I am not a psychologist, but my non-medical opinion is that a person is either born with a cognitive disorder (I think the current preferred term is intellectual disability although I think mental retardation is actually more apt) which would be manifested in daily living deficits and poor performance in school at least before puberty. So if this is the first IQ score of 58 and the test was done when someone was in their 30's, 40's, 50's or later, and there is no evidence of brain damage, that it could be that you didn't try hard enough on your test. But a good test includes ways of finding that out.

I talked to a couple one time. The wife did all the talking. Said her husband had the mind of a child and he had always been like that. Said he wet the bed. I asked why did she marry him and why did she sleep in the same bed. She said you can't help who you fall in love with. Watched them walk to the parking lot and this man with a mind of a child got behind the steering wheel and drove away with her in the passenger seat. He probably also had an IQ test that scored under 58 but he was denied.