Question 36

Hemoconcentration of a venous blood sample is most often caused when the tourniquet is in place for more than 2 min.

When a tourniquet is applied for an extended period, typically more than two minutes, it can lead to hemoconcentration, which is an increase in the concentration of cells and proteins in the blood due to the reduced flow of plasma.

A) the site is prepped with povidone iodine.

Using povidone iodine for site preparation is a common practice to disinfect the skin before venipuncture. This action does not cause hemoconcentration; instead, it ensures that the site is clean and minimizes the risk of infection.

B) the tourniquet is in place for more than 2 min.

When a tourniquet remains applied for over two minutes, it can restrict venous return while allowing arterial blood flow to continue, resulting in an increased concentration of blood cells and proteins in the sample. This is the primary cause of hemoconcentration in venous blood samples.

C) the specimen is not refrigerated within 30 min.

While improper storage of blood specimens can affect the stability of certain analytes, it does not directly cause hemoconcentration. Hemoconcentration is a physiological change that occurs during specimen collection rather than during storage.

D) the needle is removed before the tourniquet.

Removing the needle before releasing the tourniquet can lead to other complications, such as hematoma formation, but it does not cause hemoconcentration. Hemoconcentration specifically results from prolonged tourniquet application, not the order of these actions.

Conclusion

The most significant factor leading to hemoconcentration in venous blood samples is the extended application of a tourniquet, as indicated in option B. All other options either do not affect hemoconcentration or relate to different aspects of blood collection and specimen handling. Understanding the effects of tourniquet duration is crucial for accurate blood analysis and patient care.