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Influence of the Sample Matrix on the Stability of ß-CTX at Room Temperature for 24 and 48 Hours by Giuseppe Lippi, Giorgio Brocco, Gian Luca Salvagno, Martina Montagnana, Gian Cesare Guidi, Heinrich Schmidt-Gayk

The measurement of β-C-telopeptides of type I collagen (β-CTX) reflects the rate of bone resorption in a variety of metabolic bone disorders and it is increasingly used to assist diagnosis and follow-up of these pathologies. Since preanalytical biases in the results of this marker can decrease its clinical usefulness, specific stability studies should be developed to prevent that inconsistent results of laboratory testing might affect patient health and waste economical resources. Three blood samples were simultaneously collected without venous stasis into evacuated tubes containing no additives, K2 EDTA or lithium heparin, from 23 out-patients referred to our phlebotomy service for routine laboratory testing. After centrifugation and separation of the specimens, a first aliquot was immediately analyzed, whereas a second and third aliquot was processed after a 24- and 48-hour storage at room temperature (21 °C). β-CTX was assayed on the automated electrochemiluminescence analyzer E170. A modest and clinically irrelevant underestimation was observed in lithium heparin plasma when compared with either K2 EDTA (-7.1%; 95% C.I. -2.0 to –12.3%; p<0.001) or serum (-7.8%; 95% C.I. -3.2 to –12.4%; p<0.001), but not between serum and K2 EDTA (+0.8%, 95% C.I. -5.3 to +6.9%; p=0.260). Storage at room temperature in K2 EDTA plasma intro- duced a modest and clinically negligible decay in immunoreactivity (-4.4% and –5.7% at 24 and 48 hours, respec- tively), whereas storage at room temperature in both serum (-17.6% and –28.6% at 24 and 48 hours, respectively) and lithium heparin plasma (-29.1% and –44.0% at 24 and 48 hours, respectively) was associated with a substan- tial decay and a larger inter-individual variability in the measurable concentration of the analyte. In conclusion, the results of our investigation demonstrate that EDTA plasma is the most suitable sample matrix for the storage of β-CTX at room temperature after centrifugation.

DOI: Clin. Lab. 2007;53:455-459