Experimental Investigation About Impact of Radioactivity on Blood Aminoacid Concentration Measured Through LC-MS / MS Method

Background: In order to avoid complications in congenital metabolic disorders, blood amino acid measurement should be done with LC-MS/MS, which is relatively cheap, reliable and reference method. The concentration of these tests can be affected by many molecules found in the blood matrix. It is not known how radionuclide molecules affect blood amino acid levels in metabolic disorders. The aim of this article is to investigate the effect of interference of Tc99m radionuclide radioactivities on amino acids measured by LC-MS/MS. Material and Methods: 50 μL of the level 2 amino acid control solution was taken and 10 μL of Tc99m solution was added to perform the interference study. Supernatant was measured through LC- MS/MS instrument. Measurement of supernatant solution was repeated for 1 hour. Results: False negative results were obtained between (–)0,2% and (-)100% in blood concentrations of norvaline, sarcosine, phenylalanine, alanine, threonine, alloisoleucine, isoleucine, methionine, tyrosine, leucine, 1-methylhistidine, cystathionine, 3-aminoisobutyric acid, carnosine, valine, glutamine, orthophospho-1-serine, glycine, gamma aminobutyric acid (GABA), 2-aminoadipic acid, and cystine. When the measurement was repeated from the control solution after 1 hour, all amino acid results were deviated from the target value in the range of (-)100% to (+)544%. Deviation from (-)138.5% to (+)170% was observed depending on the change in radioactivity in the repeated measurement from the same control solution. Conclusion: In metabolic disorders, measurement of the blood amino acid level after a scintigraphy monitorizing may cause false negative or false positive results. False negative results increase the risk of developing complications and sequel in patients. False positive results lead to unnecessary hospitalization. In order to prevent the radioactivity interference, amino acid measurements should not be performed immediately after radionuclid injection