We managed two boys whose carer encouraged us to undertake renal biopsies on them because they had frank haematuria over a prolonged period. However, although routine urine testing did not detect any suspicious findings, near-patient phase-contrast microscopy showed urinary epithelial cells which are not normally present in males, and karyotyping revealed that these cells were female. This was explained by the carer biting her cheek and spitting blood (and buccal epithelial cells) into the urine. Because this method of …