title: Long-term biological variation of serum protein electrophoresis M-spike, urine M-spike, and monoclonal serum free light chain quantification: implications for monitoring monoclonal gammopathies.
abstract: BACKGROUND
  We analyzed serial data in patients with clinically stable monoclonal gammopathy to determine the total variation of serum M-spikes [measured with serum protein electrophoresis (SPEP)], urine M-spikes [measured with urine protein electrophoresis (UPEP)], and monoclonal serum free light chain (FLC) concentrations measured with immunoassay.
  
  
  METHODS
  Patients to be studied were identified by (a) no treatment during the study interval, (b) no change in diagnosis and <5 g/L change in serum M-spike over the course of observation; (c) performance of all 3 tests (SPEP, UPEP, FLC immunoassay) in at least 3 serial samples that were obtained 9 months to 5 years apart; (d) serum M-spike ≥10 g/L, urine M-spike ≥200 mg/24 h, or clonal FLC ≥100 mg/L. The total CV was calculated for each method.
  
  
  RESULTS
  Among the cohort of 158 patients, 90 had measurable serum M-spikes, 25 had urine M-spikes, and 52 had measurable serum FLC abnormalities. The CVs were calculated for serial SPEP M-spikes (8.1%), UPEP M-spikes (35.8%), and serum FLC concentrations (28.4%). Combining these CVs and the interassay analytical CVs, we calculated the biological CV for the serum M-spike (7.8%), urine M-spike (35.5%), and serum FLC concentration (27.8%).
  
  
  CONCLUSIONS
  The variations in urine M-spike and serum FLC measurements during patient monitoring are similar and are larger than those for serum M-spikes. In addition, in this group of stable patients, a measurable serum FLC concentration was available twice as often as a measurable urine M-spike.
authors: Division of Clinical Biochemistry & Immunology, Department of Laboratory Medicine & Pathology, Mayo Clinic, Rochester, MN, USA. katzmann.jerry@mayo.edu
authors: Jerry A
authors: JA
authors: Katzmann
authors: Melissa R
authors: MR
authors: Snyder
authors: S Vincent
authors: SV
authors: Rajkumar
authors: Robert A
authors: RA
authors: Kyle
authors: Terry M
authors: TM
authors: Therneau
authors: Joanne T
authors: JT
authors: Benson
authors: Angela
authors: A
authors: Dispenzieri
mesh_terms: D001797:Blood Protein Electrophoresis; D006801:Humans; D007118:Immunoassay; D007074:Immunoglobulin G / Q000097:blood; D007145:Immunoglobulin kappa-Chains / Q000097:blood*; D007146:Immunoglobulin lambda-Chains / Q000097:blood*; D007136:Immunoglobulins / Q000097:blood* / Q000652:urine*; D008998:Monoclonal Gammopathy of Undetermined Significance / Q000097:blood / Q000652:urine; D009101:Multiple Myeloma / Q000097:blood / Q000652:urine; D009391:Nephelometry and Turbidimetry; D010265:Paraproteinemias / Q000097:blood* / Q000652:urine*; D013997:Time Factors
chemical_list: D007074:Immunoglobulin G; D007145:Immunoglobulin kappa-Chains; D007146:Immunoglobulin lambda-Chains; D007136:Immunoglobulins