Measuring Ammonia Level in the ED

6 Sep
Literature review arguing that a single ammonia level is not sufficient to either diagnose or rule out hepatic encephalopathy in the ED:

–Stahl, 1963 – Loose correlation between ammonia levels and degree of coma
 
–Ong, 2003 – Ammonia levels measured in cirrhotic pts admitted to the hospital, regardless of initial mental status.

Ammonia levels increased with increasing levels of hepatic encephalopathy, with a statistically significant but  not clinically significant correlation coefficient.

69% of pts with no hepatic encephalopathy had an elevated ammonia level.
 
–Nicolau, 2003 – Serial ammonia levels were measured in cirrhotic pts with and without encephalopathy, and in controls.

In several pts whose mental status normalized, ammonia levels either did not decrease or actually increased at time of resolution [of encephalopathy] and at 48-hrs post-resolution.
 
–Kundra, 2005 – Ammonia levels measured in 20 pts with chronic liver disease (8 with encephalopathy) and 20 pts without liver disease.

No significant correlation between grade of encephalopathy and ammonia level.

Pts with more severe encephalopathy actually had lower mean ammonia levels than pts with milder encephalopathy. (Limitation: Small sample size)
 
Submitted by M. Smith.
 
References: Nicolao F, Efrati C, Masini A, Merli M, Attili AF, Riggio O. Role of determination of partial pressure of ammonia in cirrhotic patients with and without hepatic encephalopathy. J Hepatology 38 (2003) 441-446.; Arora S, Martin CL, Herbert M. Myth: Interpretation of a single ammonia level in patients with chronic liver disease can confirm or rule out hepatic encephalopathy. CJEM 2006;8(6):433-435.; picture
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