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7.4.1. Managing non-linearity

Chapter 7

Binding Site recommend that customers follow the sample dilution protocol shown in each product insert and report the first plausible (non-flagged) result returned by the analyser. Laboratories should also follow their own in-house protocols to ensure that non-linear samples are managed consistently. The use of non-standard sample dilutions, or skipping dilutions should be avoided. Examples of how to report non-linear samples are shown in Tables 7.5 and 7.6.

Dilution Result
(mg/L)
Sample A1/100 95.3
1/2000 202
Dilution Result
(mg/L)
Sample B1/100 145
1/2000 467

Table 7.5. Examples of non-linear κ Freelite results using a Siemens BNII analyser. In this example, the first result was reported (values in bold).

DilutionResult
(mg/L)
Sample A1/10>165
1/100>1650
1/1000790

Table 7.6. Example of non-linear λ Freelite results using a Binding Site SPAPLUS analyser. In this example, as the analyser has generated flags against the results at 1/10 and 1/100 dilutions the first valid result was reported (value in bold).

It is important to note that Freelite results should not be interpreted in isolation and other laboratory findings and clinical symptoms should be considered when evaluating the status of the patient. In addition, IMWG guidelines state that documentation of response requires two consecutive sFLC assessments made at any time, but to confirm response or progressive disease, two discrete samples are required [21][905].