Baltaru and her colleagues evaluated plasma sRANKL levels of 15 patients with rheumatoid arthritis, who had never received corticosteroids or disease-modifying antirheumatic drugs.
Plasma sRANKL values were determined by quantitative enzyme-linked immunosorbent assay.
Methotrexate therapy significantly reduced plasma sRANKL levels in the rheumatoid arthritis patients, to a median value of 185 pg/mL.
To assess the effect of storage of samples on sRANKL and OPG stability, blood was drawn into lithium-heparin and EDTA collection tubes, allowed to stand at room temperature for 30 min, and centrifuged at 1814g for 10 min at 4 [degrees]C before the plasma was collected.
Interassay imprecision for sRANKL and OPG was established by measuring quality-control material provided in the assays (n = 16 assays).
The effects on sRANKL concentration of collecting blood into different anticoagulants, varying the time interval between collection and centrifugation, and altering storage conditions of samples are shown in Fig.
These data suggest that samples for use in sRANKL and OPG assays should be collected into EDTA.
The effects of storage for 6 weeks or 6 months after collection on sRANKL and OPG concentrations in serum/ plasma samples are summarized in Table 1.
When samples were collected into nonsiliconized plastic syringes, significant variability in sRANKL was observed compared with results obtained when siliconized tubes were used (SARSTEDT-MONOVETTE).
The variability in sRANKL concentration under different storage conditions suggests a possible explanation for previous discordant findings (5,8-11).