Cdai Score Calculator

The Clinical Disease Activity Index is deliberately the least mathematical of the rheumatoid arthritis composite scores: it is the plain sum of four numbers, with no square roots, logarithms, or weighting coefficients. Tender joint count and swollen joint count are each assessed across the same 28 joints used by DAS28, namely the shoulders, elbows, wrists, metacarpophalangeal joints, proximal interphalangeal joints, and knees. To these are added the patient global assessment and the evaluator or physician global assessment, each recorded on a 0 to 10 cm visual analog scale. The theoretical range is 0 to 76, although scores above 40 are rare in practice. Because joint counts and global scores enter unweighted, a single point of the total means the same thing wherever it comes from, which makes the index unusually easy to interpret and to explain to a patient. Validated cut-offs are 2.8 or less for remission, above 2.8 to 10 for low activity, above 10 to 22 for moderate, and above 22 for high. These were calibrated against rheumatologists actual treatment decisions rather than derived from a statistical distribution. CDAI remission is stricter than DAS28-ESR remission below 2.6, which can be reached with several joints still swollen. The trade-offs are real: the 28-joint count excludes the feet and ankles, both global assessments are subjective and are inflated by concurrent fibromyalgia, depression, or osteoarthritis, and omitting an acute phase reactant means subclinical inflammation visible on ultrasound or reflected in CRP goes unrecorded.

Composite scoring in rheumatoid arthritis began in Nijmegen in the Netherlands, where the original Disease Activity Score was constructed around 1990 by regressing rheumatologists decisions to change treatment onto clinical variables, and was reduced to 28 joints by Prevoo and colleagues in 1995. The resulting DAS28 formula required a calculator and a laboratory result, which limited its use during the visit itself. Josef Smolen, Daniel Aletaha, and colleagues in Vienna addressed both problems. They introduced the Simplified Disease Activity Index in 2003 as a straight sum of the two joint counts, the two global assessments, and CRP in mg/dL, showing that a linear untransformed index performed as well as the transformed one. In 2005, in Arthritis Research and Therapy, Aletaha and Smolen went further and reported that acute phase reactants added little to composite indices once joint counts and global assessments were included. Removing CRP from SDAI produced the CDAI, an index that needs no blood test at all and can therefore be completed before the patient leaves the room. That property made it well suited to the treat-to-target strategy formalised in the 2010 international recommendations, which call for reassessment and treatment adjustment at intervals of one to three months in active disease. The 2011 ACR and EULAR remission criteria formally recognised a CDAI of 2.8 or less alongside the stricter Boolean definition.