It has been demonstrated that low birth weights give rise to a reduction in nephron number and low glomerular size in the postnatal kidney. Oligonephropathy has been suggested to increase the risk for hypertension and renal insufficiency in adult life. The impact of markers of nephron mass on renal function and outcome in living kidney donors, however, hasn't been addressed so far.

To investigate the impact of birth weight, kidney volume, and kidney weight on the remaining kidney function and development of hypertension and proteinuria, we collected data from 106 living kidney donors, who underwent donor nephrectomy between 2003 and 2012. Samples were collected before nephrectomy, at +12, +36, and +60 months to assess eGFR and proteinuria. Birth weight was retrieved from donors' birth records. Kidney volume was measured from contrast-enhanced CT scans using the ellipsoid method. Kidney weight was calculated from the weight of the removed kidney and kidney volumes.

Renal function showed a positive correlation with birth weight at +12, +36, and +60 months after transplantation (R=0.357, p<0.001; R=0.299, p=0.017; R=0.371, p=0.037). The strongest link between birth weight and eGFR was observed in donors above the age of 50 years (R=0.631, p<0.001 at +12 months). No differences were observed between male and female donors at any time (p>0.05). Donors with pre-existing or new-onset hypertension showed significantly lower birth weight and a significant increase in serum uric acid levels after nephrectomy (p<0.05). Proteinuria at +12 months after transplantation showed a negative correlation with birth weight (R=-0.255, p=0.009). Kidney weight and kidney volume didn't show any impact on renal function after nephrectomy (p>0.05).

Low birth weight is a predisposing factor for outcomes of renal function, hypertension, and proteinuria after living kidney donation. Due to the natural decline of renal function with age, very little, if any, compensation by renal functional reserve remains in elderly donors, resulting in a strong correlation of remaining renal function and birth weight representing a marker of nephron mass. Greater renal functional reserve may contribute to better outcomes in younger donors in short-term follow-up. The impact of low birth weight on long-term outcome as risk of end-stage renal disease, cardiovascular disease, and overall mortality in living kidney donors needs to be addressed in upcoming studies.

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