Hepatic encephalopathy (HE) is associated with elevated arterial
ammonia levels. The relationship is variable, in part due to
ammonia methodology. One method, based on the
indophenol reaction (IPh), is interfered with a number of
amino acids including all
aromatic amino acids. We have determined arterial
ammonia simultaneously with the Blood
Ammonia Checker II (BAC) as reference method and with the IPh method. The difference BAC-IPh, mumol/l, was assumed to express the interference in the
indophenol method (IFI) by
amino acids. It may be positive or negative. The aim was to establish the value of BAC in comparison with IPh in the diagnosis of
liver disease and overt HE and to assess any added value of IFI. Of two reference groups without disturbances, A (n = 39) had not and B (n = 13) had
encephalopathy. Group C consisted of 125 liver patients (34 no
cirrhosis, 91
cirrhosis) of which 55 had no manifest HE (C:HE-) and 70 had HE (C:HE+). Median BAC
ammonia nitrogen (NH3-N), mumol/l: A 21, B 35, C 80, C:HE - 57 and C:HE+ 98 (A < B < C and A < B < C:HE - < C:HE +, P < 0.001). Median IPh NH3-N, mumol/l: A 27, B 30, C 30, C:HE - 25 and C:HE + 35 mumol/l (A = B = C and C:HE - < C:HE+, P < 0.01). IFI medians: A -6,
B 3, C 40, C:HE - 29 and C:HE + 58 mumol/l (A < B (P < 0.05) < C (P < 0.0001); A, B < C:HE - and C:HE+; C:HE- < C:HE + (all P < 0.0001)). While BAC correlated weakly with IPh in the (sub)groups C, C:HE-, C:HE+ (r = 0.3, 0.3, 0.4, P < 0.05), it correlated strongly with IFI (r = 0.9, 0.9, 0.8, P < 0.0001). There was no correlation between IPh and IFI. BAC, as well as IFI, could discriminate all liver patients (C) from both reference groups A and B with 100% positive likelihoods. BAC, IPh and IFI could discriminate between HE- and HE+. To differentiate
cirrhosis from non-
cirrhosis the specificity of IPh was uniformly high and the sensitivity satisfactory, whereas BAC had a high sensitivity but an insufficient specificity. In conclusion, in blood, BAC is the
ammonia determination of choice. It differentiates between reference groups (encephalopathic or not) and
liver disease and the more so HE. The combination of BAC and IPh (indicating IFI) may eventually be shown useful to rapidly assess the severity of underlying
liver disease in HE patients. In other
biological fluids, IPh is excellent when the inhibiting influence of non-
protein nitrogen substances is absent or can be eliminated.