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 . 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).
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).