Beginning in the late 19th century, technologic innovation gave results of laboratory investigations an increasingly prominent role in diagnosis and treatment. Our current concept of chronic kidney disease, for example, depends largely on laboratory findings.1 However, the optimal frequency of testing has been established rigorously in few if any clinical situations. In particular, the practice of testing dialysis patients monthly, rather than at some other frequency, does not reflect any evidence that this practice optimizes either patient-centered outcomes or incremental cost-effectiveness.