Aim: In this study, we compared 3 different clot-activator gel tubes to a glass reference tube and evaluated the effect of storage time on 30 different biochemical analytes.

Material and Methods: Blood samples were collected in 4 types of tubes: an additive- and gel-free glass tube and three different clot-activator tubes containing gel (Samplix, Vacuette, and Vacutainer). In addition to comparison with the glass tube, stability analyses were performed in Samplix, Vacuette, and Vacutainer tubes after storage for 48 hours at +4°C.

Results: Clinically important differences were found for sodium (-0.29, bias), potassium (2.35) and magnesium (2.78) in Samplix; for sodium (-0.27), potassium (2.82), lactate dehydrogenase (4.47) and magnesium (2.46) in Vacuette; and for calcium (-1.56), chloride (0.66), potassium (3.54), lactate dehydrogenase (9.11) and sodium (0.38) in Vacutainer. At the end of the 48 hours, analytes that demonstrated instability were chloride (1.01), potassium (2.69), sodium (0.54), and total protein (1.95) in Samplix; chloride (1.11), potassium (2.06), and sodium (0.84) in Vacuette; and calcium (1.28), chloride (0.64), free T3 (-8.87), glucose (2.76), potassium (2.19), sodium (0.65), and total protein (2.15) in Vacutainer.

Conclusion: Various blood collection tubes (BCTs) with different contents may cause clinically important differences in test results. Therefore, each laboratory should verify the reference range transfer or create its own reference range before using a new BCT. It should also be noted that all clinical chemistry or immunological test analytes may not remain stable in BCTs up to 48 hours.