It is also important to recognize the clinical experience and expertise of GPs in assessing the nature and severity of symptoms: ‘gut feelings for cancer’ can be conceptualized as a rapid summing up of multiple verbal and non-verbal patient cues.36 Thus, f-Hb should not be used by secondary care to refuse requests from GPs to have a patient investigated, but rather it should be used by the GPs themselves to assist in reaching an objective decision as to whether or not to refer for further investigation. Here, GSTM1 is linked to cancer.