ACCURACY OF A POINT-OF-CARE AMMONIA ANALYZER FOR SCREENING OF BLOOD AMMONIA IN PEDIATRIC PATIENTS WITH INBORN ERROR OF METABOLISM

摘要

Hyperammonemia is an emergency condition that can be life-threatening in pediatric patients. However, the laboratories in most general hospitals in Thailand do not have the testing equipment needed to measure blood ammonia concentration. A point-of-care (POC) ammonia analyzer has recently been introduced that facilitates fast and easy measurement of blood ammonia concentration. To validate the accuracy of this device, we conducted a cross sectional study to compare blood ammonia concentrations measured by the new POC device with concentrations measured by standard enzymatic method in patients with known or suspected inborn errors of metabolism. A total of 20 blood samples were collected from 14 pediatric patients. Scatter plot of blood ammonia concentrations from the POC device and the enzymatic method demonstrated a strong positive correlation, with a Pearson's correlation coefficient of 0.95 (p0.0001) and an intraclass correlation coefficient of 0.93 (95% CI: 0.811-0.974). Bland-Altman plot revealed a mean difference of -7.3 mu mol/l between ammonia concentration measurements from the POC device and the enzymatic method. Using a standard cutoff value, ammonia concentration measurements were in satisfactory agreement in 18 of 20 (90%) samples. Transportation of samples within 30 minutes and EDTA-containing samples did not significantly affect blood ammonia concentrations. In conclusion, POC ammonia testing may be a suitable method for hyperammonemia screening in general hospitals where blood ammonia concentration measurement by standard enzymatic method is not available.