Objective: To perform a cross-sectional comparison of endogenous markers of glomerular filtration rate (GFR) (plasma symmetric dimethylarginine (SDMA) and estimated GFR (eGFR)) with a direct measure of GFR (using the plasma clearance of Inutest (In-GFR)), and a longitudinal evaluation of these markers in relation to the development of microalbuminuria, in young people with type 1 diabetes (T1D).
Methods: Longitudinal stored blood samples (n=1105) were available from 417 young people from the Oxford Regional Prospective Study (an inception cohort of 527 children followed for a median of 10.3(interquartile range 7.1-12.3)years), for measurement of SDMA and creatinine. Additional annually collected data on anthropometric parameters, HbA1c, insulin dose and 3 early morning albumin-creatinine ratios were available. In-GFR was measured in a representative sub-group of 183 subjects.
Main outcome measures: SDMA and eGFR.
Results: SDMA and eGFR were significantly and similarly associated with In-GFR (r=-0.38 and r=0.36 , p<0.001). Overall SDMA levels were lower in microalbuminuric (n=116) than normoalbuminuric subjects (n=301) (0.385±0.063 vs 0.412±0.059µmol/l, p<0.001), probably reflecting hyperfiltration. The pattern of change in SDMA levels with age differed between microalbuminuric and normoalbuminuric subjects. Whereas SDMA levels declined in both groups until the age of 16 years, thereafter they tended to rise only in microalbuminuric subjects, probably reflecting a decline in renal function.
Conclusions: In this longitudinal study of young people with T1D, measurement of SDMA, in contrast to eGFR, proved to be a reliable marker in identifying changes in filtration rates associated with the development of MA.