Rapid laboratory identification of fibrinogen Longmont: a case report and literature review

This study reports a case of a patient with unstable angina with abnormally low fibrinogen (FIB) levels detected during preoperative screening, yet whose clinical manifestations were markedly inconsistent with the test results. Through comparative analysis of multiple methodologies, coagulation curve analysis, manual control, and normal plasma mixing tests, it was found that the optical FIB assay yielded falsely low or failed results (<0.35 g/L), while the magnetic bead assay gave normal results (4.18 g/L; reference range 2-4 g/L) in this case, demonstrating a marked methodological discrepancy. However, as demonstrated in the literature, FIB Longmont may cause method-, reagent-, platform-, and algorithm-dependent discrepancies, with optical signal loss being a major but not exclusive mechanism combined with genetic testing, the diagnosis was ultimately confirmed as a rare dysfibrinogenemia-fibrinogen Longmont. This study aims to explore the laboratory diagnostic characteristics and differential diagnostic approaches for this condition, providing a reference for accurate interpretation of coagulation reports and avoiding misdiagnosis and mistreatment in clinical practice.