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39.3. United Kingdom National External Quality Assessment Service scheme

Chapter 39

The United Kingdom National External Quality Assessment Service (UK NEQAS) for Immunology, Immunochemistry & Allergy (IIA) provides a Monoclonal Protein Identification scheme that is accredited by the United Kingdom Accreditation Service (UKAS). The scheme has incorporated sFLC analysis since 2005 and there are six distributions per year comprising unmatched serum and urine samples. Over 380 UK and international laboratories are registered for the scheme, and approximately 170 report quantitative sFLC results. Prior to June 2015 (up to and including distribution 152) quantitative sFLC were reported separately to other laboratory test results but have since been amalgamated into a single report. sFLC results are categorised by both instrument type and reagent manufacture.

Past distributions have highlighted the need for all participants to be aware of sFLC assay technical issues. For example, the Dade Behring BN™II Freelite κ sFLC results for UK NEQAS Distribution 095 were bimodal: peaks were observed at 143 mg/L and 1001 mg/L (Figure 39.6). It is likely that these two peaks corresponded to those participants who did not, and those who did, screen for sFLC antigen excess (following the dilution protocol in the product insert). The phenomenon of antigen excess is further discussed in Section 7.4.

Since 2012, Siemens N Latex FLC assays have been reported as a separate user group. This has allowed the absolute values reported by Freelite and N Latex FLC assays to be compared. For example in Distribution 136, N Latex FLC results were significantly lower than those reported by Freelite (Figure 39.7).

A recent review article by Carr-Smith et al. [868] compared sFLC results from the 2014 UK NEQAS distributions for Freelite on the Binding Site SPAPLUS® against N Latex FLC on the Siemens BN™II (Table 1). For all distributions, the average inter-laboratory variation (%CV) for κ FLC results was lower for Freelite compared with N Latex FLC assays. For λ FLCs, the mean %CV of Freelite results was superior (4/6 distributions) or equivalent (1/6 distributions) to N Latex FLC results for the majority of samples. The results also indicate that the absolute values reported by two assays do not compare well; this is discussed further in Section 8.5.3.

Instrument – Assay

(distribution)

κ FLC

λ FLC

n

Mean, mg/L

CV, %

n

Mean, mg/L

CV, %

SPAPLUS – BS (141)

35

5.59

10.3

35

17.39

8.6

BNII – SMS (141)

16

4.23

12.6

16

334.38

16.6

SPAPLUS – BS (142)

36

722.59

7

34

3.65

34.1

BNII – SMS (142)

13

152.25

44.5

13

0.36

12.7

SPAPLUS – BS (143)

39

9.67

9.7

39

13.21

7.5

BNII – SMS (143)

15

6.42

12.2

15

7.2

12.3

SPAPLUS – BS (144)

40

975.6

7.9

40

20.7

5.9

BNII – SMS (144)

19

171.2

68.8

19

22.21

10.5

SPAPLUS – BS (145)

44

82.4

16.2

41

2.9

10.5

BNII – SMS (145)

18

41

58.2

18

3.45

30.5

SPAPLUS – BS (146)

41

1.55

9.1

45

894

13.1

BNII – SMS (146)

23

1.21

19.8

24

545

13.1

Table 1. Summary of 2014 UK NEQAS Monoclonal Protein Identification scheme results for Freelite (BS) on the SPAPLUS and N Latex FLC (SMS) on the BNII [868].

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