A Thames Valley police spokesman said the actions of Constable Karen Fry were to be commended for resolving the incident at the Churchill Hospital in Oxford without injury to any person.
Armed police were called to the hospital shortly after 9am on Thursday morning after a patient snatched the syringe from a doctor and plunged it into his arm, partly filling it with his blood. He then grabbed a knife from the hospital kitchen and ran through wards, threatening to kill staff.
Police were alerted that a man was "going berserk" and an armed response unit with protective clothing was called. Escape routes at the hospital were sealed off.
But PC Fry, 30, succeeded in establishing a rapport with the patient who began to respond to her appeals for calm.
After around 15 minutes, the police officer persuaded him to hand over the syringe and the knife without further incident.
It is not thought likely that the man, who was in the infectious diseases unit, will face any charges.
The Thames Valley police spokesman said it had been believed that there was a real risk at the hospital which was averted by the prompt actions of the officers and, in particular, by PC Fry.
Officials at the hospital are understood to be reviewing its security measures in the light of the incident.
PC Fry was later quoted as saying: "It is just a job. I was not scared at the time, but afterwards my heart was pounding, especially when I thought about the nine-inch knife and the syringe and what could have happened."Reuse content