Falsely prolonged prothrombin time test in a patient with erythrocytosis: a case report

The prothrombin time (PT) test is commonly used to monitor deficiencies in coagulation factors. A prolonged PT may indicate a deficiency of factors II, V, VII, X, and fibrinogen, or the presence of an inhibitor. However, further tests are required to differentiate between a true factor deficiency and the presence of an inhibitor. It is important to note that falsely prolonged PT can lead to misdiagnosis and inappropriate clinical intervention that can have life-threatening consequences. A 19-year-old woman with elevated hematocrit levels and prolonged PT was diagnosed with secondary erythrocytosis due to cyanotic congenital heart disease with ventricular septal defect (VSD). However, further investigation revealed that the prolonged PT result was false. Excess citrate in the blood sample, caused by polycythemia, led to this misleading outcome, resulting in unnecessary and potentially harmful treatment. This incident emphasizes the importance of laboratory personnel and clinicians being aware of the test's limitations. Not only should specialists in thrombosis and hemostasis possess this knowledge, but it is also pertinent for general laboratory staff, as well as laboratory directors and specialists. The significance of accurate laboratory testing for the proper diagnosis and treatment of patients is highlighted in this case.