Hello Sir. Assessing expression of CD64 on neutrophils (inducible during infection, vs constitutive expression on monocytes and macrophages) by flow cytometry seems to hold much promise and was presented as an oral paper at the ACR in 2016 in a work from Prof Vikas Agarwal's group. Regards,

 Durga

http://acrabstracts.org/abstract/utility-of-neutrophil-cd64-expression-strem-1-in-distinguishing-bacterial-infection-from-disease-flare-in-sle-and-anca-associated-vasculitis/

Dear Durga,

Thanks, I had seen this abstract. I just thought of generating some discussion on this topic in this forum

Best wishes,

Aman

Dear Dr Sharma,

Biased by my own research I suggest we should attempt to get our finger around neutrophil extracellular traps. Here is a link to our research presented at ACR 2016:

http://acrabstracts.org/abstract/net-inducing-capacity-is-a-biomarker-in-anca-associated-vasculitis-independent-of-anca-antibodies/

best wishes

Onno

http://acrabstracts.org/abstract/net-inducing-capacity-is-a-biomarker-in-anca-associated-vasculitis-independent-of-anca-antibodies/

In addition to previos answers, Procalcitonin is useful.

Amongst the investigations which most people have access to (excluding things like flow cytometry), I have found CRP (in flare of lupus, high ESR with normal / mild increase in CRP as against proportionate increase in infection), low complement, high titres of ds DNA and organ specific markers (proteinuria, restrictive lung function, signs on neuroimaging etc) useful in differentiating a flare from infection. Thanks.

I also have simillar experience as Dr Warrier. Both ESR and CRP are raised in both scenarios but a disproportionately high CRP on a background of Neutrophilia and clinically toxic look of the patient favour infection more than the dusease flare.