Objective: To determine the utility of the serum free light chain (FLC) assay for routine screening of light chain amyloidosis (AL) in patients with heart failure. Patients and Methods: We studied consecutive new patients referred to the Heart Failure Clinic who had the FLC assay performed for routine screening at Mayo Clinic's campus in Rochester, Minnesota, from January 1, 2011, through December 31, 2015. An FLC ratio between 0.26 and 1.65 was considered normal. Results: Of the 1173 patients in the study (mean age, 64±15 years), 207 had an abnormal FLC ratio. Light chain amyloidosis was diagnosed in 0.5% of all patients (6 of 1173) and in 2.9% of those with an abnormal FLC ratio (6 of 207). To increase the pretest probability of an abnormal FLC ratio in predicting AL, we considered patients with an N-terminal pro B-type natriuretic peptide level of 5000 pg/mL or greater (to convert to pmol/L, multiply by 0.1182) and a left ventricular posterior wall thickness of 13 mm or greater; this increased the diagnostic yield to 66.7% (6 of 9). Conclusion: The prevalence of AL in patients with heart failure could be 0.5% or higher. Compared with the use of the serum FLC assay for routine screening, a targeted approach of the serum FLC assay in those with higher N-terminal pro B-type natriuretic peptide level (≥5000 pg/mL) and increased posterior wall thickness (≥13 mm) has a markedly higher yield for the diagnosis of AL.
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