title: Interference of M-protein on prothrombin time test - case report.
abstract: The aim of this report was to present a case of interference on prothrombin time (PT) test that directed further laboratory diagnostics and resulted with final detection of monoclonal gammopathy in an 88-year old man. Routine coagulation testing during medical examination at Emergency Department revealed unmeasurable PT (< 7% activity) and activated partial thromboplastin time (aPTT) within reference range. After repeated sampling for coagulation testing, PT was unmeasurable again, as well as fibrinogen level (< 0.8 g/L), thrombin time (TT) was significantly prolonged (107 seconds) and aPTT was within reference range. In both plasma samples refrigerated at 4 ˚C overnight, white gelatinous precipitate was visible between the cell and plasma layers and the presence of monoclonal protein (M-protein) was suggested in our patient. Further laboratory diagnostics revealed total serum proteins at concentration of 123 g/L and the presence of M-protein IgG lambda (λ) at concentration of 47.1 g/L. These results suggested monoclonal gammopathy as an underlying pathophysiological condition in our patient. Activities of coagulation factors II, V, VII and X were within reference ranges or increased. These results and correction of unmeasurable PT result to 67% in mixing test with commercial normal plasma suggest in vitro rather than in vivo interference of M-protein on PT result. In contrast, significantly prolonged TT results in all analysed samples suggest impact of M-protein on this global coagulation test due to possible effect on fibrin polymerization.
authors.affiliation: Clinical Institute of Chemistry, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Sandra
authors.initials: S
authors.lastname: Margetić
authors.affiliation: Clinical Institute of Chemistry, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Ivana
authors.initials: I
authors.lastname: Ćelap
authors.affiliation: Clinical Institute of Chemistry, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Lora
authors.initials: L
authors.lastname: Dukić
authors.affiliation: Clinical Institute of Chemistry, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Ines
authors.initials: I
authors.lastname: Vukasović
authors.affiliation: University Department of Internal Medicine, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Lucija
authors.initials: L
authors.lastname: Virović-Jukić
mesh_terms: D000369:Aged, 80 and over; D001777:Blood Coagulation; D064211:Connectin / Q000378:metabolism*; D006801:Humans; D008297:Male; D010265:Paraproteinemias / Q000175:diagnosis* / Q000473:pathology; D011516:Prothrombin / Q000378:metabolism; D011517:Prothrombin Time / Q000379:methods*
chemical_list: D064211:Connectin; D011516:Prothrombin
keywords: M-protein; interference; monoclonal gammopathy; prothrombin time; thrombin time