Comparison of laboratory values obtained by means of routine venipuncture versus peripheral intravenous catheter after a normal saline solution bolus

This study compares selected laboratory values of blood samples obtained by means of venipuncture and by means of a peripheral intravenous catheter after a normal saline solution bolus.

In this prospective experimental study, each participant served as his or her own control. Hospital employees volunteered in the emergency department of a tertiary-care teaching hospital. Participants had a peripheral catheter placed in one upper extremity and received a 200-mL bolus of normal saline solution during a 10-minute period. After a 2-minute wait period, a 12-mL aspirate was withdrawn directly from the saline solution lock. A second 12-mL aspirate was also obtained. Concurrently, venipuncture was performed on the other upper extremity. All 3 samples were analyzed for CBC, electrolytes, blood urea nitrogen, creatinine, glucose, liver function tests, and prothrombin time/international normalized ratio (PT/INR). Limits of agreement analysis based on the definition of clinical equivalence, as determined by surveying residency-trained and board-certified emergency physicians, was used to compare the results of catheter aspirates with those of venipuncture aspirates.

Thirty-three volunteers participated. When comparing venipuncture versus first aspirate, 16 of the 19 laboratory tests evaluated had 99% agreement intervals that were within the predetermined definition of clinical equivalence. Potassium, bicarbonate, and glucose did not demonstrate clinical equivalence, and this difference persisted after a 12-mL discard volume.

This study supports the use of blood samples obtained by means of aspiration from a peripheral catheter when testing for CBC, blood urea nitrogen, creatinine, liver function tests, and PT/INR in healthy-appearing patients. Catheter aspiration, when testing for electrolytes and glucose, may be reasonable in a more select group of patients.