Abstract
Introduction. In vitro laboratory tests to diagnose of plasma cell myeloma vary considerably in sensitivity, specificity and positive and negative predictive values. We compared the performance of quantification of free immunoglobulin light chains with other methods used to detect a monoclonal protein in serum and/or urine.
Objective. Compare sensitivity, specificity and positive and negative predictive values of several in vitro laboratory tests to detect monoclonal proteins in serum and urine in persons with plasma cell myeloma.
Methods. 70 subjects with plasma cell myeloma and 50 controls were studied. Diagnostic tests included: (1) quantification of free and total immunoglobulin light-chains by immune assays; (2) immune fixation of heavy-and light-chains in serum and urine after gel electrophoresis; and (3) serum protein capillary electrophoresis. Diagnosis of plasma cell myeloma was based on clinical and radiological criteria, bone marrow examination and flow cytometric immune phenotyping with monoclonal antibodies to CD56, CD19, CD138 (CD38) and CD45. Sensitivity, specificity and positive and negative predictive values for each tests were estimated from contingency tables.
Results. Quantification of free immmunoglobulin light-chains had the highest sensitivity and specificity and best positive and negative predictive values. Immune fixation of serum immunoglobulins was next best. Quantification of total immunoglobulin light-chains was the least sensitive and specific with the worst positive and negative predictive values. Quantitation of free light-chains had the additional advantage of objectivity (independence from observer bias). The immune fixation test was the most subject to observer bias.
Conclusion. Quantification of free immunoglobulin light-chains had the best sensitivity, specificity and positive and negative predictive values for diagnosing plasma cell myeloma. (Table 1)
No relevant conflicts of interest to declare.
