When collecting blood samples using evacuated tubes, various factors can influence the volume of blood drawn. Understanding these factors is crucial for ensuring accurate and reliable sample collection. Let’s look into three key factors that affect the drawing volume of evacuated tubes: Temperature, Altitude, and Humidity.

1.Temperature (T):

Temperature plays a significant role in the pressure of the gas inside evacuated tubes. Storing tubes at low temperatures decreases the gas pressure, resulting in an increase in draw volume. Conversely, higher temperatures can lead to reductions in draw volume, impacting the stability of certain tube additives.

2.Altitude (A):

At high altitudes, the ambient pressure is lower than at sea level. This difference affects the pressure of the residual gas inside the tube during filling, leading to a correspondingly lower draw volume. Studies have shown that draw volumes decrease by approximately 0.5 mL for every 1000 m gain in terrestrial elevation, presenting challenges such as insufficient blood volume for testing and the risk of air embolism.

3.Humidity (H):

Humidity levels can affect plastic evacuated tubes due to their higher permeability to water vapor compared to glass. Very high humidity conditions may cause water vapor migration inside the tube, potentially compromising moisture-sensitive additives. Conversely, very low humidity conditions can accelerate water vapor escape, which might compromise the accuracy of clinical results stored under such conditions.