How to assess disease activity in ankylosing spondylitis? Some people still believe that CRP or ESR are good tools for measuring disease activity in ankylosing spondylitis.
The BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) is a standard tool for measuring and evaluating disease activity in ankylosing spondylitis. The BASDAI is easy to score by patients (fatigue, spinal pain, joint pain/swelling, localized tenderness, morning stiffness duration, morning stiffness severity) and easy to calculate by physicians/health personal. So one should have it at each visit. The patient can even take one home and fill it out, say a week after an infliximab infusion to monitor the therapeutic effect.
The new kid on the block is the ASDAS (Ankylosing Spondylitis Disease Activity Score). The ASDAS is a composite index to assess disease activity in ankylosing spondylitis. The authors of the original text favour the ASDAS-CRP, which takes into calculation: back pain, duration of morning stiffness, patient global, peripheral pain/swelling, and CRP. Most of the data you already have in the BASDAI, you have to ask the patient global ("How active was your spondylitis on average during the last week?") and take blood for CRP. For the ASDAS-ESR you have to take blood for ESR. The formulas to calculate the ASDAS can be easily put into a spreadsheet. Just takes seconds to put in the data and calculate the ASDAS.
How to use the ASDAS? What can you do with the results? If the ASDAS is lower than 1.3 it’s (hooray) inactive disease, 1.3 to lower 2.1 means moderate disease activity, 2.1 to 3.5 means high disease activity, above 3.5 is defined as very high disease activity. A difference of above 1.1 means a clinically important improvement and above 2.0 is defined as a major improvement.
Let’s hope that the ASDAS finds its way into daily practice!
ASDAS-CRP: 0.12 x Back Pain + 0.06 x Duration of Morning Stiffness + 0.11 x Patient Global + 0.07 x Peripheral Pain/Swelling + 0.58 x Ln(CRP+1)
ASDAS-ESR: 0.08 x Back Pain + 0.07 x Duration of Morning Stiffness + 0.11 x Patient Global + 0.09 x Peripheral Pain/Swelling + 0.29 x √(ESR)
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