The disclosure relates to an alginate oligomer of 2 to 75 monomer residues, wherein said monomer residues do not carry a sulphate group, for use as a blood anticoagulant in clinical and non-clinical applications, including in vivo, ex vivo and in vitro contexts. The invention further provides for the use of such an alginate oligomer in preparing a product or device having a reduced capacity to promote blood coagulation, wherein said alginate oligomer is provided at or on a surface of said product or device. Such products and devices form a further aspect of the invention.