The effect of fluid intake on renal length measurement in adults

The Effect of Fluid Intake on Renal LengthMeasurement in Adults Fatih Kantarci, MD,1 Ismail Mihmanli, MD,1 Ibrahim Adaletli, MD,1 Harun Ozer, MD,1Fatih Gulsen, MD,1 Alev Kadioglu, MD,2 Ayca Altug, MD,1 Omer Uysal, MSc3 1 Department of Radiology, Istanbul University, Cerrahpasa Medical Faculty, 34300 Istanbul, Turkey2 ALKA Medical Imaging Center, Istanbul, Turkey3 Department of Biostatistics, Istanbul University, Cerrahpasa Medical Faculty, 34300 Istanbul, Turkey Received 24 May 2005; accepted 3 November 2005 ABSTRACT: Purpose. To evaluate whether oral fluidintake has an effect on renal length as determined Unilateral or bilateral reduction or increase in kidney size is an important sign of many re- nal diseases. Thus, knowledge of normal sono- Methods. We studied 524 adult patients who were re- graphic size is important when evaluating patients ferred to our ultrasound unit with complaints other than with renal diseases. Estimation of renal size via urinary tract symptoms. The mean age of the patientswas 44 years (range 17–76). All of the measurements sonography can be performed by measuring renal were performed with the patient in the prone position.
length, renal volume, or cortical volume or thick- The renal length of each kidney was measured by the ness.1–5 Renal length and cortical thickness are same observer before and after oral fluid intake. Stu- routine measurements in the diagnosis and dent’s t-test was applied for the statistical significance follow-up of most disease conditions involving the of renal length measurements before and after hydra- tion. Analysis of variance was performed for the effect In most institutions, sonographic evaluation of of age and sex on the renal length measurements.
the genitourinary tract includes examination of Results. The mean renal length on the right side the kidneys, ureter (if possible), and urinary blad- was 106.2 6 5.5 mm and 107.5 6 5.7 mm on the left der. Therefore, measurements regarding the kid- side before hydration. There was no statistically sig- neys, such as renal length, can be performed in a nificant difference between right and left side renallength measurements. After hydration, the mean re- hydrated or nonhydrated state. Adequate hydra- nal length was 113.5 6 6.1 mm on the right side and tion may be provided intravenously or via oral fluid 114.6 6 6.6 mm on the left side. The mean increase in intake,10,11 and is used primarily for accurate sono- renal length after hydration was statistically signifi- graphic evaluation of the bladder. The diagnosis of cant (P < 0.001) and was 6.8% on the right side and various disease conditions of the urinary tract— 6.6% on the left side. Sex and age did not affect the such as obstruction or differentiation between a parapelvic cyst and hydronephrosis—requires ad- Conclusions. Oral fluid intake causes a statistically equate hydration.10–12 The effects of hydration on significant increase in renal length. This observation the renal pelvis have been widely studied10,12–14; should be taken into consideration when renal length however, the effect on renal length by means of so- measurements are clinicallly important. V Periodicals, Inc. J Clin Ultrasound 34:128–133, 2006; nography has not been established. The aim of our Published online in Wiley InterScience (www.inter- study was to evaluate whether oral fluid intake DOI: 10.1002/jcu.20225 has an effect on renal length measurement.
Keywords: ultrasonography; kidneys; hydration; renallength; measurement From October 2003 to September 2005, we pro-spectively measured kidney size in adult patients who were attending our ultrasound unit for rea- sons other than renal examinations. The inclu- JOURNAL OF CLINICAL ULTRASOUND—DOI 10.1002/jcu sion criterion for the study was normal appear- amination), the patients were asked to empty their ance of the kidneys on sonographic examination.
bladder just before the sonographic examination.
