Order sets could serve as a form of decision support for laboratory testing. They could assist the physicians and their patient in making an informed decision on which tests to order for a given indication. Literature suggests that one in three ordered laboratory tests are inappropriate. Inadequate testing may influence quality of care negatively. Further research therefore is needed regarding the potential effects if order sets would be implemented in GP practice.

Also, there is evidence in literature suggesting that the use of order sets may reduce the amount of ordered lab tests, however there is no evidence as to whether such interventions would lead to more appropriate lab tests ordered by general practitioners.

The primary objective of the KCE trial is to compare the effect of a patient group for which order sets will be applied versus a control group for which routine care (i.e. same laboratory facilities, but no order sets) will be applied, on the proportion of appropriate laboratory tests ordered by primary care physicians on 17 common indications, based on the guidelines as developed by EBM Practice Net. The secondary objectives are based on the comparison of the evidence-based order sets vs. the control group:

• To investigate the incidence of missed or delayed diagnoses for 17 indications;
• To investigate the number of laboratory tests with no restrictions on indications;
• To investigate the effect of amongst others the cost-effectiveness and of the implementation of evidence-based order sets on the downstream activities

Previous research was aimed at investigating the effect of a Clinical Decision Support System (CDSS) limited to one or a few indications. Previous research also showed that a CDSS aimed at multiple indications seems to be more effective than those aimed at a single or few indications. Therefore, the researchers of the KCE Trial will introduce a database of 17 common indications to evaluate the effect of these order sets on appropriateness and diagnostic errors. Additionally, this KCE Trial will investigate the cost-effectiveness of the implementation of evidence-based order sets. In particular, the effect on the downstream activities, which is assumed to be larger than the direct effect on the tests themselves (Ulysses effect), will be investigated. By doing so for a subgroup, the researchers might gain more insight in these downstream activities.

Any patient who is a client of one of the physician practices which will provide data is eligible. At patient level, there will be no further inclusion or exclusion criteria apart from a signed informed consent. For the criteria for the participating GPs, see section ‘Data providers’.

It is planned to recruit about 13,000 patients.