Mass spectral determination of fasting tear glucose concentrations in nondiabetic volunteers.

BACKGROUND There is considerable disagreement regarding the concentration of glucose in tears and its relationship to the concentration in blood. Improved sampling and analysis methods may resolve these discrepancies and possibly provide a basis for in situ tear glucose sensors. METHODS We used liquid chromatography (LC) with electrospray ionization mass spectrometry (ESI-MS) to determine glucose in 1-muL tear fluid samples obtained from 25 fasting study participants. Tear fluid was collected with microcapillaries and a slitlamp microscope. RESULTS The median (range) of fasting tear glucose concentrations was 28 (7-161) micromol/L or 0.50 (0.13-2.90) mg/dL. The SD of tear glucose measurements for individuals varied linearly with the mean tear glucose concentration and was approximately half of the mean. We found no significant difference in tear glucose concentrations between contact lens users and nonusers (P = 0.715). We observed significant correlations between fasting blood and tear glucose concentrations (R = 0.50, P = 0.01). CONCLUSIONS Our tear fluid collection and analysis method enables reliable measurement of equilibrium, fasting tear glucose concentrations. These concentrations are lower than those previously reported for nondiabetic persons. Larger population studies are required to determine correlations between blood and tear glucose concentrations and to determine the utility of contact lens-based sensors for the monitoring of diabetes. Our methods are applicable for study of other tear fluid analytes and may prove useful for monitoring other disease states.