Vital tests to track the progress of rheumatoid arthritis are not being given to thousands of sufferers, it has been claimed.
A tenth of patients questioned said they have never had their disease activity score (DAS) measured.
DAS assesses the progress of rheumatoid arthritis (RA) and monitors how well the disease is being controlled, and is seen as crucial to help doctors make decisions about treatment.
A DAS assessment should be carried out at least every six months, according to the National Institute for Health and Clinical Excellence (NICE).
It is estimated that around 487,000 people in the UK suffer from RA. It costs between £3.8bn and £4.75bn a year to treat the an auto-immune disease that attacks the joints and causes long-term disability.
Results of a survey by the charity released at the British Society of Rheumatology's annual meeting in Glasgow suggest that 90% of RA sufferers do not know their DAS score.
Professor Peter Taylor, from Imperial College London said: "Rheumatoid arthritis can often be well controlled by treatment, and much research shows that this is best achieved when a regular measurement of disease activity is undertaken in order that appropriate adjustments to treatment are made.