ALP exists in several isoenzyme forms produced by different tissues. When total ALP is elevated, isoenzyme analysis helps identify whether the source is the liver, bones, intestine, or other tissues, which can significantly narrow the diagnostic possibilities.
This test is ordered when total ALP is elevated and the clinical context doesn't clearly point to a liver or bone source — for example, when other liver tests are normal but ALP is high, or when bone disease is suspected. Results help guide further evaluation such as liver imaging, bone scans, or specialist referral. Sample type is serum.