A 25 year old asymptomatic woman has persistently elevated alkaline phosphatase for 7 years.
The ALP is 310-330 U/L (normal 35-110).
5 years ago she saw "Liver Specialist." Unremarkable investigations, including an abdominal Ultrasound.
After investigations, she was reassured that this is a part of growing. However, she continued to have it monitored at yearly intervals and it remains persistently elevated at 3 times of normal level.
Qusetions:
When is elevated alkaline phosphatase "Physiological?"
What is the cut of age after which elevated ALP becomes a concern?
Would you investigate her further. If yes, what investigation(s) you will order next?

When is elevated alkaline phosphatase "Physiological?"
Small elevation of ALP is physiological during Puberty, Pregnancy (some times) and with use of Oral Contraceptives (Ergosterol).
What is the cut of age after which elevated ALP becomes a concern?
Couldn't find a specific cut of age but believe to be the age of maturity i.e., after puberty .
Would you investigate her further. If yes, what investigation(s) you will order next?
The only investigation I did was to Fractionate ALP and the results were as follows:
Total ALP : 251 (N: 35-110)
Intestinal Isoenzyme: Increased
Placental Isoenzyme: Not Increased
Bone Isoenzyme: Slightly Increased
Hepatobiliary I Isoenzyme: Normal
Hepatobiliary II Isoenzyme: Not Detected
Conclusion: Above ALP fractionation suggest
BENIGN FAMILIAL HYPERPHOSPHATASEMIA
This is a rare familial benign persistent increase in total ALP in the absence of any known disease. It is a autosomal recessive disorder. The increase in ALP in this disorder is usually of Intestinal Origin.