Can sIL2-R differentiate between active sarcoidosis affecting small airways vs uncontrolled asthma and guide treatment with methotrexte vs biologics?

This is an interesting question. Just to provide a little context, I used to have a sarcoidosis-focused clinic where one day each week I would see only sarcoidosis patients. I also had a day of seeing only neurosarcoidosis patients once per month, together with neuroimmunology.

To be honest, since I have seen it commonly be elevated in mimics including lupus, multiple sclerosis, and lymphoma, I've actually stopped using soluble IL-2 receptor in my practice. I know there is a large body of literature out there to support it, but in my patient population, the usefulness has been less exciting than what I had otherwise been led to believe.

Not exactly, and probably not with enough compelling precision to use it clinically. sIL-2R cannot reliably differentiate active small-airway sarcoidosis from uncontrolled asthma, nor can it independently select methotrexate versus biologic therapy. It is a marker of systemic T-lymphocyte/granuloma activation that helps support a diagnosis of sarcoidosis versus non-granulomatous conditions, and can track disease activity during treatment, but it is neither lung-specific nor validated as a treatment-selection tool.