Methods and apparatus for measuring a carbohydrate in a fluid are presented. An amperometric glucose sensor system suitable for glucose monitoring in a biological sample other than blood includes a support member having a sample region defined thereon in fluid communication with a measurement zone including an electrode having an exposed surface area. Biological sample fluid is transported from the sample region to the measurement zone, which includes an exposed catalyst in communication with the electrode providing a minimum sensitivity of at least about 50 micromolar glucose concentration and a noise level of less than about 0.5 nA/.mu.M/mm.sup.2. In some embodiments, at least one of a nanofiltration material and a porous absorbent material is provided between the sample region and the measurement zone.