Use of interval-specific likelihood ratios improves clinical interpretation of serum FLC results for the diagnosis of malignant plasma cell disorders

Abstract: Background: We examined whether the use of test result interval-specific likelihood ratios (LR) could improve the clinical interpretation of serum FLC κ/λ ratio for the diagnosis of malignant plasma cell disorders. Methods: We calculated LRs for different FLC κ/λ intervals using sera from patients diagnosed with intact multiple myeloma (MM), light chain MM (LCMM), non-secretory MM (NSMM) and light chain amyloidosis (AL-A). Consecutive patients with a clinical suspicion of a monoclonal B-cell disorder that were diagnosed with MGUS or no B-cell monoclonal disorder served as the disease control group. Results: Using LRs for different test result intervals, a distinction can be made between FLC κ/λ ratios that are within the normal diagnostic range, ratios that are inconclusive (1.66–5.0, LR±1), ratios that indicate the possible presence of a malignant plasma cell disorder (0.05–0.25 and >5.0–10, LR±10) and ratios that were suggestive of a malignant plasma cell disorder (<0.05 or >10; LR±50). A FLC κ/λ ratio within the normal diagnostic range virtually excluded LCMM and AL-A, but not intact MM or NSMM. Conclusions: Interpreting serum FLC κ/λ ratios using LRs for different result intervals improves the clinical interpretation for the diagnosis of malignant plasma cell disorders excluding plasmacytoma. [Copyright &y& Elsevier]