Jonathan Barratt, PhD, FRCP: And what is the role of electron microscopy? We routinely do EM on all our kidney biopsies, but what would you be looking for in an electron microscopy?

Sanjeev Sethi, MD: That's a great question. Whether EM is required or not. This is the same at the Mayo Clinic, and most academic centers in the US and Europe probably do electron microscopy. It's more of a confirmation than anything else. So, in case of IgA nephropathy, this is characterized by mesangial electron-dense deposits. So, when you do the EM, you confirm the diagnosis of IgA nephropathy. If you ask me, do you really need EM for IgA nephropathy? Probably not. You can get away with it. There is a certain differential diagnosis of IgA nephropathy, since we're talking about it, that one needs to keep in mind. When you see IgA nephropathy on immunofluorescence microscopy, remember IgA nephropathy is a diagnosis where the deposits are primarily mesangial. But if you start seeing deposits along the capillary walls, there's bright C3, and you do electron microscopy in these cases and you find a few subepithelial humps, that means the deposits are not all sitting in the mesangium, you start thinking of an infection related IgA, dominant, it's a long name. Infection-related IgA-dominant glomerulonephritis. These are very often patients who had a staph infection. Very often these patients are diabetic. The other place where EM is useful, sometimes when you see IgA and occasionally, you might see some IgG with it. You must worry about lupus, autoimmune disease as well, so then electron microscopy becomes helpful there as well. There are certain pointers that you get towards an autoimmune disease. Although most IgAs are relatively easy to diagnose, you can see IgA on immunofluorescence and other diseases, one is infection related GN, the other one is in autoimmune disease particularly lupus, IgA vasculitis or Henoch-Schonlein purpura is sometimes indistinguishable from IgA nephropathy on the biopsy.

Jonathan Barratt, PhD, FRCP: Thanks, and there's a lot of interest in complement therapies and you mentioned that C1Q is almost always negative.

Sanjeev Sethi, MD: Typically, negative.

Jonathan Barratt, PhD, FRCP: What does that signify if there's C3 present but C1Q is absent?

Sanjeev Sethi, MD: Typically C1Q is negative on the immunofluorescence microscopy and IgA nephropathy, on the other hand C3 is extremely bright. When you see absence of C1Q and you see bright C3 you think of two things, it's either coming through the alternative pathway because you're skipping the C1Q or it's coming through the lectin pathway because again that's skipping the C1Q. Most labs don't do what's a stain called C4 or a sort of byproduct of C4, a pathway, it's called C4D. If you can do a C4D, very often some of these patients with IgA nephropathy will show you the IgA. They'll also show you the C3 but they also show you the C4. When you see bright C4 in addition to the C3 and the absence of C1Q you sort of think that this is coming out into the lectin pathway. There are studies that have shown that IgA nephropathy, probably the lectin pathway of complement, also plays a role in these patients.

Jonathan Barratt, PhD, FRCP: That's probably going to become more and more important, isn't it in terms of how we decide when these new therapies become available which approach we might want to take.

Transcript Edited for Clarity