The Factor V Leiden mutation is associated with a higher blood haemoglobin concentration in women below 50 of the Malmö Thrombophilia Study (MATS).

The aim of this study was to investigate a relationship between FVL-mutation and levels of haemoglobin (Hb) in patients with venous thromboembolism (VTE). From March 1998 to December 2005, 927 consecutive patients with objectively diagnosed VTE were registered in the Malmö Thrombophilia Study (MATS). Female patients with FVL-mutation below 50 years of age had significantly higher median-Hb (133 vs. 126 g/l; P < 0.001) compared to female patients below the age of 50 years without FVL. No significant difference could be found for men or women above 50 years of age or men below 50 years of age. Female patients below the age of 50 years with FVL-mutation and VTE are associated with higher median Hb, and this finding is in accordance with earlier hypothesis that FVL-mutation may have constituted an evolutionary selection advantage.