Falsely abnormal serum protein electrophoresis after administration of intravenous immunoglobulins (IVIG): A retrospective cohort study

Intravenous immunoglobulin (IVIG) therapy, used in several neurologic, hematologic, immunologic and dermatologic conditions, is known to interfere with the results of some serum laboratory tests. We analyzed the potential interference of IVIG on serum protein electrophoresis (SPEP) by reviewing more than a decade of SPEP studies performed by the clinical immunology laboratory of the Johns Hopkins Hospital. Of the total 100,350 SPEP performed between January 1, 2013 and December 31, 2023, 395 contained the keyword IVIG in the pathologist report, contributed by 348 patients confirmed to have received IVIG by chart review. Of the 348 patients, 20 (6 %) had a M-spike on SPEP suggestive of monoclonal gammopathy, while 328 (94 %) did not have it. Of the 20 patients, 14 received IVIG within 30 days from the SPEP collection date, while 6 received beyond 30 days. Serum immunofixation electrophoresis (SIFE) and clinical follow up showed no evidence of monoclonal gammopathy in 5 of the 14 patients. Overall, this 11-year retrospective cohort study showed that 5 of 348 (1.4 %) patients treated with IVIG and tested by SPEP had a false M-spike, that is a spike not confirmed to be caused by a monoclonal gammopathy by subsequent studies. Although small, the false positive rate of 1.4 % suggests that integrating knowledge of recent IVIG administration into the pathologist report would reduce SPEP misdiagnosis.