Placental Alkaline Phosphatase (PLAP)

Immunology

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Description

The main application of all tumour markers is monitoring for relapse or progression. Use as a diagnostic aid requires care and knowledge of the test limitations. Opportunistic screening is discouraged. Placental alkaline phosphatase (PLAP), in association with AFP and hCG, is of value in the diagnosis and monitoring of gonadal and extragonadal germ cell tumours [1,2]. Elevated levels of this marker are seen in 55% of seminoma and combined tumour and 60% of dysgerminoma. Levels are not usually elevated in teratomata. Elevated levels may also be seen in some epithelial carcinomas of the ovary, although PLAP does not contribute greatly to the management of this malignancy and the specificity is such that it offers no advantage over CA125 [1]. PLAP has a biological half-life of less than three days, therefore this marker is of value in the monitoring of post primary treatment response and will be of particular value in patients with Stage I disease being managed by a surveillance only regimen [1]. PLAP levels in the CSF can be considered as diagnostic for pineal germinoma [1,3].

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Indications

Monitoring and diagnosis (with AFP and BHCG) of germ cell tumours.

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Sample Type

2mL Serum (Gel 5mL Yellow tube ), or 1mL CSF. Store at +4C for up to 72hrs otherwise store frozen at -20C. Requests from outside Sheffield: Transport at ambient temperature via Royal Mail or Courier.

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Reference Range

Serum: < 0.5 U/L (Non-smokers).
CSF: < 0.3 U/L.
Levels up to 1.5 U/L may be seen in moderate (one pack per day) cigarette smokers and somewhat higher levels in heavy smokers. Reference ranges established by in-house validation of the manufacturers information.

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Turnaround Time

Within 5 days

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Testing Frequency

Weekly

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External Notes

Tumour Markers are not diagnostic and are of most use in monitoring response to treatment and early detection of relapse. Normal values do NOT exclude malignancy.

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References

PRU handbook of Clinical Immunochemistry. 9th Edition. 2007. [Ref 1]Ulbright TM. Germ cell tumors of the gonads: a selective review emphasizing problems in differential diagnosis, newly appreciated, and controversial issues. Mod Pathol. 2005.18(Suppl 2):S61-79. Koshida K, et al. Significance of placental alkaline phosphatase (PLAP) in the monitoring of patients with seminoma. Br J Urol. 1996. 77(1):138-142. [Ref 2].=Shinoda J, et al. Placental alkaline phosphatase as a marker of primary intercranial germinoma. J Neurosurgery. 1988. 68(5):710-720. [Ref 3]

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