Carbon nanotubes (CNT) cytotoxicity is frequently investigated using in vitro classical toxicology assays. However these cellular tests, usually based on the use of colorimetric or fluorimetric dyes, were designed for chemicals and may not be suitable to nano-sized materials. Indeed, due to their unique physico-chemical properties CNT can interfere with the assays and bias the results. To get accurate data and draw reliable conclusions, these artifacts should be carefully taken into account. The aim of this study was to evaluate qualitatively and quantitatively the interferences occurring between CNT and the commonly used lactate dehydrogenase (LDH) assay. Experiments in cell free conditions were performed and it was clearly demonstrated that artifacts occurred. They were due to the intrinsic absorbance of CNT on one hand and to the adsorption of LDH at the CNT surface on the other hand. The adsorption of LDH on CNT was modeled and was found to fit the Langmuir model. The Kads and neq constants were defined, allowing the correction of results obtained from cellular experiments to get more accurate data and lead to proper conclusions on the cytotoxicity of CNT.