EFFECT OF RENAL MATURATION ON THE CLEARANCE OF TC-99M MERCAPTOACETYLTRIGLYCINE

To investigate the effect of growth and maturation on the global kidne y clearance of technetium-99m mercaptoacetyltriglycine (Tc-99m-MAG3), we investigated 509 children who attended for Tc-99m-MAG3) renography in our department. In order to estimate the normal maturation of the k idney, only children who were classified as ''normal'' using diagnosti c criteria were included in this study (n = 109). Kidney clearance was calculated using a gamma camera technique and a 20-min blood sample. There was a progressive increase in the clearance of Tc-99m-MAG3 thoug hout childhood and into adolescence (mean clearance value below 2 mont h was 31.4 ml/min, mean clearance value above 12 years was 287 ml/min) . When clearance was normalised to body surface area (BSA) a different pattern was seen, with a progressive increase from 3 weeks of age (me an value < 0.2 years: 208 ml/min/1.73 m(2)) to a plateau at the end of the first year of life (mean value > 2 years: 303 ml/min/1.73 m(2)). Maturation of the kidney as defined by the normalised clearance of Tc- 99m-MAG3 is therefore complete by the end of the 1st year of life, aft er which any change in non-corrected clearance values may be attribute d to growth. To investigate the appropriate normalisation factor for T c-99m-MAG3 clearance in children, clearance values were compared to he ight, weight and BSA. The relationships were described using a linear model; the correlation coefficients demonstrated that BSA has the high est strength of relationship with Tc-99m-MAG3 clearance. Body surface area may be used over 1 year of age to normalise the clearance values of Tc-99m-MAG3. Suprisingly, when clearance values are normalised to B SA, 68% of the mature clearance value is achieved at the age of < 2 mo nths of life.