Methods for measuring crystallization in urolithiasis research: Why, how and when?

Whereas crystalluria does not distinguish between kidney stone formers and healthy people and thus can be considered a physiologic event, kidney stone formation is a pathologic incident and reflects a specific form of biomine ralization. Both single urinary crystals as well as whole kidney stones for m under exquisite control of organic macromolecules. Simple crystal formati on in the urinary tract is distinguished from stone formation in the kidney by the process of particle retention. The latter occurs either because nuc leated crystals strongly aggregate to particles too large to pass freely th rough the tubules ('free particle' theory), or because crystals become abno rmally adherent to tubular cell surfaces ('fixed particle' theory). Since i t is impossible to mimic all the processes involved in stone formation in v itro, it is highly important to carefully chose a specific crystallization process for in vitro studies, and to select the most appropriate experiment al conditions for measuring the chosen process as reliably as possible. Thi s overview aims at critically reviewing the principles of currently availab le assay systems for studying crystallization processes involved in stone f ormation. Consensus is reached by the experts that no in vitro system reall y mimics what happens in renal stone formation, but that carefully designed in vitro studies will always play an important part in urolithiasis resear ch. For such studies, it is highly important to exactly control the appropr iate experimental conditions that are relevant to a specific crystallizatio n process under investigation. Practical guidelines for researchers working with crystallization systems are provided, and it is concluded that intern ational efforts should be made to standardize the terminology, to agree on a set of basic experimental parameters (temperature, pH, artificial urine c omposition), and to adopt simple tests or conditions are reference points f or quality and comparative control. Copyright (C) 2000 S. Karger AG, Basel.