Introduction

Twentieth century medical practice placed an emphasis on history and examination skills, as expounded by William Osler. A clinical impression would be formed and laboratory tests would then confirm, refine or refute the diagnosis. This paradigm incorporates the concept of pretest probability — a Bayesian approach whereby the post-test probability of a disease is influenced by the sensitivity and specificity of the test and the pretest probability (ie, likelihood) of the disease.

In modern practice this order is often reversed; test results may be available before the patient is seen. The manner in which results are presented (based on the software used), for example, ‘abnormal’ results in red and ‘normal’ results in black, can lead to an undue binary distinction in the mind of the clinician. Compounding this, often a patient-centred reference range cannot be provided by the laboratory as relevant clinical information is missing. This may lead to misinterpretation of the result (postanalytical error). Inconclusive or abnormal results may lead to a cascade of further investigations to confirm or refute the initial tests.

The historic paradigm of estimating pretest probability, followed by laboratory tests to refine the likelihood of disease, frequently no longer applies. New approaches are needed to remind clinicians that if results are available before a consultation, they must …