Introduction:
Haemophilia A (HA) is a rare bleeding disorder. Patients with severe HA have a factor VIII activity of < 1%. The clinical picture of severe HA consists of a propensity for spontaneous haemorrhages to the skin, muscles, joints, and internal organs. To prevent severe complications of bleeds, patients with severe HA receive prophylaxis with deficient clotting factor. Obese people have larger absolute fat free mass (FFM) as well as fat mass than non-obese individuals of the same age, gender and height. Factor VIII (FVIII) concentrates are typically confined to the vascular space. Although the pharmacokinetics (PK) based FVIII dosing is becoming a standard in tailoring the prophylaxis for HA patients, the majority of them are still dosed according to total body weight and this may result in an overdose of FVIII. This study aimed to evaluate the PK of FVIII considering patients’ body weight and body composition using electrical bioimpedance.

Material and methods:
Twenty-one boys with severe HA undergoing plasma-derived factor VIII prophylaxis were enrolled in the study. Patients underwent physical examination, body weight and height measurements, had body composition assessed using electrical bioimpedance, FVIII concentration was measured before and 30 min after FVIII administration, and FVIII recovery was evaluated. Patients completed a questionnaire regarding treatment, physical activity, and bleeding.

Results:
Of the patients who underwent the study, 47.6% had a normal body mass index (BMI), 42.8% were overweight, and 9.5% of patients were underweight. There was a correlation between patients’ BMI and FVIII recovery, FFM and FVIII recovery, and fat mass and FVIII recovery. No relationship was found between FVIII recovery and bleeding rate.

Conclusions:
Determining factor VIII dosage according to FFM requires further study.