The introduction of a new analytical analyzer into routine clinical biochemistry laboratories requires verification in order to test the analyzer's analytical features as defined by the manufacturer. The method of determining aminotransferase activity with the addition of pyridoxal phosphate (PLP) involves the verification procedure (repeatability, interlaboratory precision, measurament uncertainty), trueness checkup, stability and comparison with a method without the addition of PLP. PLP is used for those who have a deficit of PLP and to avoid a false assessment of the actual enzyme content. The aim of the study was to conduct a study on a group of patients with predictable deficit of PLP and on a group of subjects with no PLP deficit expected. Remaining blood samples were used after routine laboratory analysis of hospital patients at the Clinical Institute of Chemistry KBC Sestre milosrdnice. The results of the analytical verification showed that the methods had satisfactory repeatability, interpersonality and measurement uncertainty while their stability did not meet the eligibility criteria. By verifying the trueness and processing the results of Passing-Bablok regression and Bland-Altman analysis, there was a significant difference in measurement of enzyme activity between the methods in all the investigated groups. The PLP method measures higher values of the enzyme activity but also lower than the method without PLP. Therefore, we conclude that the results of the measurements with the addition of PLP are not comparable to the method without the addition of PLP and the results should not be published alternately. This is important to doctors because they won't be able to longitudinally track the findings at the time of transition to another method.