Calcium oxalate monohydrate
Calcium oxalate dehydrate
Calcium hydrogen phosphate dehydrate
Basic calcium phosphate
Magnesium ammonium phosphate
Why Stone Analysis?
Stone analysis is used to evaluate and identify the specific conditions that led to formation of the stone. For example, stones containing calcium likely result from a condition related to calcium metabolism, while a stone containing cystine could suggest cystinuria. The presence of different types of components may be associated with multiple pathogenesis mechanisms. For this reason, stone analysis could be thought of as a “biochemical biopsy” of the urinary tract . Stone analysis may also provide information about the urinary tract environment. A stone containing magnesium ammonium phosphate, for example, points to the presence of a urease-producing bacterial infection of the urinary tract. A new stone occurring in a treated patient can be analyzed to determine the treatment efficacy. A case in which a newly formed calcium phosphate stone is detected in a patient who formerly had a cystine/uric acid stone likely indicates an over-dosage of alkali therapy.
Identification of stone composition may help in choosing future management options. A stone analysis that detected cystine and calcium oxalate monohydrate would contraindicate shockwave lithotripsy (SWL) for the treatment of residual fragments . Detection of drug metabolites such as triamterene, indinavir, and some antacids that lead to stone formation can all lead to treatment modifications to prevent stone recurrence . In addition to other benefits, stone analysis can be used to show epidemiological trends .
Techniques of Stone Analysis
There are two main types of analysis methods: (1) simple wet chemical analysis and (2) more complicated techniques, such as polarized microscopy, X-ray diffraction crystallography, infrared spectroscopy, scanning electron microscopy, and thermogravimetry.
Wet Chemical Analysis
This technique subjects the stone solution to quantitative analysis via the same standard biochemical methods used for analysis of blood and urine. Although it is the most widely used method in routine laboratories, it has several limitations, including the requirement for at least 15 mg of stone material and its tendency to miss rare or unidentified substances. It also has generally poor performance. The efficacy of this method can be improved by using a quantitative wet chemical approach [1, 3].
Optic Polarizing Microscopy
This method uses a polarizing microscope to assess crystals removed from different locations on the stone according to their characteristics (e.g., color and refraction of light) . This method is cost-effective and allows for rapid analysis of small, simple particles. Limitations of the technique include the difficulty of identifying some special cases (e.g., stones containing uric acid, purine derivatives, or calcium phosphate), difficulty in identifying stones with mixed compositions, and the need for specialized training on the part of the analyst [1, 10].