Why does the GFR go down in nephritic syndrome?

Q. I have a question. Why do you see a decreased glomerular filtration rate in nephritic syndrome? I read on your blog and other places that it’s due to “hemodynamic changes”– from Robbins I’m assuming this is compensatory stuff- but wouldn’t that increase GFR?

A. It’s because of what’s going on in the glomerulus! In a normal glomerulus, the capillaries are all nice and open and patent. Blood flows through the capillaries like a little river, fluid gets filtered out into the urinary space, and the GFR is normal. But in nephritic syndrome, the glomeruli are stuffed full of cells, and blood flow slows way down.

Take a look at post-streptococcal glomerulonephritis, a common cause of nephritic syndrome. In that disorder, the glomeruli are huge and hypercellular, with tons of neutrophils in there (and probably some other proliferating glomerular cells as well). The poor capillaries are compressed by all that extra stuff, and you can imagine how hard it is for the poor blood to flow through there! If the blood can’t flow through at the same rate, then the filtration of fluid from blood into urine is decreased (and the GFR slows down to a sad little dribble).

Nice water drop: John “K”

What causes nephrotic and nephritic syndrome?


Okay, we talked about how to remember the components of nephrotic syndrome and nephritic syndrome. But what causes these syndromes?

Let’s boil it down to the top causes.

Nephrotic syndrome can be caused by renal diseases or systemic diseases (like diabetes). We’ll just discuss the renal diseases here. All of these diseases are characterized by a loss of foot processes (look it up in a physiology textbook if you’ve forgotten what these are). The three main renal diseases are:

1. Minimal change disease. This is the number one cause of nephrotic syndrome in children. The pathogenesis is unknown. It’s called minimal change (or sometimes “nil”) disease because under light microscopy, the glomeruli look pretty normal! Prognosis is good.

2. Focal segmental glomerulosclerosis. This disorder can be primary, or it may be associated with other conditions (like HIV, or heroin use). It’s called focal segmental glomerulosclerosis because if you look at a kidney biopsy, some (“focal”) glomeruli show partial (“segmental”) hyalinization. The pathogenesis is unknown, and unlike minimal change disease, the prognosis is generally poor.

3. Membranous glomerulonephritis. This type of glomerular disease is really an autoimmune reaction against some unknown renal antigen. Immune complexes are formed and are deposited along the glomerular basement membrane, which appears thickened on light microscopy. If you look at an electron micrograph, you’ll see subepithelial deposits, or “spikes.”

There are two main causes of nephritic syndrome. Both are immunologically mediated, and are characterized by proliferative changes and inflammation in the glomeruli. These causes are:

1. Postinfectious glomerulonephritis. This used to be called post-Streptococcal glomerulonephritis, because it most commonly occurs in children following a case of Strep throat. There’s a rather crude, but useful, mnemonic for this disease: sore throat (Strep infection), face bloat (edema), pee coke (patients often have brown-colored urine). Immune complexes are formed (the antigen is unknown, but probably is some type of Streptococcal protein) and deposited in the glomerular basement membrane (you can see the deposits on electron microscopy; they look like subepithelial humps). On light microscopy, the glomeruli look big and hypercellular, with lots of inflammatory cells. Recovery occurs in most children.

2. IgA nephropathy. This is also called Berger disease. It’s the most common glomerular disease worldwide, and it’s one of the most common causes of recurrent hematuria. It usually occurs in children or young adults, and it presents as hematuria following an upper respiratory infection. Patients with this disease produce abnormally high IgA levels; following an infection, you can see this IgA in the mesangium of the glomerulus (using immunofluorescent stains for IgA). Once IgA gets trapped there, complement is activated, and we all know what that does (bad stuff). The prognosis is variable.

There are, of course, other causes of nephrotic and nephritic syndrome (nothing is ever that easy!). But if you remember the main causes listed above, that should serve you very well.

Note: the photo of coca-cola bottles was taken by DeusXFlorida and can be found at http://www.flickr.com/photos/8363028@N08/3029152878/.