Int J Emerg Med (2009) 2:117–120 0.34 to 0.56. It was noted that 86.5% of Na+ values obtained on the ABG machine were lower than those on the AA. Sodium analysis was stratified based upon the standard laboratory values, and 135–145 mmol/l was considered as normal serum sodium. Anything above was considered hypernatremia. Patients with serum sodium 120–135 mmol/l were considered as borderline hyponatremic, and patients with serum sodium less than 120 mmol/l were diagnosed as hyponatremic (Table 3). Clinically this was a more signifi- cant group because only at Na<120 did the clinicians feel it important to correct sodium emergently. Analysis of the sodium measurements in the group of patients with normal sodium revealed a significant differ- ence between the two measures (p = 0.005; hypothesis rejected). However, the mean difference between the two measuring methods was 3.4 mmol/l, which was within the acceptable limit defined in the US CLIA 2006. There was no significant difference in sodium measure- ments by AA and ABG for patients with hypernatremia (mean difference 3.8 mmol/l; p = 0.3847, hypothesis accepted). However, because of the small sample size (n = 5) in this subgroup, we were underpowered to detect a difference. In the group of patients with borderline hyponatremia (serum sodium 120–135 mmol/l) and hyponatremia (serum sodium <120 mmol/l), the mean difference between the two measurements was 7.4 mmol/l and 12.8 mmol/l (p < 0.0001 for both subgroups), effectively making the ABG measure- ments unreliable. Analysis of the potassium values (Table 4) obtained from the AA and the ABG gave a mean difference of 0.46 mmol/l with a standard error of 0.03 mmol/l. There was no significant difference (p=0.2679, hypothesis accepted) between K+ measured by the ABG (3.7 mmol/l, SD 1.9) and AA (mean 3.9 mmol/l, SD 1.8). The maximum difference in measured potassium value was 2.4 mmol/l, and the minimum difference was 0 mmol/l. The correlation coefficient (r) was 0.72. The adjusted r2 was within a 95% confidence interval of 0.42 to 0.62. A total of 71.5% of the K+ values obtained on the ABG was lower than the AA. Table 3 Stratified analysis of difference between Na+ measured by AA and ABG Mean SD Max. Min. difference difference difference difference mmol/l mmol/l mmo/l mmol/l Group mmol/l >145 135–145 120–135 <120 3.8 3.4 7.4 12.8 2.77 2.35 4.26 7.19 8.0 12.0 22.0 30.0 1.0 0.0 0.0 6.0 P value 0.3847 0.0051 <0.0001 <0.0001 Table 4 Statistical analysis of potassium Sample Blood gas analyzer Auto-analyzer Mean mmol/l 3.7 3.9 119 SD mmol/l 1.9 1.8 Potassium values were stratified (Table 5) based upon the standard laboratory values. Patients with K+ 3.5– 5.0 mmol/l were normo-kalemic, values above 5.0 mmol/l were considered as hyperkalemia, and those below 3.5 mmol/l were considered as hypokalemia. The mean differences in patients with hyperkalemia, normokalemia, and hypokalemia were 0.44 mmol/l (SD 0.05), 0.46 mmol/l (SD 0.03), and 0.42 mmol/l (SD 0.02), respectively, all of which are less than the US CLIA 2006 guideline of 0.5 mmol/l. Discussion Point-of-care analyzers are force multipliers for clinicians working in the areas of critical care and emergency medicine. They have been proven to benefit clinical decision-making by reducing the turnaround time for routine biochemical investigations. Time critical decisions are enabled by point-of-care analyzers when biochemical parameters are beyond their normal limits. Several kinds of point-of-care testing equipment are in vogue in clinical practice today, and they have been widely evaluated in varied environments. Point-of-care testing has gained special favor in emer- gency transport systems, critical care departments, and cardiothoracic surgical departments, as is shown by the large volume of systems developed for all of these areas [12–14]. However, high operational costs are a deterrent to the application of specialized point-of-care equipment in developing countries [15]. Direct costs have been decreasing Table 5 Stratified analysis of the difference between K+ measured by AA and ABG Group mmol/l >5.0 3.5–5.0 <3.5 No. of values 58 106 36 Mean difference mmol/l SD difference mmol/l Max. difference mmo/l Min. difference mmol/l 0.44 0.46 0.42 0.05 0.03 0.02 1.8 1.6 2.4 0.0 0.0 0.0