Is it OK to take blood tests from a patients peripheral cannula?

An informative study over at IV Team looks at the question: Can we obtain an accurate blood test drawn from an existing peripheral IV cannula?

Blood was drawn from patients with existing IV cannulas. If they had an infusion in progress, it was halted and flushed with 0.9% saline.
After 2 minutes 2 mls was drawn and discarded, followed by the specimen collection.
Immediately a venipuncture was performed on the opposite arm and both samples were analysed for haematology, biochem, Coags and venous blood gas.

The authors of the study concluded:

Blood samples extracted from a peripheral catheter with or without drug infusions are valid for the analysis of hematology, biochemistry, and coagulation parameters but not for venous blood gases. Nurses should know the benefits of using an existing peripheral catheter for drawing blood samples for laboratory analysis even when infusing commonly used drugs. Emergency nurses should consider collecting blood specimens from a venous access device regardless of the type of drug infusions administered, because it is a safe, simple, and fast technique, which is time efficient when treating patients with limited venous access sites. This procedure reduces patient discomfort and the risk of complications related to venipunctures.

Reference: Venipuncture from existing peripheral IV catheter in the emergency department