The method of thawing a frozen sample in the coagulation lab has a significant effect on testing results. It is imperative that the samples be thawed properly. The preferred method is thawing for 3-5 minutes in a circulating water bath. The thawing time of 3-5 minutes is based on a 1.0 mL vial and may need to be increased based on the size of the sample. Always ensure the samples are left in the water bath until completely thawed, but not longer. “Sample integrity may be compromised if samples are either not completely thawed or if maintained too long at 37℃.”[1] Incomplete thawing may not allow some factors to come into the solution, resulting in potential  falsely decreased values. Once the samples are thawed, it is important that they be adequately mixed before testing.

When using a water bath to thaw coagulation samples, always ensure the temperature is 37℃.  Temperatures higher than 37℃ could affect the coagulation factors in the samples, causing inaccurate test results.

Use of a 37℃ water bath is recommended over the use of heat block.  A water bath will thaw the plasma rapidly and evenly, unlike a heat block where the heat is concentrated. “Water baths provide a larger surface area so you can heat your samples within a shorter period of time. And since water baths can store a substantial amount of heat, there is very little risk of temperature fluctuations – even if you are heating multiple samples at the same time.” [2] The heat block provides a direct source of heat to the sample that could compromise the coagulation factors.

[1] Favaloro, Emmanuel J, et al. “Pre-Analytical Variables in Coagulation Testing Associated with Diagnostic Errors in Hemostasis.” Laboratory Medicine, vol. 43, no. 2, 1 Feb. 2012, doi:https://doi.org/10.1309/LM749BQETKYPYPVM.

[2]“WATER BATH OR HEAT BLOCKS (DRY BATH) – WHAT WINS?” BT Lab Systems, 31 Jan. 2018, blog.btlabsystems.com/blog/heat-block-or-waterbath.