Abstract: Alanine transaminase (ALT) is still the most sensitive marker for evaluating the damage of liver cells.ALT measurements may be affected by common nonpathological factors such as gender,age,pregnancy,different physiological conditions,circadian rhythm,diet,drinking,smoking,strenuous exercise,metabolic factors,drugs,blood collection methods,and specimen collection,transmission,and preservation.It is important to emphasize the definition of limits of normal ALT and the influence of the above-mentioned non-pathological factors on its test results.