The caregivers of a child with a history of ear infections calls the nurse and reports that her son has just told her his urine “looks funny.” He also has a headache, and his mother reports that his eyes are puffy. Although he had a fever 2 days ago, his temperature is now down to 100 °F (37.8 °C). The nurse encourages the mother to have the child seen by the care provider because the nurse suspects the child may have: