More than 170 islanders, prescribed biologic medication for rheumatology conditions, did not meet the criteria to start the therapy.
Health and Community Services' recent audit also found a lack of evidence to confirm the accuracy of first diagnoses for three in ten patients.
Health Minister, Deputy Karen Wilson, says initial findings from this audit highlight some serious problems in the rheumatology service.
"It is clear these underlying issues may extend into other parts of HCS.
As I have said previously – and as this audit indicates – we have fallen behind “best practice” in a number of areas, and we now need to redouble our efforts to strengthen clinical governance and quality of care within HCS."
Biologics are immunosuppressant drugs, used to treat several conditions, such as arthritis, cancer and Crohn's Disease.
However, this does not necessarily mean the diagnosis was incorrect, as some accurately pinpointed rheumatology conditions.
All patients involved in the audit have met with specialist rheumatology professionals, and their care and treatment are being reviewed.
Patrick Armstrong, Medical Director at HCS, says the diagnosis and treatment of the broader group of rheumatology patients will be reviewed as quickly as possible.
"HCS will be starting this further review immediately, and if there is a need for any patient to be seen in person, they will be contacted directly.
In the meantime, patients should continue to take their medication as prescribed and attend their hospital and doctor appointments as normal."
The RCP's final report, commissioned by HCS last year when questions were raised about clinical record keeping, is expected in the autumn of this year.
Its initial findings show that, at the time, notes were poorly written, biologic agents were inappropriately prescribed and prescriptions did not include the clinical condition being treated.
The Chair of Jersey Arthritis Society, Maureen Parris, says patients will understandably be concerned about these audit findings.
"It is reassuring that their care and treatment has been reviewed and more reassuring to note that Jersey’s rheumatology service is now being run by a specialist Consultant Rheumatologist on the General Medical Council’s Specialist Rheumatology Register."