Effect of time and storage conditions of Chemstrip bG on estimating blood glucose aboard ambulances.

This study tested the hypothesis that the age of Chemstrip bG aboard ambulances is not associated with decline of accuracy. This was accomplished by removing and testing Chemstrips bG from ambulances in Salt Lake City, Utah, U.S.A. Chemstrips were developed with three concentrations of glucose (2.0, 3.8, 12.4 mmol/L; 35, 68, 223 mg/dL, respectively) in a blinded manner by three different researchers and compared with fresh controls and with the Dimension Analyzer-derived glucose. Results showed that older Chemstrips read significantly higher than fresh strips at each value of glucose tested (p less than 0.05). Increased age was associated with higher readings. Therefore, it is possible that cases of hypoglycemia may be missed by reliance on older Chemstrips. While fresh strips tended to underestimate glucose at 12.4 mmol/L, age and storage aboard ambulances tended to reverse this underestimation; older Chemstrips were associated with a more accurate reading at 12.4 mmol/L. Older age was also associated with increased standard deviation of Chemstrips. Unless this bias is considered in clinical practice, it might result in a failure to detect and treat a patient with hypoglycemia. Chemstrips aboard ambulances should be interpreted with caution when evaluating a patient on the threshold of hypoglycemia. Meanwhile, institution of a quality control program is indicated. This would include periodic testing, but might also include storage of Chemstrips, when not in use, in a climate-controlled area either on or off the ambulance.