I was wondering if anyone has ever heard of a positive monoclonal protein showing up in laboratory tests being connected to a monoclonal antibody drug, specifically Benlysta (belimumab), which is used to treat lupus.
I have a positive monoclonal IgG lambda protein showing up on one of my laboratory tests, and I am being treated with Benlysta, so I'm just wondering if the Benlysta could be causing a "false positive" test. I also have an abnormally low kappa-lambda free light chain ratio and have hypogammaglobulinemia. It looks like I'm going to have a bone marrow biopsy, and before that happens, I thought I'd check on this.
Thanks!
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Re: Benlysta and multiple myeloma-related lab tests
Dear AustinLisa,
Great question. As it turns out, Benlysta (belimumab) is an IgG lambda monoclonal antibody. As such, it is possible that your "M spike" is the Benlysta causing a false positive. We have seen this with other therapeutic monoclonal antibodies.
In our experience, when patients have "M spikes" due to the use of therapeutic antibodies, the M spike level tends to be quite low. It might be detectable on serum protein electrophoresis (SPEP) and immunofixation, but is difficult to quantify.
I am not aware of therapeutic antibodies affecting the serum free light chain testing. They should not cause hypogammaglobulinemia UNLESS the function of the antibody is to suppress B cells (which is what Benlysta does). If the M-spike is trace detectable, and the free light chain level only minimally abnormal, you may want to bring this to the attention of your hematologist-oncologist and discuss whether they feel the Benlysta could be causing the laboratory abnormalities you are seeing.
Let us know how things go and good luck!
Pete V.
Great question. As it turns out, Benlysta (belimumab) is an IgG lambda monoclonal antibody. As such, it is possible that your "M spike" is the Benlysta causing a false positive. We have seen this with other therapeutic monoclonal antibodies.
In our experience, when patients have "M spikes" due to the use of therapeutic antibodies, the M spike level tends to be quite low. It might be detectable on serum protein electrophoresis (SPEP) and immunofixation, but is difficult to quantify.
I am not aware of therapeutic antibodies affecting the serum free light chain testing. They should not cause hypogammaglobulinemia UNLESS the function of the antibody is to suppress B cells (which is what Benlysta does). If the M-spike is trace detectable, and the free light chain level only minimally abnormal, you may want to bring this to the attention of your hematologist-oncologist and discuss whether they feel the Benlysta could be causing the laboratory abnormalities you are seeing.
Let us know how things go and good luck!
Pete V.
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Dr. Peter Voorhees - Name: Peter Voorhees, M.D.
Beacon Medical Advisor
Re: Benlysta and multiple myeloma-related lab tests
AustinLisa,
Did you ever get any answers from your doctors? I was randomly searching to see if anyone else on Benlysta had tested with a monoclonal gammopathy protein. I have the same test results! It was found in April, retested in August. I saw my doctor a few weeks ago and he said the August test still shows the same results. I am being referred to a hematologist for further testing. I have been on Benlysta since July 2011. I am trying to figure out if this protein is a false positive. I also know Benlysta can make me more prone to cancer, but I have not been able to find out what kind.
Dr. Voorhees, I appreciate your take on this and the information you provided.
I would love any input! I see the hematologist December 19, 2013.
Bren Ramsey
Diagnosed with SLE 2004
Fibromyalgia 2013
Polymorphous Light Eruption 2013
Monoclonal Gammopathy 2013
Did you ever get any answers from your doctors? I was randomly searching to see if anyone else on Benlysta had tested with a monoclonal gammopathy protein. I have the same test results! It was found in April, retested in August. I saw my doctor a few weeks ago and he said the August test still shows the same results. I am being referred to a hematologist for further testing. I have been on Benlysta since July 2011. I am trying to figure out if this protein is a false positive. I also know Benlysta can make me more prone to cancer, but I have not been able to find out what kind.
Dr. Voorhees, I appreciate your take on this and the information you provided.
I would love any input! I see the hematologist December 19, 2013.
Bren Ramsey
Diagnosed with SLE 2004
Fibromyalgia 2013
Polymorphous Light Eruption 2013
Monoclonal Gammopathy 2013
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