Comparison of infrared and wet chemical analysis of urinary tract calculi

Infrared analysis of urinary tract calculi using the system of interpretation of spectra of Oliver and Sweet [1] was compared with qualitative wet chemical analysis. This method of interpretation could be learned quickly and gave reproducible results, but had some limitations. Advantages of the infrared procedure include greater reproducibility. 1-mg sample size, greater sensitivity for oxalate and more uniform sensitivities. Minimum detectable amounts of reference standards varied roughly within 1 order of magnitude, compared with a range of 10(5) for wet chemical procedures. The comparable sensitivity for oxalate and phosphate permits a semi-quantitative approach for infrared. The main problems relate to the detection of magnesium ammonium phosphate and carbonate apatite, and wet chemical tests are recommended in addition, when these compounds are suggested. Calculi from 308 patients were analyzed by infrared. With this system of interpretation of spectra, infrared is considered to be a major advance in methodology for analysis of urinary tract calculi in the clinical laboratory, compared with qualitative wet chemical procedures.