99: biliary “isoenzyme” of alkaline phosphatase (bi-ap)

Cholestasis lead to the appearance of a new farm of AP in the circulation. There is evidence that this chalestatic “isoenzyme” is a complex of several components (parts of liver cell mambrare, immunoglobulins, LP-X) containing the AP-isoenzyme from liver. The literature shews different rates of BI-AP activities in cholestasis. In healthy controls it had never been detected. With a modification of our previously reported HPLC-msthod (Clin Chem 1986; 32:816) far separating AP-isoenzymes we were able to standardize a sensitive and simple method for the detection of BI-AP. Method:Column equilibration in the same mamer. Sample volume 400μl. Two step salt gradient: 10 min 175 mmol/L LiCl, followed 5 min a linear increasing LiCl-cancentration until 500 mmol/L was reached. Automation was obtained by mixing the column effluent with substrate (4-methyl-umbelliferyl-phosphate, final concentration 5 mmol/ L). For detection a fluorescence detector was used. Results: It was possible to detect BI-AP in 30 healthy controls (newborns-adults), it accounted far 1-3% of the total serum AP-activity. 13 out of 20 sera from CF-patients showed an elevated activity (5-30%). Only 8 out of the 13 cases showed elevated levels of AP,GGT,GOT,GPT,3 of bilirubin and 10 of serum bile acids. We therefore conclude that measurement of BI-AP is a highly sensitive test far the early diagnosis of cholestasis in CF.