Provided is a protein comprising an antibody binding site that binds to a sulfated epitope of a Wnt pathway protein that is not Wnt5A, Wnt1l, or Wnt3a. Also provided is a composition comprising an isolated and purified Wnt pathway protein, where the protein is sulfated but not glycosylated. Additionally provided is a preparation of a Wnt pathway protein comprising at least one sulfation site and at least one glycosylation site, where all of the Wnt pathway protein in the preparation is glycosylated but not sulfated. Further provided is a composition comprising a peptide less than 75 amino acids or amino acid analogs, the peptide consisting of a fragment of a Wnt pathway protein, wherein the fragment is sulfated. A modified Wnt pathway protein comprising a sulfation site that is not present in the native Wnt pathway protein is also provided. Also provided is a method of detecting or quantifying a sulfated Wnt pathway protein in a preparation. Additionally, a modified Wnt pathway protein lacking a sulfation site that is present in the native Wnt pathway protein is provided. Also provided is methods of treating a subject having a disease exacerbated by Wnt activation. Additionally, a method of treating a subject having a disease exacerbated by Wnt inhibition is provided.