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Approximately 1 - 2% of patients with MM have biclonal gammopathies. When the light chain types differ (as occurs in around half of all biclonal cases), so that the patient has both κ and λ monoclonal sFLCs, κ/λ ratios can be normal [191]. Since it is likely that both FLC concentrations would be elevated, and in different amounts, the clinician would usually be alerted to an abnormality (Figure 7.7) [197]. The issue can be resolved by testing the sample using IFE and identifying two monoclonal bands of different FLC types. Renal function should also be determined to assess the degree of polyclonal elevation of sFLCs that might be attributed to reduced glomerular clearance.

Questions

  1. What is the maximum time that samples for sFLC analysis should be stored at 2-8 ºC?
  2. What should users confirm before moving from one lot of sFLC kit to another?
  3. What causes sample non-linearity?
  4. How can non-linearity be distinguished from antigen excess?

Answers

  1. 21 days (Section 7.1.4)
  2. That internal quality control samples give consistent results with both the new and existing batches of reagent (Section 7.1.5).
  3. Non-specific interference (matrix effects) or the inherent variability of monoclonal FLCs (Section 7.3).
  4. Perform an antigen excess check dilution (in addition to the initial sample dilution, as described in the product insert). If the result obtained at the antigen excess dilution is more than 4-fold greater than the result obtained at the initial sample dilution, the sample should be considered to be in antigen excess (Section 7.4.2).
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