Osteocalcin concentrations in plasma prepared with different anticoagulants

Area of Science:

• Biochemistry
• Clinical Chemistry
• Endocrinology

Background:

• Osteocalcin is a key biomarker in bone metabolism.
• Accurate measurement of osteocalcin is crucial for clinical diagnostics.
• The influence of anticoagulants on plasma analyte stability is a known concern.

Purpose of the Study:

• To evaluate the impact of various anticoagulants on plasma osteocalcin concentrations.
• To compare plasma osteocalcin levels obtained with different anticoagulants against serum values.
• To assess the stability of osteocalcin in plasma and serum under storage conditions.

Main Methods:

• Plasma and serum samples were collected using different anticoagulants: oxalate/fluoride, sodium citrate, and lithium heparin.
• Osteocalcin concentrations were measured using enzyme immunoassay and radioimmunoassay.
• Sample stability was tested after two freeze/thaw cycles at -20°C.
• Correlation analysis was performed between serum and plasma osteocalcin levels.

Main Results:

• Oxalate/fluoride anticoagulant significantly reduced plasma osteocalcin to 37.3% of serum values, likely due to increased hemolysis.
• Sodium citrate (0.105 mol/L) and lithium heparin yielded plasma osteocalcin levels of 92.4% and 83.6% of serum values, respectively.
• Osteocalcin concentrations remained relatively stable in both plasma and serum after two freeze/thaw cycles.
• A good correlation (r² = 0.831) was observed between serum and lithium heparin plasma osteocalcin, though serum values were sometimes 2-3 times higher.

Conclusions:

• The choice of anticoagulant critically affects plasma osteocalcin measurements.
• Oxalate/fluoride is not recommended for plasma osteocalcin analysis due to significant underestimation.
• Lithium heparin and sodium citrate are more suitable anticoagulants for plasma osteocalcin determination.
• Standardization of blood collection procedures is essential for reliable osteocalcin biomarker assessment.