Is heparinized plasma suitable for use in routine biochemistry?

Using lithium heparin plasma and serum, we compared the values of 27 biochemical analyses performed with a Kodak Ektachem 500 analyzer. For 16 of the 27 tests, we observed statistical differences between the mean results obtained from the analysis of heparinized plasma and those obtained from the analysis of serum (Student t-test; P < .001). However, none of these differences were medically significant. When the concentration of lithium heparin was increased to three and five times normal (reflecting incomplete Vacutainer tube filling), alanine aminotransferase, amylase, aspartate aminotransferase, lipase, and potassium all exhibited some changes compared with serum. Therefore, heparin may be used to shorten the turnaround time in the routine biochemistry laboratory, but the anticoagulant tubes should be completely filled to prevent spurious intraindividual variations in serial specimen analysis.