We gratefully acknowledge the diligent employees of the Chemistry laboratory at San Francisco General Hospital.

consistent with left lower lobe pneumonia vs atelectasis, lumbar puncture revealed no evidence of infection, and all culture studies remained without growth. Working diagnoses included postictal state, sepsis, and possible pneumonia. The patient was admitted and treated with anticonvulsive medications, intravenous fluids, and broad-spectrum antibiotics. The next day, he was afebrile with a normal white blood cell count. His creatinine was now elevated at 2.5 mg/ dL, up from 1.1 mg/dL on admission (reference range, 0.71.3 mg/dL). Creatine kinase was 11 600 U/L (reference range, 38-174 U/mL); peak levels were observed 2 days later at 82 800 U/mL. A diagnosis of acute renal failure due to rhabdomyolysis was made. With aggressive fluid treatment, serum creatinine normalized; and the patient was discharged in good condition to home on hospital day 5. Our patient suffered a chain of clinical events that led from a bout of acute pneumonia to generalized seizure activity to rhabdomyolysis with transient renal failure. The case came to our attention because of a dramatically elevated serum lactate level upon presentation in the ED that dropped by 80% from its peak level in a little more than 2 hours. The clinicians who had considered sepsis a possible diagnosis in this patient based on fever, tachycardia, leukocytosis, and hyperlactatemia on presentation were puzzled by the rapid and dramatic drop in serum lactate. The concern was enough to generate a formal request for the laboratory to verify the validity of the results. As serum lactate levels are increasingly used in ED and intensive care settings as a biomarker for severe sepsis diagnosis and prognosis [1] ,w e believe that this case is helpful in illustrating the significance but also the limitations of a markedly elevated serum lactate concentration in an acutely ill patient. Lactate is constantly produced throughout the body and released into the circulation, with the majority being produced by skeletal muscle tissue, brain, skin, and red blood cells, whereas liver and kidneys are net consumers of lactate [2]. Normally, lactate production and consumption are well