Point-of-care analysis of blood ammonia with a gas-phase sensor
Abstract
Elevated blood ammonia (hyperammonemia) may cause delirium, brain damage, and even death. Effective treatments exist but preventing permanent neurological sequelae requires rapid, accurate, and serial measurements of blood ammonia. Standard methods require volumes of 1 to 3 ml, centrifugation to isolate plasma, and a turn-around time of two hours. Collection, handling, and processing requirements mean that community clinics, particularly those in low resource settings, cannot provide reliable measurements. We describe a method to measure ammonia from small-volume whole blood samples in two minutes. The method alkalizes blood to release gas phase ammonia for detection by a fuel cell. When an inexpensive first-generation instrument designed for 100 µl of blood was tested on adults and children in a clinical study, the method showed a strong correlation (R2 = 0.97) with an academic clinical laboratory for plasma ammonia concentrations up to 500 µM (16 times higher than the upper limit of normal). A second-generation hand-held instrument designed for 10-20 µl of blood showed a near perfect correlation (R2 = 0.99) with healthy donor blood samples containing known amounts of added ammonium chloride up to 1000 µM. Our method can enabl...Continue Reading
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