As healthcare costs continue to rise throughout the world, critical assessment of the appropriateness of expenses gain focus. Objectives: We aimed to describe the developments in test numbers of the 10 most frequently requested tests, and to simulate the effect of introducing minimal retesting intervals. Design & Methods: Data from the blood tests – albumin, alanine transaminase, cholesterol, creatinine, C-reactive protein, hemoglobin, hemoglobin A_1c, potassium, sodium, and thyrotropin – from 2,687,589 patients handled by the Capital Region of Denmark from 2010 to 2019 was used. Tallies of each test per year were graphed. A simulation of the effect of minimal retesting intervals on test count and blood sampling volume was performed by virtually removing requests made prior to a set of possible minimal retesting intervals. Results: Increases in requests were observed both from hospitals and general practitioners. The number of requests for hemoglobin A_1c increased more than the other tests. The increases could not be accounted for by an increase in population size and aging of the population, and therefore suggests possible inappropriate increase in monitoring of patients. The simulated effect of applying minimal retesting intervals showed large reductions in tests and blood sampled. Conclusions: For hospitals, the simulation suggested that applying minimal retesting intervals could lead to significant reductions in both the number of blood tests performed and in the amount of blood drawn for testing. For general practitioners, the simulation showed only minimal reductions in number of tests and blood volume drawn.