Urine opiate screening: false-positive result with levofloxacin

Abstract

A 96-year-old woman with moderate to severe dementia was admitted in acute delirium. According to her next of kin, the patient had been reporting generalized weakness for the last few days, and her appetite had decreased. The day before admission, she began having visual and auditory hallucinations.At the time of admission, the patient was delirious and in moderate respiratory distress, with rapid shallow breathing and an oxygen saturation level of 88% on room air. Bilateral basilar crackles on inspiration and right-sided rhonchi were heard on auscultation. Her blood pressure was 140/75 mm Hg, her heart rate was 110 beats/min with a normal sinus rhythm, and her temperature was 37.2°C. The initial results of imaging and laboratory investigation were all normal, including a computed tomography scan of the head, chest radiographs, complete blood count with differential count, thyroid function tests, and serum levels of electrolytes, liver enzymes, amylase, lipase, cardiac enzymes, vitamin B 12 , erythrocyte folate, iron, ammonia and alcohol. The results of her blood gas tests were normal except for a partial pressure of oxygen of 60. The results of Gram staining and culture of blood, urine and sputum samples were negative for bacteria. The results of urine toxicology screening were negative for opiates and benzodiazepines. Twelve-lead electrocardiography did not show evidence of acute coronary syndrome or arrhythmias. Empirical treatment with broad-spectrum antibiotics, including piperacillintazobactam and vancomycin, was started for suspected aspiration pneumonia.Three days later, the patient's mental status and respiratory distress were worse. Levofloxacin was added to the treatment to provide coverage for atypical bacteria. A neurology consultation was obtained to rule out a neurologic cause for the patient's worsening mental status. Magnetic resonance imaging of the brain and electroencephalography were done, but neither showed acute neurologic pathology. We diagnosed metabolic encephalopathy secondary to underlying pneumonia.According to social services, the patient owned a home where she and a relative had been living together for several years. The patient had been receiving nursing care and other services in her home. Home health care staff had suspected physical abuse of the patient, and as a result, the court had appointed a lawyer as the patient's legal guardian. Given the change in the patient's mental status and upon learning about the alleged physical abuse, we were concerned about possible foul play and repeated the urine toxicology screen. To our surprise, the results were positive for opiates. A system-wide investigation was undertaken to find the possible source of the opiates. No evidence was found that an opiate-containing medication had been administered to the patient since the time of admission, and the nursing staff ruled out medication error.While searching the literature for information on possible false-positive urine screens for opiates, we found an article by Baden and colleagues, 1 whi...