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Purpose:To determine if intravenous (IV) glucose boluses cause significant alterations of serum potassium ([K+]) levels.Methods:A prospective, descriptive study of patients ≥18 years of age presenting with altered levels of consciousness (ALOC) to paramedics in the prehospital setting or to the emergency department (ED) of a community teaching hospital and who received 50% Dextrose (D50) intravenously (IV). At presentation, a blood sample (PRE) was obtained prior to D50 therapy. For patients treated by paramedics, a second blood sample (POST) was obtained upon arrival at the ED. For patients who initially were seen in the ED, the POST sample was obtained one hour after D50 therapy. Both samples were analyzed to determine [K+] and glucose levels.Results:Over a seven-month period, 40 patients met study criteria. The average age was 46±20 years. Sixty percent of patients (24/40) had PRE blood sugars (BS) <80 mg/dl (mean PRE BS = 37±12 mg/dl; mean POST BS = 140±45 mg/dl) and 40% (16/40) had a PRE BS >80 mg/dl, (mean PRE BS = 241±255 mg/dl; mean POST BS = 274±237 mg/dl). The mean PRE [K+] was 4.1±0.8 mEq/L and the mean POST [K+] was 4.2±0.7 mEq/L. Forty-two percent of patients (17/40) had a <5% change in [K+], 33% (13/40) had a >5% increase in [K+], and 25% (10/40) had a >5% decrease in [K+]. Ten percent of patients (4/40) had a >20% increase in [K+], and 3% (1/40) had a ≥20% decrease in [K+]. No patient was treated for symptoms of either hyperkalemia or hypokalemia.Conclusion:Boluses of IV glucose produce unpredictable changes in [K+]. The majority of these changes probably are insignificant clinically.