A new study has revealed that recent administration of intravenous immunoglobulin (IVIG) can lead to false positive results in serum protein electrophoresis (SPEP) testing, potentially causing diagnostic confusion and unnecessary medical procedures.
Impact on Laboratory Testing Accuracy
The retrospective cohort study examined 100,350 SPEP tests, focusing on 395 cases that mentioned IVIG in the pathologist report. Among 348 confirmed IVIG recipients, researchers identified a 1.4% false positive rate for monoclonal gammopathy, representing five patients who showed M-spikes that were not confirmed by subsequent diagnostic assessments.
IVIG, derived from plasma pooled from thousands of donors, has been previously known to affect various laboratory tests that measure serum antibodies. This interference is significant enough that IVIG manufacturers include specific warnings about potential testing interference in their product information.
Clinical Implications and Detection Patterns
The study found that 20 patients (6%) demonstrated abnormal SPEP results based on the presence of specific markers including spikes, bands, monoclonal proteins, or gammopathy indicators. Notably, 14 of these cases occurred within 30 days of IVIG administration, establishing a clear temporal relationship between treatment and false results.
Diagnostic Reliability and Healthcare Impact
SPEP combined with serum immunofixation electrophoresis (SIFE) typically provides highly reliable results in diagnosing monoclonal gammopathies, with a sensitivity of 92.7% and specificity of 96.3%. While the false positive rate attributed to IVIG is relatively small, its impact on diagnostic accuracy cannot be ignored, particularly in conditions such as multiple myeloma where precise testing is crucial.
Recommendations for Healthcare Providers
The research team emphasizes the importance of maintaining detailed records of IVIG administration and implementing clear notification systems in patient charts. Healthcare providers, including physicians and pharmacists, are advised to:
- Consider recent IVIG treatment when interpreting SPEP results
- Plan serum tests around IVIG therapy schedules when possible
- Exercise caution when ordering SPEP without complete patient history
- Implement clear notification systems for IVIG administration
These measures aim to prevent misdiagnosis and avoid unnecessary, expensive diagnostic workups that might result from false positive results.
