 This study will involve the patient having blood samples taken by two different methods at each of the time points described above. In the first method, a butterfly needle will be used to gain intravenous access at the antecubital fossa, and a heparinised vacutainer will be used to collect a 4ml blood sample. The needle will then be removed and the venepuncture site dressed with a plaster. In the second method, a single-use safety lancet will be used to puncture the skin on the finger, and a small pipette used to collect a small quantity of blood. The entire pipette will be transferred to a sample tube for later processing. The puncture site on the finger will then be dressed with a small plaster. The exact start and end times for each sample will be recorded using a radio-controlled standard clock. 