A woman who was being tested for Covid-19 in hospital ended up having the swab snap off into one of her lungs, a report said.
The patient, in her 50s, had a tracheostomy, a procedure where an opening in the neck is made.
When a nurse tried to swab the woman for Covid-19 through her neck tube, the swab snapped off into her right lung.
The trust in Leicester, where the woman was being treated, said additional safety measures were now in place.
The patient was being treated by University Hospitals of Leicester NHS Trust after a neurosurgical operation, a British Medical Journal (BMJ) report said, and was due to be discharged to a nursing home.
The test swab is designed to snap to fit into its test tube.
As the tracheostomy had bypassed her mouth, medical staff decided to swab through the tracheostomy tube, during which "the nurse felt the swab stylet snap".
The swab ended up in the woman's lung and doctors had to remove it using a flexible bronchoscopy.
The report said: "There is a need for clear guidance on how to test patients with front of neck airways."
A trust spokesman said it had put in place "additional safety measures" and shared "learning" with staff following the case.