# Time in remission calculator

Time in remission (TIR) is an alternative outcome measure which covers the entire period of follow-up by estimating an unobserved disease activity based on the available point measurements. The aim is not to perfectly estimate the unobserved disease activity between visits but rather to utilize more efficiently the information contained in two available measurements of disease activity. By definition, the calculation of %TIR requires only two consecutive DAS28-ESR/CRP measurements. By multiplying %TIR using the time between two calendar dates (i.e., the length of the follow-up), we obtain an estimation of the absolute amount of time the patient spent in remission, i.e., the number of months the patient lived in remission during the period between two visits.

### Calculator

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### Results

Time in remission:

Time in remission:

## Time in remission explained

Figure. Time in remission calculated based on the disease activity measured on two consecutive visits

Patient A: The true disease activity (green) remains unobserved between visit X and visit X+1 but it can be approximated with linear interpolation (black line) using disease activity on visit X and visit X+1. Patient A did not achieve remission in either of the two visits and thus his time in remission (TIR) = 0%.

Patient B achieved remission on both visits and hence spent 100 % of his time in remission. This state corresponds to sustained remission.

Patient C did not achieve remission on visit X but did on the following visit. This state corresponds to point remission. TIR in Patient C is high because the patient achieved remission early after visit X.

Patient D, on the other hand, did achieve remission long after visit X. His state would also be rated as point remission, but this patient spent most time with DAS28-ESR above 2.6. Although patients C and D would normally both be categorized as being in point remission, their health states differ importantly. This difference can be captured by the TIR.

The calculator can be cited using the following references:
Tuzil et al. Time in remission as an alternative outcome measure for rheumatoid arthritis: a 10-year prospective study of 2,618 new users of anti-TNF, Rheumatology (Oxford), 2021
Tuzil et al. Time in remission as an alternative outcome measure for ankylosing spondylitis: a 14-year prospective study of 900 users of anti-TNF, ISOPER EUROPE 2022, DOI: 10.13140/RG.2.2.29120.40963

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