Clinical decision rules

Clinical decision rules (CDRs) are a set of condition-specific history, examination and often laboratory findings that can indicate the likelihood of a particular condition in a clinically significant way. The presence or absence of each feature is used to estimate the overall relative probability of a condition.

This is in the context of deciding if a patient either :

• has no or a low risk of significant pathology and is therefore unlikely to benefit from further testing and/or diagnostic imaging
• needs further imaging to clarify the probability of a particular condition
• can commence treatment for a given condition without further imaging or testing

Because of the standardized nature of CDRs, they help to reduce interobserver variability and the subjectivity of assessments .

CDRs should be applied with caution or not at all in some patients, depending on the original population that the CDR was developed on. The simplified Wells score, for example, has never been validated in pregnant women and there are alternative scores for this situation (the LEFT clinical prediction rule) . Other issues that can influence the use and implementation of a CDR include local availability, considerations of radiation exposure, the monetary cost of the imaging study, renal function (in the case of iodinated contrast or gadolinium studies) and patient preference. The best CDRs are those that have both been shown to be used in clinical practice and reduce the cost of healthcare or amount of imaging examinations .