Can you have flat affect without schizophrenia?

Yes: A "flat affect" simply refers to someone not being very emotionally responsive to others or to situations. Some people just naturally are less emotionally responsive to others. People who are abused or depressed may also show this symptom. With schizophrenia, it is one of the so-called "negative symptoms, " meaning it's something missing rather than a symptom like hallucinations or delusions.

Entirely Possible: Flat affect is defined as a severe reduction in emotional expressiveness. A person may not show the signs of normal emotion, they may speak in a monotonous voice, have diminished facial expressions, and appear extremely apathetic. It is commonly seen in severely depressed or traumatized individuals as well as in individuals diagnosed with schizophrenia.

Other things ?: Flat affect is a subjective finding. It has to be put into context of other findings. Besides schizophrenia, depression can present as a flat affect. Sometimes people just sound like they have a flat affect.