Interference of M-protein on prothrombin time test - case report

Area of Science:

• Clinical Chemistry
• Hematology
• Immunology

Background:

• Routine coagulation testing is crucial for assessing hemostasis and diagnosing bleeding disorders.
• Monoclonal gammopathy, characterized by the overproduction of a single type of immunoglobulin, can manifest with various clinical complications.

Observation:

• An 88-year-old male presented with unmeasurable prothrombin time (PT) and normal activated partial thromboplastin time (aPTT) during routine testing.
• Subsequent tests revealed persistently unmeasurable PT, prolonged thrombin time (TT), and a visible gelatinous precipitate in refrigerated plasma samples.
• Laboratory findings indicated the presence of monoclonal protein (M-protein), specifically IgG lambda, suggesting monoclonal gammopathy.

Findings:

• The patient's unmeasurable PT results were corrected to 67% activity in a mixing test with normal plasma, indicating in vitro interference.
• Prolonged TT results suggested that the M-protein impacted fibrin polymerization, affecting this global coagulation assay.
• Coagulation factor activities (II, V, VII, X) were within normal or elevated ranges, ruling out factor deficiencies as the cause of PT abnormalities.

Implications:

• This case underscores the importance of recognizing M-protein interference in coagulation assays, particularly PT and TT.
• Abnormal coagulation test results in the presence of M-protein warrant further investigation to differentiate between in vitro interference and true hemostatic abnormalities.
• Accurate diagnosis of monoclonal gammopathy is essential for appropriate patient management and monitoring.