My blood IgG4 level is very high, yet all other tests of organ function are normal. How should I interpret my high blood IgG4 level?
We thank William for this Good Question:
My blood IgG4 level is very high (for example, 700 – 1000 mg/dL in a laboratory in which the upper range value is 86 mg/dL). Yet all other tests of organ function (liver, pancreas, kidney) are normal. How should I interpret this high blood IgG4 level? Should I be concerned?
The serum (i.e., blood) IgG4 level is the best biomarker in the majority of people living with IgG4-RD. (There are exceptions to this, and we will discuss them in forthcoming installments). The higher the serum IgG4 is before treatment starts, the better this blood test tends to be at reflecting the state of disease activity.
But here is a key point:
The direction in which the serum IgG4 level is moving is more important than whether the overall value is elevated or not. Specifically:
If the IgG4 level is lower than it was when measured weeks or months earlier, that is reassuring that the disease is coming under control (or remains under control).
On the other hand, if the level is rising – particularly if there is a substantial jump in the IgG4 level compared to the previous value – then that may indicate that the disease is becoming active again and that re-treatment at some point in the near future should be considered.
The major concern in this scenario is that there might be active IgG4-RD in an organ whose involvement might not be reflected in a routine blood test. For example, routine blood tests can indicate active disease in the pancreas (blood lipase elevation), kidneys (blood creatinine elevation), or liver (alanine or aspartate aminotransferase elevation), but routine blood tests do not detect ongoing disease in the lungs, orbital (eye) region, lymph nodes, aorta, pituitary gland, or retroperitoneum.
A serum IgG4 that is very high, particularly if it is rising consistently, suggests that the disease is active in some organ. Treatment may or may not be necessary, depending on the overall clinical circumstances, but such a patient should be followed carefully. Imaging might be considered to see if a site(s) of active disease can be identified.
In summary, in the scenario raised by William, a careful assessment should be performed by his healthcare provider to ensure that there is no reason to begin (or increase) treatment now.
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