Effect of renal maturation on the clearance of technetium-99m mercaptoacetyltriglycine

To investigate the effect of growth and maturation on the global kidney clearance of technetium-99m mercaptoacetyltriglycine (^99mTc-MAG3), we investigated 509 children who attended for^99mTc-MAG3 renography in our department. In order to estimate the normal maturation of the kidney, only children who were classified as “normal” using diagnostic 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^99mTc-MAG3 thoughout childhood and into adolescence (mean clearance value below 2 month 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 (mean value <0.2 years: 208 ml/min/1.73 m²) to a plateau at the end of the first year of life (mean value >2 years: 303 ml/min/1.73 m²). Maturation of the kidney as defined by the normalised clearance of^99mTc-MAG3 is therefore complete by the end of the 1st year of life, after which any change in non-corrected clearance values may be attributed to growth. To investigate the appropriate normalisation factor for^99mTc-MAG3 clearance in children, clearance values were compared to height, weight and BSA. The relationships were described using a linear model; the correlation coefficients demonstrated that BSA has the highest strength of relationship with^99mTc-MAG3 clearance. Body surface area may be used over 1 year of age to normalise the clearance values of^99mTc-MAG3 Surprisingly, when clearance values are normalised to BSA, 68% of the mature clearance value is achieved at the age of <2 months of life.