Objectives of the study: Primary, the evaluation of prevalence of resistance to activated protein C (APCR) in thalassemic patients; secondary, the study of prevalence of thrombosis in a group of polytransfused thalassemic patients.

Patients: We evaluated 82 thalassemia major and 3 thalassemia intermedia patients (48 M, 37 F), median age 17 years. 62/85 pts. were HCV-positive, 3/85 HIV-positive, 19/85 were splenectomized, 16/85 had chronic hepatopathy. 20 normal healthy children were recruited as control group. The number of thrombotic events was retrospectively studied in the last 20 years.

Methods: Platelet poor plasma was filtrated and quickly frozen at -80 °C until the time of assay. APC resistance was measured in an activated thrombo-plastin time (Coatest APC Resistance Chromogenix, Sweden) and results were expressed as normalized ratio. All tests were done with plasma diluted 1 in 5 (v/v) F.V deficient plasma and undiluted plasma. Molecular genetic investigation of factor V gene was performed with polymerase chain reaction, followed by digestion of amplified products with restriction enzyme Mnl I.

Results: Data obtained with molecular investigation revealed presence of 4 heterozygous subjects for factor V Leiden (4.7%). Functional tests were able to detect all heterozygotes for factor V Leiden both with undiluted and diluted plasma, and there was no false negative subject. However, undiluted plasma revealed a greater number of false positive subjects(15) than diluted plasma. Therefore tests done with undiluted and diluted plasma revealed a sensibility of 100%, while the specificity was 80% for undiluted plasma and 95% for diluted plasma. Only one thrombotic event was observed among the 85 patients studied, as a case of stroke in a thalassemia intermedia patient with APC resistance. In the same patient an additional thrombogenic risk factor was represented by a pronounced increase in hematocrit at the beginning of her tranfusional regimen.

Conclusions: Our results revealed high prevalence (4.7%) of APCR in thalassemic patients, and demonstrated its importance as an underlyng cause of thrombosis in these patients.