Although many of us experience periods of anxiety, depression or self-doubt, these instances can't really be attributed to the person having low self-esteem unless they are linked together through a prolonged period of negativity and zero personal confidence.  Low self-esteem is instead a problem which exhibits itself through shyness, the expression of negative thoughts towards oneself, a feeling of worthlessness or uneasiness in one's own body, and extended periods of depression and anxiety.

The problem with diagnosing low self-esteem is that people react differently - one person may withdraw from society and become timid and depressed, whilst another may turn to alcohol and drugs to give them an escape or even to encourage feelings of confidence in social situations.  The key here is self-worth - those who believe they are of little value may act recklessly with their health or personal safety, or they may instead decide that they do not want to interact with other people for fear of being rejected or ridiculed.  If you find yourself behaving in this way, or those around you start to act in this way, it may be an indication of low self-esteem or another related psychological problem.