Upconverting phosphors are inorganic crystals with interesting optical properties, including the ability to convert infrared radiation to emission at shorter wavelengths. In this paper we present the utilization of nanosized beta-NaYF4:Yb3+, Tm3+, synthesized in the presence of K+, emitting at 365 nm under 980 nm excitation as an internal light source in glucose sensing dry chemistry test strips. The feasibility of the nanoparticles as an internal UV light source was compared to the use of an external broadband lamp. The results obtained from glucose measurements using UCNPs were in agreement with the traditional method based on measuring reflectance using an external UV light source. In addition the multiple emission peaks of UCNPs offered the possibility of using them as a control signal to account for various sources of error arising in the assay. The high penetration depth of the NIR-excitation made it also possible to excite the UCNPs through a layer of whole blood, giving more freedom to the design of the optical setup.