Determination of ammonia in cerebrospinal fluid using the indophenol direct method

We have determined ammonia in cerebrospinal fluid (CSF) with the indophenol direct method. The results were compared with an enzymatic method. The met hod is very simple, and precision (coefficient of variation 1.6%) and linea rity (r = 0.9999, p < 0.001) of the method are excellent. The recoveries of the method are very good (within-sample recovery: range 88-93, median 93%; between-sample recovery: 88-93, median 91%). in a population of 23 neurolo gical patients not suffering from liver disease, the reference values range d from 8 to 26, median 18 mu M. Males and females did not differ (p = 0.5). The values obtained with the indophenol method were equal to the enzymatic method (range 9-28, median 18 mu M, p = 0.6). On storage in the deep freez e (-20 degrees C), there was no change in CSF ammonia concentration for at least 1 mo. When stored at 4 degrees C (refrigerator), ammonia determinatio ns have to be performed within 2 d. CSF storage at room temperature results in artificially elevated ammonia levels and should be avoided.