Levine R J, Conn H O
J Clin Invest. 1967 Dec;46(12):2012-20. doi: 10.1172/JCI105690.
Plasma levels of tyrosine were assayed in the fasting state and after oral administration of either tyrosine (tyrosine tolerance test) or phenylalanine (phenlyalanine conversion test) in normal subjects and in patients with hepatitis, biliary obstruction, or cirrhosis. Fasting tyrosine levels tended to be slightly increased in patients with hepatitis and biliary obstruction and markedly increased in patients with cirrhosis. Tyrosine tolerance tests in patients with cirrhosis were characterized by larger than normal increments in tyrosine levels and by delayed returns toward fasting levels. The results of phenylalanine conversion tests were abnormal in approximately one-half of patients with either hepatitis or biliary obstruction and four-fifths of patients with cirrhosis. Abnormalities were characterized by elevated fasting plasma tyrosine levels, or small and delayed increments in tyrosine levels, or both. Abnormal phenylalanine conversion test results in patients with cirrhosis did not correlate closely with any clinical feature of cirrhosis or with the results of any standard liver function test; there was positive correlation only with abnormal ammonia tolerance, a test of portalsystemic shunting. Tests of tyrosine metabolism do not appear to be useful for routine clinical assessment of liver function. Tyrosine tolerance tests and phenylalanine conversion tests done for purposes of diagnosis of other diseases may yield misleading results in patients with liver disease.
在正常受试者以及患有肝炎、胆道梗阻或肝硬化的患者中，测定了空腹状态下以及口服酪氨酸（酪氨酸耐量试验）或苯丙氨酸（苯丙氨酸转化试验）后的血浆酪氨酸水平。肝炎和胆道梗阻患者的空腹酪氨酸水平往往略有升高，而肝硬化患者则显著升高。肝硬化患者的酪氨酸耐量试验表现为酪氨酸水平升高幅度大于正常，且恢复至空腹水平的时间延迟。约一半的肝炎或胆道梗阻患者以及五分之四的肝硬化患者的苯丙氨酸转化试验结果异常。异常表现为空腹血浆酪氨酸水平升高，或酪氨酸水平升高幅度小且延迟，或两者皆有。肝硬化患者苯丙氨酸转化试验结果异常与肝硬化的任何临床特征或任何标准肝功能试验结果均无密切关联；仅与门体分流试验——氨耐量异常呈正相关。酪氨酸代谢试验似乎对肝功能的常规临床评估并无用处。为诊断其他疾病而进行的酪氨酸耐量试验和苯丙氨酸转化试验，在肝病患者中可能会产生误导性结果。
