GSTM1 and adenoma: This, combined with the association of Hb content with adenoma characteristics, and with the adoption of a 100 ng ml−1 Hb positivity threshold, allowed for a favourable advanced/not advanced adenoma ratio of approximately 3 : 1 (669/221), as compared to approximately 1 : 1 when guaiac FOBT was employed (Castiglione, 1996).