This report was originated from the analysis of the results of a joint EURADOS-EANM project about the assessment of the external radiation dose rate to comforters and caregivers exposed to patients undergoing nuclear medical diagnostics and therapy. The compartmental model for 18F-FDG developed by Hays and Segall in 1999 was applied by EURADOS members for predicting the time activity curves (TAC) in the source organs and tissues, and the urinary excretion. Inconsistencies have been found between the TAC and the time integrated activity coefficients (TIAC) calculated by EURADOS and those published by Hays and Segall and the Committee on Medical Internal Radiation Dose (MIRD). A quality assurance in form of an intercomparison on the implemented Hays and Segall compartmental model for 18F-FDG was carried out between four institutions of EURADOS voting members to validate the model predictions. The differences in calculated TIAC between EURADOS and MIRD results reach up to a factor of 3.2 by using arithmetic mean model parameters and 3.8 by using geometric mean parameters. The inconsistencies are under investigation in contact with MIRD Committee. A suggestion of updating the compartmental model for 18F-FDG with new available data is made.