Standardization of DiaSorin and Roche automated third generation PTH assays with an international standard: impact on clinical populations

Background: Standardization of parathyroid hormone
(PTH) assays is a major issue, especially in hemodialyzed
(HD) patients. Two automated third generation
PTH assays (Roche Elecsys and DiaSorin Liaison) are now
available. These assays are specific for the (1-84) PTH and
do not cross-react with the (7-84) fragment, contrary to
second generation (intact) assays. We aimed to calibrate
the two methods against the WHO International PTH
Standard (IS) 95/646 to see if the two assays could provide
comparable results in a population of healthy subjects,
HD patients and patients suffering from primary hyperparathyroidism
(PHP).
Methods: We selected 79 healthy subjects and two populations
of patients presenting PTH disorders: 56 HD and 27
PHP patients. We reconstituted the IS in a pool of human
serum containing undetectable levels of 1-84 PTH and prepared
13 serum standards ranging from 0 to 2000 pg/mL.
The standards were run on the two instruments to calibrate
the assays on the IS. The different populations were
run before and after restandardization.
Results: As these kits were differently calibrated, the
results obtained after restandarization were significantly
different. Restandardization process improved concordance
between assays and, taking the analytical variability
of the two kits into account, the results could be considered
to be similar.
Conclusions: Restandardization of automated third
generation PTH assays with the WHO 1-84 PTH Standard
significantly reduces inter-method variability. Reference
ranges and raw values are totally transposable
from one method to the other in healthy subjects, but
also in diseased patients, e.g., with HD or those suffering
from PHP.