Regular article
Correlation between ammonia levels and the severity of hepatic encephalopathy

https://doi.org/10.1016/S0002-9343(02)01477-8Get rights and content

Abstract

Purpose

Because the correlation between ammonia levels and the severity of hepatic encephalopathy remains controversial, we prospectively evaluated the correlation in 121 consecutive patients with cirrhosis.

Methods

The diagnosis of hepatic encephalopathy was based on clinical criteria, and the severity of hepatic encephalopathy was based on the West Haven Criteria for grading of mental status. Arterial and venous blood samples were obtained from each patient. Four types of ammonia measurements were analyzed: arterial and venous total ammonia, and arterial and venous partial pressure of ammonia. Spearman rank correlations (rs) were calculated.

Results

Of the 121 patients, 30 (25%) had grade 0 encephalopathy (no signs or symptoms), 27 (22%) had grade 1, 23 (19%) had grade 2, 28 (23%) had grade 3, and 13 (11%) had grade 4 (the most severe signs and symptoms). Each of the four measures of ammonia increased with the severity of hepatic encephalopathy: arterial total ammonia (rs = 0.61, P ≤0.001), venous total ammonia (rs = 0.56, P ≤0.001), arterial partial pressure of ammonia (rs = 0.55, P ≤0.001), and venous partial pressure of ammonia (rs = 0.52, P ≤0.001).

Conclusion

Ammonia levels correlate with the severity of hepatic encephalopathy. Venous sampling is adequate for ammonia measurement. There appears to be no additional advantage of measuring the partial pressure of ammonia compared with total ammonia levels.

Section snippets

Patients

We recruited consecutive patients with cirrhosis who were admitted to our institution between September 1998 and December 1999. Patients were enrolled within 24 hours of admission, regardless of their mental status. A diagnosis of cirrhosis was determined by biopsy (41% [50/121] of patients) or by signs of portal hypertension, such as ascites, gastroesophageal varices, or previous variceal bleeding. We obtained informed consent from each patient or from an immediate family member if the patient

Results

Of the 153 patients whom we approached for the study, 16, including 10 with hepatic encephalopathy, refused to participate. Another 16 patients did not meet inclusion and exclusion criteria (2 did not have cirrhosis, 4 were on hemodialysis, 8 had recently been drinking alcohol, and 2 had altered mental status due to causes other than hepatic encephalopathy). The remaining 121 patients were included in the final analysis (Table 2). Their mean (± SD) age was 54 ± 10 years (range, 29 to 75 years).

Discussion

We found a strong correlation between ammonia levels and the severity of hepatic encephalopathy. To overcome some of the limitations of previous studies, we optimized the conditions under which the relation between hepatic encephalopathy and ammonia levels was examined. Ammonia measurement was performed using a newer and more reliable enzymatic method, and grading of encephalopathy was blinded to the ammonia measurements. Under these conditions, ammonia levels correlated strongly with the

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This study was supported by a research grant from the American College of Gastroenterology, Arlington, Virginia.

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