Analytical Interference in Alanine Aminotransferase Determination in Patients with Monoclonal Gammopathy.

Background: Analytical interferences are very common in clinical laboratories, so professionals must develop strategies for their detection, avoiding incorrect results that can lead to inappropriate diagnoses and treatments.

Methods: An isolated 1040 error (absorbance-related) in the Alanine Aminotransferase2 (ALT2) assay performed on the Abbott Alinity c that occurred in 158 samples over 7 months was investigated. Highly lipemic or hemolyzed samples were excluded, and an error due to an increased concentration of total proteins was ruled out, all of which are documented analytical interferences.

Results: We isolated immunoglobulin (Ig) with an increased concentration (monoclonal components: 149 IgM, 7 IgG, and 2 IgA) from all analyzed samples, so the presence of this error solely in the alanine aminotransferase (ALT) assay had a 100% positive predictive value for monoclonal gammopathy. Serum viscosity was elevated in all cases, which is the reason for the detected interference. Treatment of IgM samples with dithiothreitol confirmed that dissociation of the pentamers eliminates the error in ALT determination.

Conclusions: The detection of this interference in samples from patients without recent immunoglobulin determinations indicates the presence of a significant and isolated increase in the concentration of one of them, potentially leading to the diagnosis of a previously unknown monoclonal gammopathy.