PTH Assay Change at SydPath - 16th January 2012
The
major changes are as follows:
Measurement using the
Roche Modular Analytical system.
This replaces the
Immulite analyser used for previous 15 years.
Results will be
available within 3 hours of sample arrival in laboratory.
Reference intervals
have been revised (see below).
New assay
Details
New assay is a two
site (sandwich) assay using monoclonal antibodies and electrochemiluminescent detection.
This "Intact
PTH" assay detects both PTH 1-84 and 7-84. Shows good overall correlation with PTH
1-84 assay (PTH 1-84 results ~70% of Intact PTH).
The new and old assays
give similar results within the reference interval. However the new assay runs
approximately 20% lower in samples with concentrations above the reference interval and
0.5 pmol/L higher in samples with concentrations at the low end of the measuring range.
The assay shows
improved precision compared with the previous system.
Note that within
subject-variation of PTH shows a variability of approximately +/- 40% and pre-analytical
factors (sample stability) and assay imprecision can add slightly to this.
Sample
Collection
The recommended sample
type is serum (gold top). The sample should be sent to the laboratory as soon as possible
or centrifuged within 2 hours of collection. If this is not possible a separate gold top
tube should be collected and placed on ice for transport to the laboratory.
"Add on"
requests to samples already in the laboratory are only possible up to 2 days from sample
collection.
New Reference
interval: 1.5 - 7.0 pmol/L (previously
1.0 - 7.0 pmol/L)
Note this is a general
reference interval only. Serum PTH increases with older age, and with decreasing renal
function, calcium intake and vitamin D status.
This interval has been produced with data from manufacturer's information, local studies
and published papers.
Assay Availability:
The assay is available 24/7 with results available
within 3 hours of sample arrivel in laboratory.
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