On 4 March, South West London Pathology (SWLP) identified an issue with Faecal Immunochemical Test (FIT) test results from between 27 December 2025 to 4 March 2026. During this period, some results were issued that were falsely high (positive). All results that went out from 5 March onwards are correct. The FIT test looks for […]
Serum Free Light Chains
| Category | Immunology and PRU |
|---|---|
| Turnaround time | Weekly |
Additional information
Purpose of test
Investigation of suspected B cell malignancy, eg myeloma, lymphoma.
Prognosis and monitoring of patients with myeloma.
Sample type
Serum
Sample volume
300ul
Change of method
From 23 December 2025, serum free light chains will be measured using the N latex method. This is to allow more efficient sample processing as serum free light chains and immunoglobulins will be measured on the same analyser.
The test name has been updated to include the method name, ie Serum free light chains (N latex). In our local hospitals, users may need to re-add this test to care-sets.
To make the change of method clear, results will display on a new results line and the method is clearly indicated, eg Kappa free light chains (N latex).
We anticipate some minor delays during transition as we adjust our workflows.
Interpretation of results
Serum free light chain results are useful in investigating suspected B cell malignancy, eg myeloma, lymphoma, and also for prognosis and monitoring of myeloma. This new N latex method has a very similar reference range to the previous Freelites assay but there are methodological differences, so results from the two methods can not be used interchangeably.
Where patients are being monitored using serum free light chains, results will be reviewed by immunology consultants and appropriate comments will be added to aid interpretation (please be aware that a * against a result in Cerner indicates an additional comment is present). Where needed, the laboratory may add on additional testing with the Freelites method for the first sample tested by the new method to assist with interpretation of results during the transition.
Additional information and training
To discuss any individual cases further, please email the immunology consultants (immunologyclinicalenquiries@stgeorges.nhs.uk). A more detailed briefing document has been provided to the haematology teams at St George’s, St Helier, Epsom, Kingston and Croydon hospitals and this can be requested by emailing Dr Rachel Wheeler (r.wheeler@nhs.net). If a clinical team would like additional training on serum free light chains and their interpretation, please email Dr Rachel Wheeler (r.wheeler@nhs.net).
Test names
Routine method from 23 December 2025:
Kappa free light chains (N latex)
Lambda free light chains (N latex)
Kappa:lambda ratio (N latex)
Routine method prior to 23 December 2025:
Kappa free light chains (Freelites)
Lambda free light chains (Freelites)
Kappa:lambda ratio (Freelites)
Method
N latex (Siemens) = rate nephelometry
Freelites (Binding Site) = turbidimetry
Reference range
| Serum free light chains (N latex), routine method from 23.12.25 | Serum free light chains (Freelites), routine method prior to 23.12.25 | |
| Kappa FLC | 6.70 – 22.40 mg/L | 3.75 – 19.30 mg/L |
| Lambda FLC | 8.30 – 27.0 mg/L | 5.76 – 21.75 mg/L |
| K:L ratio | 0.86 – 1.56 | 0.26 – 1.65 |
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