DETERMINATION OF AMMONIA IN EAR-LOBE CAPILLARY BLOOD IS AN ALTERNATIVE TO ARTERIAL BLOOD AMMONIA

Blood ammonia determination is a laboratory test to diagnose hepatic e ncephalopathy. Arterial blood is superior to peripheral venous blood a mmonia because of ammonia metabolism in muscle. We have compared capil lary with arterial whole blood ammonia as capillary sampling is an att ractive alternative. Ear-lobe capillary blood ammonia (ECA) was determ ined in all 173 persons studied, fingertip capillary blood ammonia (FC A) in 46 of these and arterial blood ammonia (AA) in 113. Of the 173, 60 were healthy (H), 64 were patients, not liver diseased (NLD) and 49 had liver disease (LD). Reference values, median and ranges, mu mol N H3-N/l: AA, NLD, n = 64: 17 (7-42); EGA, H = NLD (P = 0.9), n = 124: 2 0 (7-45); FCA, H = NLD (P = 0.8), n = 33: 70 (29-151), Within the NLD group (n = 64) AA values (range 7-42) were little but significantly lo wer than the ECA values (range 7-45, P = 0.002), FCA NLD > AA NLD (n = 14, P < 0.0001); FCA H + NLD > ECA (n = 33, P < 0.0001). AA correlate d very well with EGA, r = 0.87 (n = 113, P < 0.0001) and less well wit h FCA, r = 0.56 (n = 27, P < 0.01). ECA correlated with FCA, r = 0.51 (n = 46, P < 0.001). Ear-lobe capillary blood ammonia thus accurately reflects arterial ammonia and is an attractive alternative. The higher fingertip ammonia may be due to contamination with ammonia-rich sweat from finger grooves, regardless of the precautions taken.