Preventing chronic diseases is an essential aspect of medical care for healthy patients, but deciding when to collect information, such as the patient’s cholesterol levels, is difficult. Measuring too frequently may be unnecessary and costly; on the other hand, measuring too infrequently means the patient may forgo needed treatment and experience adverse events related to the disease. We present results from estimating a stochastic model based on longitudinal data for cholesterol in a large cohort of patients seen in the national Veterans Affairs health system. We further use this model to study policies for when to collect measurements to assess the need for cholesterol lowering medications.