Medical identity theft occurs when someone uses another person's health information for medical services, leading to potential financial and credit issues for the victim. To detect it, individuals should regularly review medical records and insurance statements for discrepancies, and to correct it, they must obtain their medical records, report inaccuracies to providers, and keep detailed documentation of their communications. Preventative measures include being cautious about sharing health information, shredding sensitive documents, and securely managing personal data.