Serum alkaline phosphatase in cystic fibrosis. Interpretation of elevated values based on electrophoretic isoenzyme analyses.

Sera from 31 of 146 patients with cystic fibrosis (CF) contained levels 
of serum alkaline phosphatase (AP) which were elevated by age-related criteria. 
Prominent liver isoenzyme bands were present after polyacrylamide gel electrophoresis of 
all 31 abnormal sera. Larger than normal amounts of bone and 
intestinal AP were not present in these sera. These findings indicate 
that liver abnormalities consistently are responsible for elevations of total AP 
in sera of patients with CF. Several causes of high liver 
AP levels in CF patients were identified: chronic hepatic congestion, drug 
hepatotoxicity, overt biliary cirrhosis, and most commonly subclinical focal biliary cirrhosis. 
