Chapter Three · C3 glomerulopathy
One of the things people type into Google most is foam in my urine, should I be worried
.
Sometimes it is nothing. Sometimes it is protein leaving through a kidney that is letting it through. This chapter is about telling which, and what to ask for.
A word from the immune system, on a kidney report, with no plain explanation attached.
Start with a phone call. Your doctor’s office has a triage line and a nurse will talk it through with you. They are good at this, they do it all day, and it costs nothing. You ring the main number and ask for the triage nurse. There is no charge and you do not need an appointment.
If it feels more serious than that, go to urgent care. You will usually be seen faster than at a hospital.
If it feels life-threatening — chest pain, trouble breathing, confusion, no urine at all for a day — call 911 or go to the emergency room. Do not wait until you are sure. Take the more cautious road.
Rather listen?
Takes about 7 minutes, read aloud. It is the same words as the page below, so nothing is missing if you would rather read. Download it to keep on your phone — it will play with no signal, in a waiting room or a car.
Complement is part of the immune system that idles in the background. In C3
glomerulopathy it does not switch off properly, and the leftovers build up in the
kidney’s filters.
→ where this is explained: What complement is, in plain terms
“C3” on the report is the name of the deposit, not the cause of it.
It says what was found in the tissue. The next question is what set it off.
→ where this is explained: What sets it off
In adults, especially after fifty, the trigger is often an abnormal blood
protein — and that connection is regularly not followed up.
→ where this is explained: If this began after fifty
Tick the ones that apply. The bar below shows how much they add up to.
What we would do, as a friend rather than as your doctor. This is our opinion and we stand behind it. It is not medical advice and we are not examining you.
It is not a one-time reading. If you start feeling worse while you are deciding, move up a level. Nobody has ever been criticised for turning up and being sent home. A false alarm is the best possible outcome here.
If none of these apply, the rest of this chapter is worth your time. Take it slowly; there is no clock on it.
Complement is a set of proteins in the blood that acts as an alarm and clean-up system. One branch of it — the alternative pathway — is always ticking over in the background, ready. It is meant to be held in check by regulators that switch it off again.
In C3 glomerulopathy that control fails. The pathway runs on, and fragments of the C3 protein accumulate in the filtering units of the kidney. The biopsy sees them, which is where the name comes from.
The control can fail for more than one reason, and they matter because they point to different treatments.
An inherited difference in one of the regulator proteins. More common in children and younger adults.
An antibody that gets in the way — the best known is one that stabilises the switch in the “on” position, so the pathway cannot shut down.
An abnormal monoclonal protein made by a small clone of plasma cells, which interferes with the same regulation. This is the one that connects to the MGRS room.
Grade B In adults, and particularly over fifty, a substantial share of C3 glomerulopathy is driven by a monoclonal protein. The practical consequence is direct: finding C3G in an older adult is itself a reason to look for that protein, with the blood and urine tests set out in the MGRS room.
That look is often not made, because the kidney finding is treated as the whole answer. It is worth asking whether it was.
Blood complement levels — C3 in particular, sometimes low — are usually followed, along with more specialised tests of the pathway.
Grade A One caution about those specialised tests, from the laboratories’ own quality programmes: for several complement measurements there is no agreed reference method and no target value, and different laboratories report in different units. Two results from two hospitals may not be comparable even when the test has the same name. If your numbers were taken at different places, that is a fair thing to raise.
“What does the biopsy report say was actually deposited, and in what pattern?”
“Have we looked for a cause — an inherited difference, an antibody, or a monoclonal protein?”
“Given my age, has a serum free light chain assay been done?”
“My complement results come from more than one laboratory. Are they measured the same way?”
A free app called Insight Kidney walks through the kidney from the whole organ down to a single filter, and shows what C3 deposits do to a single filter. It is the clearest picture of this we have found, and some people take in a shape far faster than a paragraph.
It is made by Anima Res, a German medical animation studio, and it was paid for by Novartis, who sell drugs for some of these conditions. We have no connection to either one. We link it because the anatomy is good, and we name who paid so you can weigh that yourself.
It is a phone app, and it opens outside this book. App Store · Google Play · what it is
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Written from the general clinical and laboratory-quality literature. Nothing on this page comes from any individual’s medical record. Statements resting on evidence that is established rather than universal carry a grade.