Prompting physicians for cost-effective test ordering in the low prevalence conditions of family medicine.

We have developed a computerized prompting system for test ordering which we feel will decrease the cost of investigations and at the same time promote an evidence based learning approach to test ordering. Prompting systems have been shown to be cost-effective but suffer from many disadvantages in the family practice setting. They tend to be difficult to modify by the user and contingent on an inflexible rule based structure. Many suggestions are ignored implying that they are not relevant. In family practice most conditions are of low prevalence. Prompting for test ordering where the pre-test likelihood of disease is small will result in a large number of false positives and many unnecessary repeat or confirmatory investigations and attendant anxiety unless the prompting system is specifically designed to be used in a low prevalence environment. PROMPTOR-FM (PRObabilistic Method of Prompting for Test ORdering in Family Medicine) was developed to overcome these perceived difficulties. It allows the physician to rapidly calculate the positive and negative predictive values of a test being considered based on the clinical index of suspicion. The physician is able to repeat the calculations and compare the results with previous calculations. By using PROMPTOR-FM repetitively, the clinician can learn to balance the risk of "missing" a rare but serious condition against the risk of falsely identifying disease with its downstream hazards and costs of further investigation. Prompting for test ordering is therefore uniquely tailored to each patient's situation.