Clinical and Metabolic Correlates of Pure Stone Subtypes

There are multiple stone types, with each forming under different urinary conditions. We compared clinical and metabolic findings in pure stone formers (SFs) to understand whether there are consistent factors that differentiate these groups in terms of underlying etiology and potential for empiric treatment. Pure SFs based on infrared spectroscopic analysis of stones obtained at our institution between January 2002 and July 2018 with a corresponding 24-hour urinalysis were retrospectively evaluated. One hundred twenty-one apatite (AP), 54 brushite (BRU), 50 calcium oxalate (CaOx) dihydrate, 104 CaOx monohydrate, and 82 uric acid (UA) patients were analyzed. AP, BRU, and CaOx dihydrate patients were younger than CaOx monohydrate and UA patients. The UA patients had the highest male predominance (76.8%), whereas AP patients were predominantly female (80.2%). UA was most associated with diabetes mellitus (45.3%), and CaOx monohydrate with cardiovascular disease (27.2%) and malabsorptive gastrointestinal conditions (19.2%). BRU patients had the highest prevalence of primary hyperparathyroidism (17%). AP, BRU, and CaOx dihydrate patients demonstrated high rates of hypercalciuria (66.1%, 79.6%, 82%). AP and BRU patients had the highest urinary pH. AP patients exhibited the highest rate of hypocitraturia, whereas CaOx dihydrate patients exhibited the lowest (55.4%, 30%). CaOx monohydrate patients had the highest rate of hyperoxaluria (51.9%). UA patients had the lowest urinary pH. There were no observable differences in the rates of hyperuricosuria or hypernatriuria. These results demonstrate that pure stone composition correlates with certain urinary and clinical characteristics. These data can help guide empiric clinical decision making.