Plastic versus Glass Tubes: Effects on Analytical Performance of Selected Serum and Plasma Hormone Assays

During the last decade, plastic blood collection tubes have been progressively replacing glass tubes. Plastic tubes are not only less expensive but also safer than glass tubes, because they are less likely to break. Unfortunately, it is frequently difficult or impossible for individual laboratories to obtain comprehensive data on the equivalence of replacement plastic tubes vs their original glass counterparts. This is a particularly important issue for many endocrine assays, especially peptide hormones. These often degrade rapidly and can adsorb to a variety of surfaces (1)(2)(3)(4)(5)(6)(7). Changing from glass to plastic tubes can also be problematic for analytes that are regarded as stable. An example of the latter can be seen in therapeutic drug monitoring, where plastic tubes have been shown to influence the measured concentrations or stabilities of several drugs (8)(9)(10). Similar concerns may apply to low-molecular-weight hormones, such as steroid hormones and biogenic amines. These are increasingly assayed by HPLC, gas chromatography-mass spectrometry, or liquid chromatography-tandem mass spectrometry. It is conceivable that low-molecular-weight organic substances released by plastic tubes could interfere in some of these assays (11) and that small changes that are not detected by immunoassays would change the results of more specific methods. Finally, in certain situations, such as serial monitoring of tumor markers, even minor discrepancies between glass and plastic tubes may gain significance during changeover from one type of collection to the other.We designed the present study to give a reasonable representation of the range of analytes and analytical methodologies used in our laboratory, with particular emphasis on peptide hormones because of their known instability. We selected the following analytes: