EFFECT OF PHLEBOTOMY TECHNIQUE ON SERUM BICARBONATE VALUES

Objectives: To determine whether the following phlebotomy technique fa ctors result in spuriously low serum bicarbonate values: 1) small need le size, 2) prolonged tourniquet time, and 3) underfilling of Vacutain er tubes, Methods: Thirty-eight healthy young adult student volunteers from Brown University (mean age = 22 years) were randomly assigned to 1 of 2 (24-ga or 20-ga) IV needle size groups, With a tourniquet appl ied, the subjects had blood sampled initially and then at 3 intervals 1 minute apart. In addition, the initial blood sample was separated in to four 4-mL Vacutainer tubes in blood volumes of 0.5, 1, 2, and 3 mt. Serum bicarbonate values (mmol/L) were compared using these technique s, Results: 1) Small needle size did not affect serum bicarbonate valu es (p > 0.60); 2) prolonged tourniquet time resulted in a statisticall y significant serum bicarbonate elevation (32.0, 32.5, 33.8, and 33.6, respectively; p < 0.01); and 3) underfilling of Vacutainer tubes resu lted in significantly lower serum bicarbonate values for all 4 Vacutai ner blood volume groups (21.4, 23.0, 25.0, and 26.2, respectively; p < 0.001). Conclusions: Small needle size does not affect serum bicarbon ate values, Prolonged tourniquet time results in a statistically signi ficant elevation of serum bicarbonate, although this elevation may not be clinically meaningful. Underfilling of Vacutainer tubes significan tly influences the accuracy of serum bicarbonate values.