Login to Access Video or Poster Abstract: MP19-06
Sources of Funding: NIH P01 DK56788_x000D_ Japanese-Swedish Research Foundation

Introduction

The mineral in calcium oxalate stones occurs in two forms: calcium oxalate dihydrate (COD) and calcium oxalate monohydrate (COM). The clinical significance of these two forms is not well established, but some studies have suggested that high calcium excretion correlates with the formation of COD stones. Our purpose was to use meta-analysis to evaluate the possibility that in a kidney stone COD may be indicative of hypercalciuria, and to explain why the natural conversion of COD to COM complicates the experimental study of this hypothesis.

Methods

Published reports available in Pubmed or Web of Knowledge were examined for simultaneous determination of COM/COD content in stones and measurements of urine calcium. Examples of urinary stones composed of COD, COM, and COD converting to COM were scanned by micro computed tomographic imaging (micro CT) to examine microscopic structure.

Results

Only 5 studies reported both COD and COM content in stones along with numerical values for urine calcium. Meta-analysis of these studies suggests a strong positive correlation between COD majority content of a stone and high levels of urinary calcium excretion (p<0.001). Additional published studies showed categorical evidence (hypercalciuria versus normal) for the same correlation. Micro CT examination of stones revealed how stones that are formed as COD can convert to COM; this argues for the probable value of assessing stone morphology, in addition to stone composition, as an aid in identifying patients who are likely to have hypercalciuria.

Conclusions

High urinary excretion of calcium correlates with calcium oxalate stones being composed of COD, rather than COM. Such a correlation likely also extends to stones that were formed as COD and converted over time to COM, so the addition of a simple recognition of COD surface crystal morphology to stone analysis would add additional predictive value for hypercalciuria in stone patients.

Funding

NIH P01 DK56788_x000D_ Japanese-Swedish Research Foundation