Blood ammonia determination in cirrhosis

liver411

HEPATOLOGY
November 2003 . Volume 38 . Number 5


Hepatology Elsewhere

Blood ammonia determination in cirrhosis: Still confusing after all these
years?

Cihan Yurdaydin, M.D. [MEDLINE LOOKUP]
Gastroenterology Section, University of Ankara Medical School, Cebeci Tip
Fakultesi Hastanesi, Ankara, Turkey

   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  .001), venous total ammonia (rs = 0.56, P
.001), arterial partial pressure of ammonia (rs = 0.55, P  .001), and venous
partial pressure of ammonia (rs = 0.52, P  .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.
Background/Aims: To compare venous, arterial and partial pressure of ammonia
(pNH3) in 27 consecutive cirrhotics with hepatic encephalopathy, 15
cirrhotics without hepatic encephalopathy and nine controls; to reevaluate
all parameters after the improvement of encephalopathy.
Methods: Patients were studied by clinical examination and psychometric
testing. pNH3 was calculated from arterial ammonia and pH.
Results: In patients with encephalopathy, each form of ammonia was higher
than in both controls and patients without encephalopathy. The correlation
with the severity of hepatic encephalopathy was similar for venous (r=0.72),
arterial ammonia (r=0.76) and pNH3 (r=0.75). The sensitivity and specificity
of each variable in correctly classifying the patients as having or not
having hepatic encephalopathy was also similar. Each form of ammonia
decreased after the resolution or amelioration of symptoms. However, even in
the 17 patients with complete resolution of hepatic encephalopathy, all
three ammonia determinations resulted unchanged or increased in some
patients.
Conclusions: Despite the significant correlation between pNH3 and hepatic
encephalopathy, our study suggests that neither pNH3 nor arterial ammonia
are, from a clinical point of view, more useful than venous ammonia: all
three determinations being limited both for the diagnosis of hepatic
encephalopathy and for the clinical management of the patients.

   Publishing and Reprint Information
(1) Ong JP, Aggarwal A, Krieger D, Easley KA, Karafa MT, Van Lente F,
Arroliga AC, Mullen KD. Correlation between ammonia levels and the severity
of hepatic encephalopathy. Am J Med 2003;114:188-193. (Reprinted with
permission from Excerpta Medica, Inc.)

(2) 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 Hepatol 2003;38:441-446. (Reprinted with
permission from the European Association for Study of the Liver.)