Diagnostic imaging methods are commonly used to estimate kidney size. The most commonly used measurement for this purpose in clinical practice is the ratio of kidney length to the length of the L2 vertebral body on a ventrodorsal radiograph; this ratio should be between 2.5 and 3.5 in healthy adult dogs.1 The introduction of routine ultrasonographic examination of the abdomen in dogs has led to multiple methods for estimation of kidney size and volume with this modality, including a kidney length-to-L5 vertebral body ratio and the use of volumetric formulae based on maximum length of the kidney.2–4 It has been shown that although there is a positive correlation between kidney length or volume and body weight, the range of expected kidney size in healthy dogs is wide.5 The authors of a previous study6 attempted to correct for variations in kidney length attributable to body size by calculating KL:Aos from measurements in the sagittal plane for healthy adult dogs and proposed that values < 5.5 or > 9.1 indicate that kidneys are abnormally small or enlarged, respectively.6
Renal imaging studies of juvenile dogs are limited. Authors of one radiographic study7 found a greater kidney size in dogs < 1 year of age than in dogs > 1 year of age, whereas investigators of another study8 found no effect of age on renal size. A kidney length-to-L2 ratio is also more difficult to determine in young dogs owing to the radiographic appearance of the vertebral endplate.9 Ultrasonographic assessments of a litter of 5 Irish Setters from birth to 6 months of age revealed that kidney size relative to other body size variables was greater in puppies < 12 weeks of age than in adult dogs (between 3 and 7 years of age) of the same breed.9 After 12 weeks of age, relative kidney size was not significantly different from that for dogs > 1 year of age.9
Renal disease of any cause has an estimated incidence of 1.6% in the general canine population, and acute or chronic conditions can cause a change in overall kidney size.10 As the previous investigation of ultrasonographic kidney size in neonatal and juvenile dogs included a very small number of related animals, it is not appropriate to apply those results to a more general population of young dogs.9 The reproducibility of the KL:Ao has also not been established for dogs < 1 year of age, and it is difficult to determine whether kidney dimensions in young dogs with clinical signs of renal disease should be interpreted as normal or abnormal.
The purpose of the study reported here was to determine whether the previously characterized cutoffs for ultrasonographically determined KL:Ao are applicable to dogs 1 to 18 months of age. We also aimed to compare ultrasonographic kidney and aorta size measurements performed by observers of various experience levels when the same dogs were segregated into 3 age groups (approx 1, 6, and 12 to 18 months of age). We hypothesized that the KL:Aos for 1-month-old dogs would be significantly greater than those for the 2 older groups. We also hypothesized that intraobserver variability of KL:Aos would be low and that no significant interobserver variability would be found for any of the 3 age groups.
No third-party funding or support was received in connection with this study or the writing or publication of this manuscript. The authors declare that there were no conflicts of interest.
Presented in part as an oral presentation at the American College of Veterinary Radiologists Annual Scientific Conference, Phoenix, Ariz, October 2017.
The authors thank Bea VanKampen for technical assistance in acquiring ultrasonographic images.
Coefficient of variation
Kidney length-to-aorta diameter ratio
Kidney length-to-body weight ratio
Logiq e, GE Medical Systems, Milwaukee, Wis.
McKesson Radiology, version 12.1.1, McKesson Technology Solutions, Alpharetta, Ga.
SAS, version 9.4, SAS Institute Inc, Cary, NC.
SigmaPlot for Windows, version 11.0, Build 184.108.40.206, Systat Software Inc, San Jose, Calif.
2. Barella G, Lodi M, Sabbadin LA, et al. A new method for ultrasonographic measurement of kidney size in healthy dogs. J Ultrasound 2012;15:186–191.
3. Nyland TG, Kantrowitz BM, Fisher P, et al. Ultrasonic determination of kidney volume in the dog. Vet Radiol Ultrasound 1989;30:174–180.
4. Felkai CS, Vörös K, Vrabély T, et al. Ultrasonographic determination of renal volume in the dog. Vet Radiol Ultrasound 1992;33:292–296.
6. Mareschal A, d'Anjou MA, Moreau M, et al. Ultrasonographic measurement of kidney-to-aorta ratio as a method of estimating renal size in dogs. Vet Radiol Ultrasound 2007;48:434–438.
8. Lobacz MA, Sullivan M, Mellor D, et al. Effect of breed, age, weight and gender on radiographic renal size in the dog. Vet Radiol Ultrasound 2012;53:437–441.
10. Pelander L, Ljungvall I, Egenvall A, et al. Incidence of and mortality from kidney disease in over 600,000 insured Swedish dogs. Vet Rec 2015;176:656.
11. Salazar I, Yllera MM. Development of the mesonephros, metanephros and gonads in the foetal dog. Funct Dev Morphol 1991;1:59–63.
12. Rosenbaum DM, Korngold E, Teele RL. Sonographic assessment of renal length in normal children. AJR Am J Roentgenol 1984;142:467–469.
13. Han BK, Babcock DS. Sonographic measurements and appearance of normal kidneys in children. AJR Am J Roentgenol 1985;145:611–616.
14. Zerin JM, Meyer RD. Sonographic assessment of renal length in the first year of life: the problem of “spurious nephromegaly.” Pediatr Radiol 2000;30:52–57.
16. Sohn J, Yun S, Lee J, et al. Reestablishment of radiographic kidney size in Miniature Schnauzer dogs. J Vet Med Sci 2017;78:1805–1810.