I smoke cigarettes but my ammonia blood test came back normal. shouldn't it be higher than normal due to smoking? is my liver not working?

Not related: Ammonia level is not related to smoking, but to liver dysfunction.

Not necessarily: The combination of ammonia in cigarette by the industry, to enhance the effect of nicotine, may be in the chemical form not causing higher ammonia level in the blood, I am not sure. But if your doctor ordered the ammonia level to check something other than documenting effect of smoking, you can focus on that to feel relieved that the test was normal.

No sign liver issue: A working liver processes the ammonia that is produced during digestion of food. A failing liver cannot work well enough, so less ammonia gets processed. The unprocessed ammonia gets into the bloodstream and from there into the brain, where it causes symptoms such as confusion. A normal ammonia level does not guarantee a normal liver, but it does not at all suggest an abnormal one.