Metabolic investigation of stone formers Abstract. Once a kidney stone has passed, patients must be carefully evaluated in order to identify the underlying cause of the disease and to guide preventive measures and treatment. General recommendations can be offered to all kidney stone formers, but personalized counseling and follow-up adaptations need to be guided by in-depth assessment. Metabolic evaluation for recurrent stone formers is based on 24 h urine collection. This allows a comprehensive understanding of the dietary habits of the patient and helps identifying treatable metabolic diseases and renal tubulopathies. Additional specific assessments may include urine acidification test (in case of suspected partial renal distal tubular acidosis), characterization of hypercalciuria or osteodensitometry. Metabolic evaluation often needs to be repeated over time to guide therapeutic interventions, both dietetic and drug-related.