For this calculator, we obtained data from the Leiden Early Arthritis Recognition Clinic (EARC) at the Leiden University Medical Centre. The EARC is a screening clinic where rheumatologists perform joint examination on synovitis in patients in whom GPs were unsure about the presence of inflammatory arthritis. Using multivariable regression modelling we derived a simplified rule consisting of 7 items, as shown in the calculator. The AUC was 0.74 (95%C.I. 0.70–0.78). The model was validated in a dataset of 644 other patients. Here the AUC was 0.71 (95%C.I. 0.67–0.75).
In both datasets of patients with suspected inflammatory arthritis (according to their GPs), inflammatory arthritis was confirmed by the rheumatologist in 41%. Data obtained in some other GP practices suggested that the pre-test risk on the presence of confirmed inflammatory arthritis in suspected patient is approximately 20%. Therefore the calculator can also estimate the risk on inflammatory arthritis in this setting.
Any healthcare professional who doubts if a patient has inflammatory arthritis can use the calculator by entering their patient's characteristics. It will yield a risk score that corresponds to a probability of current inflammatory arthritis. This information might assist in the decision making process: healthcare professionals may decide to refer to rheumatology care, order additional investigations, or (in case of a low risk) apply a wait-and-see approach.
This prediction model and calculator can aid in discrimination of patients with inflammatory arthritis. It cannot replace physical examination by an experienced rheumatologist. The authors are not responsible or liable in any manner for the use of this calculator. By using this calculator, the user agrees to exclude the authors of this calculator of any liability as well as excluding the Leiden University, Leiden University Medical Centre, and Keele University of any liability directly or indirectly following the use of this calculator. If the user of this calculator applies the calculator to the benefit of third parties, the user indemnifies the Leiden University, Leiden University Medical Centre, Keele University, and the authors of this calculator, as well for any claims of third parties based on the use of this calculator.