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Clin Biochem. 2009 Jan;42(1-2):121-4. doi: 10.1016/j.clinbiochem.2008.10.005. Epub 2008 Oct 25.

A case of hook effect in the serum free light chain assay using the Olympus AU400e.

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University of North Carolina School of Medicine, Department of Pathology and Laboratory Medicine, CB #7525 Chapel Hill, NC 27599-7525, USA.


We describe a case where a woman with an IgG lambda monoclonal gammopathy had an undetectable serum free lambda light chain due to antigen excess. The patient had a three year history of multiple myeloma and initially presented with an elevated serum free lambda light chain. The serum free lambda light chain concentration increased over the course of several months to >4000 mg/L (reference interval 5.7-26.3 mg/L) and then suddenly dropped to <3.0 mg/L. Paradoxically, during this time the monoclonal IgG lambda concentration measured using serum protein electrophoresis increased from 44 to 59 g/dL. Serial dilution of the patient's serum specimen revealed that the serum free lambda light chain was actually 3130 mg/L. This case represents an example of antigen excess or 'hook effect' using the serum free light chain assay.

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