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.