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PTD - 157

Test Directory -  Alkaline Phosphatase Isoenzymes


ALP isoenzymes

Clinical Indications

Investigation of suspected transient hyperphosphatasaemia of childhood. This may occur in some younger adults.

Abnormalities in liver function tests may occur during normal pregnancy (probably due to increased level of oestrogens) and levels of gamma-GT and alkaline phosphatase (ALP) rise in late pregnancy; the latter mainly due to placental (heat-stable) ALP. The most pronounced change is a tendency towards cholestasis in the last trimester and in a small percentage of women symptoms of jaundice/pruritus develop (intrahepatic cholestasis of pregnancy); serum bile acids may be useful and very occasionally, it may be necessary to determine whether a raised ALP level is of placental or liver origin.

In other patients, isoenzyme analysis may, rarely, be useful to investigate the origin of an unexplained elevated alkaline phosphatase level. To help differentiate whether liver or bone origin a gamma-GT is automatically added to samples with a raised alkaline phosphatase >160 IU/L with total bilirubin <25 umol/L and ALT <60 IU/L.

Request Form

Combined Pathology Blood form (Yellow/Black)


Referral test: Analysed by Biochemistry, King's College Hospital if specific criteria met.

Specific Criteria

Investigation of unexplained elevated alkaline phosphatase in childhood. Differentiation of placental alkaline phosphatase from liver in suspected intrahepatic cholestasis of pregnancy. Other requests must be agreed with Consultant Biochemist.

  Patient Preparation     None required

Turnaround Time

Same day (obstetric), 1 month (other).




2 ml


Yellow top (SST) tube or

paediatric orange top (lithium-heparin)

Causes for Rejection

Normal alkaline phosphatase level.

Lab. Handling

Processing: Aliquot (MPA) and store at 4C in separating fridge (CB39). Referral:  APISO and send or NOAPI and save in separating freezer (CB40) at -20C, saved frozen rack.

Version 1.0 / April 2014                                                                                                            Approved by: Consultant Biochemist