Private Blood Tests are available in Slough through Blue Horizon Medicals at the Thames Valley Spire Hospital. Wexham Street, Wexham, Slough, Berkshire. SL3 6NH. This private and professional clinic blood test location can test patients of ages 18+ but does not have freezing facilities. As phlebotomy is included and the entire process is managed by professionals, this is a VIP blood test, not a DIY blood test.