Alkaline Phosphatase Isoenzymes
Biochemistry Overview / Directory
Purpose of the test
Alkaline phosphatase (ALP) in the circulation is a mixture of isoforms from the liver, kidney, bone and intestine. There are three genes for ALP - intestinal, placental and the liver/kidney/bone gene. The latter isoforms undergo post-translational modification with different carbohydrate sidechains being attached. In some instances it is important to be sure whether a raised plasma ALP is of liver or bone origin (e.g. malignancy, co-existing liver disease etc.). ALP isoenzymes can be resolved using isoelectric focusing into all the major forms.
In particular marked elevations of plasma ALP can be seen in children (and occasionally in adults) associated with concurrent infections. This is caused by changes in the carbohydrate sidechain structure resulting in reduced recognition at clearance receptors and a prolonged half-life - transient hyperphosphatasaemia. This produces a characteristic pattern on isoelectric focusing with a particular response to neuraminidase treatment which aids recognition. It is a benign condition and the importance of identifying it is to avoid unnecessary investigations e.g. ERCP, bone scans etc.
Sample Requirements
Serum (250 µL).
Storage and Transport
Stable at 4°C for up to one week. Send by overnight first class post.
Turnaround Time
Approximately 1-2 weeks.
Price
Price available on application - please contact adrian.turner@kch.nhs.uk. Discounts could be available for significant workloads.
Contacts
Dr Roy Sherwood
Tel: 020 3299 3726
e-mail roy.sherwood@nhs.net
References
O`ERiordan SP, Baker A, Sherwood RA (2002). Isoenzyme characterisation in isolated elevation of alkaline phosphatase following liver transplantation in children
Transplantation 74: 1030-4
Wong T, Wood F, Sherwood RA (1999) Transient hyperphosphatasaemia in an adult with pre-existing liver disease. Ann Clin Biochem 36: 516-8
