Kidney stone analysis by FTIR

Morten Moe1, Marianne Moe1, Gunnhild Kravdal1,*

1Unit of Medical Biochemistry, Division of Diagnostics and Technology, Akershus University Hospital, Lorenskog, Norway

Introduction: Kidney stone disease (urolithiasis) is common throughout the world and affects approximately 10% of the population in Europe and the US. Stones that do not pass spontaneously must be removed by surgery or ultrasonic disintegration. To determine the correct composition of the renal stones is imperative to avoid recurrence and may also influence the choice of urologic intervention. Previously the composition has been determined by chemical methods, but this is now considered obsolete, and methods based on X-ray or infrared spectroscopy (IR) are now preferred. Here, we compare a chemical and an IR method for calculi analysis.

Objectives: To determine the composition of calculi fast and reliable.

Methods: Stones removed by surgery were dried and grounded with pestle and mortar, and their composition was determined by a chemical method (DiaSys) and an IR spectrophotometer (Thermo). The IR method was based on attenuated total reflectance (ATR) and the recorded spectra were ATR corrected and compared to spectra in a commercial library to determine the calculi composition.

Results: In general, both methods revealed the building blocks of the calculi (e.g. “phosphate”, “calcium”), however, several calculi minerals may contain phosphate and calcium and only the IR method was capable of reporting the correct mineral composition of the calculi. One stone was composed of a precipitated drug, and only the IR method provided a result regarding its content.

Conclusion: Calculi analysis based on ATR-IR is faster, more reliable, and requires less sample material than the chemical method. The exact mineral composition is determined by IR, and rare drug stones may also be correctly characterized.

Keywords: Biochemistry, Kidney