Abstract: A kit useful for determination of non-human mammal TK1 in a sample is disclosed. The kit comprises a first antibody immobilized to a support or intended to be immobilized to a support. The kit also comprises a second antibody. One of the antibodies has specificity for a peptide consisting of a first amino acid sequence from a C-terminal region of non-human mammal TK1 and the other antibody has specificity for a peptide consisting of an amino acid sequence from an active site of TK1 or for a peptide consisting of a second amino acid sequence from the C-terminal region.