Differentiation between SLE activity and infection

Dr Christian Dejaco is an associate professor in the Department of Rheumatology at the Medical University of Graz (Austria) and author of the European League Against Rheumatism (EULAR) recommendations for the management of polymyalgia rheumatica and large vessel vasculitis.

How can we differentiate between a flare of systemic lupus erythematosus (SLE) and an infection?

Christian Dejaco, MD, PhD: [So to be] more specific: How can we differentiate in lupus between an infection and the activity of the disease? It is not a single lab parameter. What we should do is a combination of history, clinical examination, and lab exams.

One particularity of lupus is that patients with the activity of lupus usually have a very high erythrocyte sedimentation rate (ESR), whereas an elevation of C-reactive protein (CRP) is usually indicative of an infection. When we have a rise of ESR with a low CRP, it is more probable that it is the activity of lupus and, vice versa, when we have a very high CRP with only moderately elevated ESR, then it is more probable that the patient is suffering from an infection.

The complement [measurements] help as well. Many have a consumption of complements that may indicate an activity of lupus.