Giant cell arteritis (GCA) is one of the prime emergencies in ophthalmology.  The "gold standard" confirmatory test for GCA is temporal artery biopsy (TABx), although ultrasound and MRI are making inroads.  Knowledge of the pretest and post-test probabilities of GCA can aid management decisions regarding glucocorticoids and the need for investigations.  We provide a 10 factor externally validated pretest calculator for patients with suspected GCA.  We tabulate the posttest probabilities for GCA using Bayes theorem and the results of published meta-analyses for TABx, ultrasound and MRI.
      Risk articulation is a fundamental aspect of shared decision making and evidence-based patient choice.  Although probabilities are by definition uncertain, the pretest and post-test calculations provide an objective estimation of risk boundaries, which can help clinicians and patients with suspected GCA decide whether to continue with glucocorticoids, and/or pursue further tests.

The post-test probability of giant cell arteritis after ultrasound, MRI, or negative biopsy

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