PTH and rectal cancer: Here, we report a case of falsely elevated parathyroid hormone (PTH) due to immunoassay interference and review the literature.<h4>Case presentation</h4>A 57-year-old man who recovered well from lung metastasis of rectal cancer treated with bevacizumab and sintilimab for 1 year, presented to Peking University People's Hospital with persistently high PTH levels (>1200 ng/L) measured by a Roche Elecsys assay.