PSC: Are IgG and IgG4 the same thing? Do they test different things?

Posted by sandyjr @sandyjr, Apr 1, 2020

My daughter has PSC and the she asked about the IgG4 blood test, she was told that the IgG test had been done. Is this the same thing...did the Dr mean that the IgG test would show anything...I am confused and do not want to push my daughter to further question this if I do not have correct information. Could someone please clarify this? Are these the same test?

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Colleen Young, Connect Director | @colleenyoung | Apr 1, 2020

Hi @sandyjr, I'd like to bring @rosemarya @sandyblair @monty49 @jacinta @jenchavez into this conversation as they have experience living with primary sclerosing cholangitis (PSC) and probably know more first-hand about the relevance of IgG and IgG4 testing.

I'm not a medical professional, but here's some information I found searching studies.

- IgG Subclasses and Allotypes: From Structure to Effector Functions https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4202688/
"Immunoglobulin G (IgG) is one of the most abundant proteins in human serum, accounting for about 10–20% of plasma protein. ... IgG can be further divided in four subclasses, named, in order of decreasing abundance IgG1, IgG2, IgG3, and IgG4."

- The importance of IgG4 screening in patients diagnosed with primary sclerosing cholangitis in the past https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5268050/
In this paper the authors state: While primary sclerosing cholangitis (PSC) has been recognized for decades, immunoglobulin G4-related sclerosing cholangitis (IgG4-SC) has been correctly diagnosed only in recent years. PSC and IgG4-SC show similar clinical symptoms, serologic markers, and imaging results, but the treatment strategies and prognosis of patients differ.

So it seems that IgG4 testing helps to differentiate what type of PSC a patient may have to administer to proper treatments. Has your daughter been tested for IgG4 in the past?

sandyjr | @sandyjr | Apr 1, 2020

I don’t think so. I mentioned to her about the IgG4 and she mentioned it to the doctor and he said that the IgG test had been done and it indicated that she had PSC I believe. So that is why I inquired if there is a difference between the IgG test and the IgG4 test. So she can ask her doctor at this point then if she had the IgG4 test And she can ask for it if she has not. Is that correct.

Rosemary, Volunteer Mentor | @rosemarya | Apr 1, 2020

In reply to @sandyjr "I don’t think so. I mentioned to her about the IgG4 and she mentioned it to..." + (show)

@sandyjr, I don't now about the IgG or IgG4 labs, even though I was I was diagnosed with PSC and later needed a transplant. Your daughter, or any patient can and should ask a doctor when there is a question. Her GI or liver specialist will be able to tell her about the difference in the two tests and whether ot not she needs more testing. He shoud be able to explain it in relation to her particular diagnosis and her particular health background.
Will you or anyone be going with her? When is her next appointment?