When the nurse reviews the laboratory results for a client who is being administered propylthiouracil, what result causes the nurse to notify the health care provider?

Propylthiouracil (PTU) is an antithyroid medication used to manage hyperthyroidism, including Graves' disease. One of its most serious adverse effects is hepatotoxicity, which can progress to fulminant liver failure. Elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are markers of hepatocellular injury, and a high ALT/AST result requires immediate notification of the healthcare provider so that PTU may be discontinued or the dose adjusted, preventing irreversible liver damage. A normal TSH level may actually reflect successful treatment bringing thyroid function toward normal and would not be a cause for concern. A slightly low potassium level may warrant monitoring and possible supplementation but is not specifically linked to PTU toxicity. A slightly low T4 level could indicate that PTU is working as intended and might prompt a dose reduction, but it does not represent the urgent safety concern that elevated liver enzymes do. Because PTU-induced hepatotoxicity carries significant morbidity and mortality, liver function tests are routinely monitored during therapy, and any elevation above normal is treated as a red flag requiring prompt provider communication.