Increased detection rate of melamine-containing calcium urolithiasis by using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry technique in clinical practice

• Melamine content in calcium stone specimens was analyzed by FTIR and MALDI.
• Melamine detection limit by MALDI was a ~ 10,000-fold more sensitive than FTIR.
• MALDI can increase melamine detection rate in stones not detectable by FTIR.
• Melamine content can be detected in clinical stone specimens.
• MALDI can be an additional tool to evaluate external exposure of melamine.

BackgroundStudies have shown that melamine may be associated with urolithiasis. A more sensitive method is needed to analyze melamine in urinary stones to identify potential causes of urolithiasis.MethodsHere we compare the analytical methods of detecting melamine in urinary stones by Fourier transform infrared (FTIR) spectrophotometer and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) in the laboratory and clinic. First, we established the melamine detection limit in melamine-cyanurate standard by the methods of FTIR spectrophotometer and MALDI-TOF MS. Subsequently, we applied these methods to 54 adult patients with upper urinary tract calcium urolithiasis.ResultsThe detection limit of melamine in melamine cyanurate standard by MALDI-TOF MS was ~ 10,000-fold more sensitive than FTIR. We applied both instruments to 54 stone specimens from 54 calcium urolithiasis patients. In those without distinctive melamine pattern in the FTIR spectra, melamine could be detected by MALDI-TOF MS in an additional 12 out of 42 subjects' stone specimens (28.6%). Compared to MALDI-TOF MS-negative subjects (n = 30), those positive subjects (n = 12) excreted significantly higher urinary melamine levels (P < 0.05).ConclusionsCompared to FTIR, MALDI-TOF MS is a more sensitive method to detect the content of melamine in melamine-containing kidney stones.