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Approximately 1 - 2% of patients with MM have two monoclonal proteins with distinct heavy and/or light chain types (e.g. IgGk and IgAk), termed biclonal gammopathy (Section 17.1) [1041][355]. The light chain types differ between the dominant and minor clones in around three quarters of cases [1041]. In most patients, an increase in κ or λ sFLC concentration is observed and is mediated by the dominant clone, leading to an abnormal sFLC ratio. However, in a small proportion of biclonal patients, an abnormal sFLC ratio results from the minor clone producing monoclonal sFLCs, and in a few patients κ/λ sFLC ratios are normal (Figure 7.8.) [1041].

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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