Individual kidney depth determination is mandatory to assess split renal function in nephrography irrespective of age

Nephrography having been introduced more than 60 years ago still now is one of the most frequently used and informative procedures in Nuclear Medicine. Although being considered a well standardized method, a worldwide study in 34 centers in 21 countries revealed that determination of split kidney function shows unacceptable high variation, particularly in patients with a relative kidney function below 30%. Furthermore, kidney depth usually is not considered. The calculation of kidney depth by various formulas available, each claiming to be more predictive, is different in races and does not allow individual information, which particularly in patients with a diseased kidney may become unreliable. We investigated 331 patients (167m, 164f) aged 1 to 76 years (84 of them being less than 20 years old), where kidney depth has been estimated by means of sonography as well as by a lateral view gamma camera image obtained immediately after the investigation. At the age of 10 years the kidney depth may vary already by 20%, in some patients increasing to 30% at the age of 20 and showing further increase with increasing age. In adults, >50% show a depth difference between right and left kidney of >1cm. There is an excellent correlation between sonographic and nephrographic kidney depth determination, at mean there was no difference between the kidney depth of the right hand and left hand side. Furthermore, we demonstrate that the incorporation of waist circumference instead of body mass index into the formulas is more precise. These findings indicate that the assessment of split kidney function particularly in patients with kidney disease, transplant donors and atypical localization irrespective of age should be mandatory in clinical routine.