A measurement result is complete only when accompanied by a quantitative statement of its uncertainty. The uncertainty is required in order to decide if the result is adequate for its intended purpose and to ascertain if it is consistent with other similar results.  The aim of this study is to calculate measurement uncertainty of digoxin parameter by using internal and external quality control data and to compare these calculated measurement uncertainties with CLIA and RILIBAK’s total error % (TEa%) value.In the calculation of measurement uncertainty, six step “uncertainty calculation model, that is defined in Nordest guide which is based on European Accreditation Guideline / 12 /. European Tecnical Report: 1 / 3 and ISO / DTS 21748 Guideline /8/ was used. Last six months internal and external datas were used for calculations.TEa % values for Digoxin was 9,33. This value was not higher than TEa % value of RILIBAK (TEa%30) and CLIA (TEa%20).Drug analysis are important for follow-up of patients so their correct measurements are critical. However as far as our knowledge measurement uncertainity of drugs were not common Laboratories should use same guideline for standardization of measurement uncertainty and gave results lower than TEa% thats measurement uncertainty is calculated according to the same guideline. Moreover, labratories should report patient’s result with the measurement uncertainty values to clinicians.