Influence of Preanalytical Factors on the Immulite Intact Parathyroid Hormone Assay

Preanalytical Influences on DPC IMMULITE 2000 Intact PTH Assays of Plasma and Serum from Dialysis Patients

“…The discrepancies are not unique to reagent lot 121. We have seen similar differences with lots 114 and 115 (data not shown), as have others with lots 109 and 112 (12 ). In addition, the negative difference for SST serum compared with EDTA plasma was not a matrix effect attributable to the SST tube, as reported for other analytes on the Immulite 2000 (16 ).…”

“…The consistently higher baseline results in EDTA plasma over SST have been noted previously in more heterogeneous populations (6,12 ). Appropriately, DPC has issued EDTA-specific reference intervals (13 ).…”

“…A statistically nonsignificant increase in measured PTH in EDTA specimens has been reported after storage at room temperature (6 ). A similar but statistically significant effect has been seen in EDTA plasma collected and centrifuged at room temperature and then refrigerated (12 ). The mechanism of the effect is unclear.…”

“…Storage of SST serum samples for 3 days at room temperature decreased measured PTH in SST serum samples, an effect not seen with EDTA plasma (6 ). Results from EDTA plasma paradoxically increased after storage at 4°C (12 ). Despite evidence that PTH is more stable in EDTA-anticoagulated specimens (5-7, 9, 10 ), the manufacturer describes an instability associated with EDTAplasma samples and therefore recommends cold (2-8°C) collection, centrifugation, and storage until analysis (13 ).…”

Considerations in parathyroid hormone testing

“…Thus, two samples would be needed once again. Finally, excess EDTA in underfilled tubes can inhibit signal production in methods that use alkaline phosphatase [22]. In conclusion, excepted for the particular case of parathyroid surgery, we believe that serum should be preferred over EDTA for routine testing.…”