Micronucleus and fragility test as indicators of damage response in human lymphocytes after I-131 therapy

To estimate the absorbed dose received by patients who underwent 131I therapy, a modified compartmental model of the International Commission on Radiological Protection (ICRP) was used. The activity in plasma and micronucleus (MN) frequency (MN test) were measured before and after therapy. To evaluate whether a correlation exists between lymphocytes and absorbed dose, a colorimetric test, based on the tetrazolium salt 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT test), was used. Twenty patients who underwent 131I therapy were studied. Activity was measured in plasma, and isolated lymphocytes were collected to perform the MN and MTT tests. The mean MN frequency observed in unexposed patient lymphocytes was comparable with that of healthy subjects. 131I therapy induces a small increase in MN, and a good correlation with the bone marrow absorbed dose was obtained (P = 0.040). A consistent decrease in phytostimulation observed after therapy (MTT test) correlated significantly with bone marrow absorbed dose (P = 0.0085). The MTT test appears to be more reliable than the MN test for evaluating lymphocyte damage induced by 131I therapy.