Placental alkaline phosphatase (PLAP)
|Category||Biochemistry >> Oncology|
Alkaline phosphatases (ALP) are membrane anchored dimeric enzymes. Specific phospholipases can cleave membrane bound ALP and produce free ALP in the serum. ALP consists of a family of four isoenzymes: (1) placental ALP (PLAP) (2) germ cell ALP (PLAP-like), (3) intestinal ALP (IAP), and (4) nonspecific tissue ALP (TNAP, also known as liver/bone/kidney ALP). The PLAP and PLAP-like enzymes share 98 % homology in their amino acid sequence and are both recognised by the PLAP assay. PLAP is synthesised in the placental syncytiotrophoblast starting after the 12th week of pregnancy. The PLAP-like enzyme is primarily synthesised in the testis, cervix and thymus. In healthy non-smoking adults, PLAP/PLAP-like enzyme activity represents less than 1 % of all serum ALP. Smoking causes elevation of the serum concentrations of the PLAP-like enzyme, limiting the value of PLAP-like enzyme as a tumour marker in smokers. Serum concentrations of PLAP-like enzyme return to the normal range after 1-2 months of smoking cessation. Ectopic expression of PLAP has been associated with cancer of the ovary, testis, lung and colorectal tract. The highest frequency of serum elevations of PLAP and PLAP-like enzyme are found in patients with ovarian (25 %-65.5 %) and testicular neoplasms 22 %-89 % (20-90 %).
Germ cell tumour
Diagnosis:PLAP may be helpful as an adjunctive test in the clinical work-up of GCT. It is most frequently raised in seminomas.
|Sample & container required||SST (gold top) preferred, serum (red top) accepted|
|Sample volume||1 mL|
|Transport storage||Store at 2-8°C and send by first class post. If sample receipt will be delayed by >3 days, store samples at -20°C and send frozen|
|Turnaround time||4 weeks|
Samples with total ALP activity >800 IU/L may react non-specifically in the PLAP assay.
Innotest enzyme immunoassay
Please note that this assay is not fully validated for the analysis of CSF. Please contact the Duty Biochemist on 020 331 30348 to discuss CSF PLAP requests. Samples should be in a universal container and as fresh as possible. Avoid repeated freeze/thaw cycles.