There have been close to 22 "serious incidents" and two possible deaths linked to the roll-out of non-urgent emergency number NHS 111.
One case involved a patient in the West Midlands who died unexpectedly after calls to the non-urgent care line went unanswered, and poor advice being given.
NHS England announced a review of the model used to roll out NHS 111 late last week, and will “consider if the current model needs revising”.
According to Pulse least 22 possible serious incidents related to NHS 111 have been reported, with of these possible incidents recorded by providers, or commissioners.
Providers or commissioners from 39 of the 43 areas in England that have launched the service provided data.
A spokesperson from Derbyshire Health United - which covers Derbyshire, Nottinghamshire and Northamptonshire - said it was investigating two deaths.
“At this stage of the investigation it has been shown that the system and processes that were followed would have been exactly as expected,” said Lindsey Wallis, chief executive of Derbyshire Health United.
“Sadly the outcome was an unexpected death. DHU reports every death initially as a serious incident until the complete investigation where, following the investigation, there is a determination made as to whether or not it is stepped down from being a serious incident to an incident.”
NHS Direct, which previously ran the phone line for people needing urgent treatment at evenings and weekends, has confirmed that seven potentially serious incidents on the 111 helpline it runs are being investigated.
The incidents occurred between 18 March and 11 April - which included the period when the service was being trialled, it said. During that time, it dealt with about 122,000 calls.
However, the organisation added it was "not unduly concerned" about the level of incidents.
A spokesperson said: "We take the responsibility for the safety and wellbeing of our patients extremely seriously.
"When a concern is raised we listen to the call and undertake an incident review involving experienced clinical staff. This allows us to identify clear actions so that lessons can be learnt and acted on quickly and thoroughly."
An NHS England spokesman said: "The safety of patients must be our paramount concern and NHS England will keep a careful eye on the situation to ensure NHS 111 provides not only a good service for the public, but one which is also safe."
Dr Clare Gerada, chair of the Royal College of General Practitioners (RCGP), said: "The RCGP believes NHS 111 must be more effectively supported if it is going to properly direct patients to the most appropriate form of urgent NHS care.
"It is extremely worrying that there is still so much uncertainty around the delivery and reliability of the advice provided by NHS 111 in some areas.”
A review into NHS 111 has already been announced.