonary Embolism: Clinical Evaluation Table for Predicting Pretest Probability of Pulmonary Embolism* (Open Table in a new window)

Another validated clinical prediction rule for use in the diagnosis of pulmonary embolism is the revised Geneva score (see Table 2, below). ^[10] The performance of this scoring system appears equivalent to that of the Wells score ^[9] ; however, it should be mentioned that emerging evidence suggests the Wells score to be more accurate. ^{[11, 12]}

The Geneva criteria, which depend only on objective measures, lead to a stratification with a pulmonary embolism prevalence of 8% in the lowest-risk group (Geneva score of 0)—a prevalence too high to be neglected. Table 2. Revised Geneva Score*

Table 2. (Open Table in a new window)

To see complete information on pulmonary embolism, please see the Medscape Drugs & Diseases article Pulmonary Embolism.

In 2008, the Revised Geneva Score was hypothesized to lead to potential miscalculations in the acute setting. Since the variables have different weights, researchers sought to simplify the Revised Geneva Score with equally weighted parameters. Although they were successful in its validation as a clinical decision tool, the study held limitations as a retrospective study, with lack of D-dimer results in all their patients. ^[5] This simplified score should be confirmed in a prospective study prior to its widespread clinical adoption and use. ^[13]

Until now, little evidence-based literature exists analyzing a physician’s approach to a patient with suspected pulmonary embolism. Clinical scoring systems, such as the Wells and the revised Geneva score, have outlined the “what to look for” in medical decision-making, but not the “how to look for.” Emerging evidence worthy of mention illustrates that a physician Gestalt may perform better than sole reliance on clinical scoring systems. ^[14]

This new body of research illustrates the German concept of Gestalt theory, a philosophical and psychiatric principle in which the process is taken into consideration versus the content—in other words, the whole is not the sum of its parts, but greater than the sum of its parts. A physician’s clinical judgment should not be replaced by clinical scoring systems, but should instead be used in conjunction with evidence-based validated systems when deciding the most likely diagnosis for a patient.

It should be noted that clinical Gestalt requires clinical experience and therefore is highly variable between providers. For example, the results of a decision comparing clinical Gestalt between a new intern and a seasoned clinician with a decade of experience is not expected to be the same when compared with a validated scoring system.

In 2004, Kline conducted a prospective study looking at eight variables (see below) to rule out pulmonary embolism when clinical Gestalt was low in the patient with low pretest probability for having pulmonary embolism. ^[6] The rule-out test (with poor specificity of 27% in low-risk patients and 15% in very-low-risk patients) was validated in two studies. ^[15]

Pulmonary Embolism Rule out Criteria (PERC) are as follows:

• Age greater than or equal to 50 years

• Heart rate greater than or equal to 100 beats per minute

• Arterial oxygen saturation (SaO₂) on room air less than 95%

• Venous thromboembolism

• Recent (< 28 days) trauma or surgery

• Unilateral leg swelling

• Hemoptysis

• Oral hormone use

Pulmonary embolism workup can be ruled out if (1) none of the above eight variables is positive and (2) there is a less than 15% (very low) pretest probability that the patient has a pulmonary embolism. A PERC evaluation is considered positive if any one of the eight criteria are met.