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protein electrophoresis and immunofixation
Serum protein electrophoresis (SPEP): quantitates M component; ⊕ in >80% of Pts Ddx of M component: MM, MGUS (vide supra), CLL, lymphoma, sarcoidosis, RA Polyclonal hypergam seen in inflammatory states: HIV, rheumatic diseases, cirrhosis Urine protein electrophoresis (UPEP): detects Pts who secrete only light chains (= Bence Jones proteins), which are filtered rapidly from the blood Immunofixation: shows component is monoclonal and identifies Ig type → IgG (50%), IgA (20%), IgD (2%), IgM (0.5%), light chain only (20%), nonsecretors (<5%) Serum FLC assay: important for dx (esp. light chain-only Pts) and f/up response to Rx