Inaccuracy of glucose monitoring may derive from test strip, patient, pharmacological, environmental, and other factors. Incorrect results may cause serious harm and change clinical decisions. 2,3 To ensure reliable results, POC devices and test strips should be stored and operated according to manufacturer specifications. In tropical settings, temperature and relative humidity may exceed specified ranges.Our goal was to assess the effects of storage temperature, operating temperature, and operating relative humidity (RH) when ambient conditions in patient ward areas naturally exceeded manufacturer limits because of the tropical setting of Siriraj Hospital. During ISO 22870 4,5 certification inspection, we discovered out-of-limit temperature and RH discrepancies that had to be investigated and corrected. Methods Glucose Meters and Test StripsWe evaluated the photometric SureStep®Flexx meter, SureStep™ Hospital glucose test strips, and control solutions Background: Hospitals in tropical countries experience conditions that exceed manufacturer temperature and humidity limits for point-of-care (POC) glucose reagents. Our goal was to assess the effects of out-of-limits storage temperature, operating temperature, and operating humidity on POC glucose measurement reliability.Methods: Quality control measurements were performed monthly using glucose test strips stored under controlled conditions and in inpatient wards under ambient conditions. Glucose test strips were evaluated in groups organized by operating temperatures of 24-25 (group 1), 28-29 (group 2), and 33-34°C (group 3), and relative humidity (RH) of ≤70 (group A), ~80 (group B), and ~90% (group C). Results:Glucose results for different storage conditions were inconsistent. Measurements at higher operating temperatures had lower values with mean differences of -2.4 (P < .001) and -36.5 (P < .001) mg/dL (28-29 vs 24-25°C), and -3.6 (P < .001) and -37.4 (P < .001) mg/dL (33-34 vs 24-25°C) for low and high control levels, respectively. Measurements at higher RH had lower values with mean differences of -4.0 (P < .001) and -13.2 (P < .001) mg/dL (~80 vs ≤70% RH), and -5.8 (P < .001) and -16.6 (P < .001) mg/dL (~90 vs ≤70% RH) for low and high levels, respectively. Conclusions:High temperature and high RH decreased glucose concentrations for the POC oxidase-based system we evaluated. We recommend that individual hospitals perform stress testing, then determine if maximum absolute differences, which represent highest risk for patients, are clinically significant for decision making by using error grid analysis.