The first observation of calcium oxalate accumulation in human hair

Oxalate metabolism is an important process for multiple health conditions such as primary and secondary hyperoxaluria, urolithiases, and crystalline nephropathies. Here, we report for the first time, the detection of calcium oxalate in the medulla of human hairs from the general population. Using synchrotron FTIR microspectroscopy calcium oxalate was found in 11% of the hairs. Calcium oxalate was most frequently observed within or contiguous to the hair medulla and was detected in the cortex in only one hair. Calcium oxalate was identified in its monohydrate form (COM). The origin of COM in hairs from the general population sample is currently unknown but its frequency could be compatible with different origins: secondary hyperoxaluria, or hair treatments. These results suggest that the use of calcium oxalate in hair as a non-invasive biomarker could present several promising clinical applications in the management and monitoring of conditions related to oxalate metabolism such as kidney stone formation, and primary oxaluria.