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8.5.7. Diagnostic performance in cast nephropathy

Chapter 8

The International Kidney and Monoclonal Gammopathy Research Group (IKMGRG) recommend the use of SPE and sFLC analysis to screen for monoclonal disease in patients presenting with acute kidney injury (Chapter 27) [22]. The IKMGRG suggest that if the concentration of monoclonal FLCs is ≥500 mg/L in patients with acute kidney injury (AKI), a diagnosis of tubular interstitial pathology is likely, and the most common renal lesion in such cases is cast nephropathy [213]. For such patients, further haematological work-up and prompt treatment, to reduce FLC production, is essential.

In the only study performed to date using the Siemens N Latex FLC assays in the context of AKI, the authors concluded that the IKMGRG recommendations could not be carried out satisfactorily [220]. In this study, five of the 28 patients (18%) with AKI secondary to MM were misclassified by the N Latex FLC assays. For one patient, the N Latex FLC assay reported a λ FLC concentration of 1 mg/L, whereas a value of 1810 mg/L was reported by the Freelite assay. Once again, this suggests that the pathogenic monoclonal λ FLC clone was not recognised by the monoclonal antibody-based assay.