Bone Abstracts

Objective: To investigate i) the analytic stability of PTH in venous blood specimens in serum tubes processed at different time intervals after collection compared to immediately processed blood samples collected in K2EDTA tubes, and ii) whether storage of samples in serum tubes for 5 years at −20 °C had an effect on stability of PTH.

Methods: Venous blood samples were collected from ten healthy Caucasian females. One K2EDTA tube and three serum tubes were sampled. The K2EDTA tubes were centrifuged immediately. The serum tubes were processed 30, 60, and 120 min after collection. Also, 100 serum samples obtained between September 2007 and February 2008, and stored at −20 °C were analyzed. All samples were analyzed with intact PTH immunoassay (Cobas, Roche Diagnostics).

Results: Using plasma samples processed immediately after collection in the 10 healthy subjects as gold standard, the retrieval in serum samples processed at 30 min was 91.8%. Serum processed at 60 and 120 min showed retrieval of 91.9 and 91.1%, respectively, with no time trend (P>0.84).

In serum tubes stored for 5 years, PTH values were significantly elevated compared to the reference interval (P<0.01). No significant difference between PTH from the 5-year old serum samples and matched K2EDTA tubes measured from March to April 2007 was present (P=0.58).

Conclusion: It is possible to obtain valid PTH results in serum stored for 5 years. The PTH retrieval in serum compared to plasma was acceptable, and delayed processing for up to 120 min did not affect stability.