The DAS28 can be calculated using the following formula:
DAS28 = 0.56 * sqrt(tender28) + 0.28 * sqrt(swollen28) + 0.70 * ln(ESR) + 0.014 * GH
This is not a simple formula, but it can easily be calculated using a preprogrammed calculator or other computing devices like our Webcalculator or programmed MS Excel sheet.
When no patient assessment of general health or global disease activity is present a DAS28 with 3 variables, or DAS28(3), can be calculated. The formula is mentioned here, together with all other validated DAS versions.
The DAS28 provides you with a number on a scale from 0 to 10 indicating the current activity of the rheumatoid arthritis of your patient. A DAS28 above 5.1 means high disease activity whereas a DAS28 below 3.2 indicates low disease activity. Remission is achieved by a DAS28 lower than 2.6 (comparable to the ARA remission criteria).
The DAS28 can also be calculated with the CRP instead of the ESR. The C-reactive protein (CRP) may be used as an alternative to ESR in the calculation of the DAS or the DAS28.
There are more formulae to calculate the disease activity, which you can find here.
Using the DAS, several thresholds have been developed for high disease activity, low disease activity or even remission. Also response criteria have been developed based on the DAS, so when the DAS of a patient is measured at two time points (e.g. before the start of a treatment and after 3 months), the patients clinical response can be assessed.