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6.2 Borderline Freelite results

Chapter 6

All laboratory tests can produce borderline results, which should be considered in their clinical context and alongside other laboratory test results. Borderline κ/λ sFLC ratios may be attributed to a variety of causes. Increases in FLC concentrations and borderline elevated ratios due to renal impairment in the absence of monoclonal gammopathy are well documented [96][161][162]. For such patients, the use of a renal reference interval for the κ/λ sFLC ratio may reduce the number of false-positive results (Section 6.3).

Borderline high κ/λ sFLC ratios have also been reported in conditions associated with polyclonal inflammatory responses, such as infections, inflammation and autoimmune diseases [161][163][164]. In an audit reported by Marshall et al., 4.9% (47/955) of individuals tested had a borderline abnormal κ/λ sFLC ratio (between 1.67 and 3.2) with no known plasma cell disorder [161]. In the majority of cases this could be attributed to renal impairment or an inflammatory process. The authors commented that borderline low sFLC ratios were infrequently associated with renal impairment or inflammatory states, and that such borderline low ratios should prompt further investigation.

In addition to renal impairment and inflammatory conditions, borderline abnormal Freelite results may occur in a variety of monoclonal diseases encompassing intact immunoglobulin MM, many lymphomas and leukaemias (Chapters 31 and 33), AL amyloidosis (Chapter 28) and monoclonal gammopathy of undetermined significance (MGUS) (Chapter 13). It is now recognised that the probability of a malignant plasma cell disorder increases in relation to the degree of abnormality of the κ/λ sFLC ratio (Chapter 7).