Exclusion criteria were chronic renal failure, hyper- For the second part, the patients were subdivided tension, diabetes mellitus, chronic heart failure, into 2 groups. Group 1 patients (n ¼ 50) consumed history of hemodialysis or peritoneal dialysis, uni- 1.5 l of water within 1 hour, while group 2 patients lateral or partial nephrectomy, renal transplanta- (n ¼ 50) remained dehydrated. The second exami- tion, any congenital anomaly in 1 or both of the nation for group 1 patients (hydrated group) was kidneys, presence of a unilateral kidney, hydro- performed when the patient noted bladder filling nephrosis, renal cysts and/or neoplasms, renal cal- but no urgency. The second examination for group culi, and abnormal parenchymal echo appearance 2 patients (dehydrated group) was performed ap- on initial examination. Written informed consent proximately 1.5 to 3 hours after the baseline exam- was obtained from all patients. The study was per- ination. The timing was determined by an assist- formed according to the guidelines of the Helsinki ant who was blinded to the renal length measure- ments but not the hydration status. The physician The study included 524 patients (group A, 291 who performed the examination was blinded to male, 233 female) in which the examiner was not both the hydration status of the patients and the blinded to the hydration status or the renal renal length measurements. Measurements were length measurements. The mean age of the patients noted by an assistant who was also blinded to the was 44 6 12.3 years (range 17–76). An additional 100 patients (group B, 52 male, 48 female) were SPSS software for Windows (version 7.5; SPSS studied in which the examiner was both blinded to Inc., Chicago, IL) was used for statistical analy- the hydration status and the renal length mea- sis. The patients in group A were subgrouped surements. The mean age of these patients was based on side (right and left), gender (male and female), or age differences. Grouping based on The examination was performed in a quite, age was made according to decades. Patients in temperature-controlled room (228C) between 9 subgroup 1 were less than 30 years old, subgroup and 12 A.M. Real-time gray-scale sonography was 2 between 30 and 39 years, subgroup 3 between performed with a 2–5-MHz convex transducer 40 and 49 years, subgroup 4 between 50 and connected to a Sonoline Elegra scanner (Siemens 59 years, subgroup 5 between 60 and 69 years, Medical Solutions, Issaquah, WA). All the exami- and subgroup 6 older than 69 years. Statistical nations were performed by a single experienced analysis included the overall comparison of the radiologist. Renal length measurements were renal length measurements on each side (right and performed for each kidney while patients were in left) before and after hydration via paired-sample the prone position. All measurements were per- t-test. The comparison between gender groups and formed in deep inspiration. Both renal poles were age groups was performed via independent-sample identified and the measurements were performed.
t-test. The changes among gender groups, side-to- At least 3 consecutive measurements were taken side differences, and age groups between pre- in the prone position for each kidney, and the hydration and posthydration measurements were mean of these measurements was calculated foreach kidney.
Patients in group A were all hydrated, and the examinations were performed before and afterhydration. All patients fasted the night beforethe examination and oral fluid intake was re-stricted for a minimum of 6 hours before the ex-amination. For the first part of the study (base-line examination), the patients were asked toempty their bladder just before the sonographicexamination. For the second part, the patientsingested 1.5 l of water within 1 hour. The secondpart of the examination was performed when thepatients noted bladder filling but no urgency.
All patients in group B fasted the night before the examination, and oral fluid intake was re-stricted for a minimum of 6 hours before the exam-ination. For the first part of the study (baseline ex- FIGURE 1. Change in renal length (mm) before and after hydration.
VOL. 34, NO. 3, MARCH/APRIL 2006—DOI 10.1002/jcu FIGURE 2. Difference in millimeters between the prehydration and posthydration renal length measurements.
Mean Renal Length Measurements among Male and Female Subjects Before and After Hydration and the Percent studied via analysis of variance. The patients in were statistically significant (P < 0.001) (Fig- group B were assessed via paired-sample t-test for ures 1, 2). The renal length measurements were comparison of the baseline renal length measure- not statistically significant before or after hydra- ments on each side (right and left) with the second tion among males and females or among different measurements for group 1 and group 2 patients.
age groups (Tables 1, 2). Analysis of variance The amount of change (percent) was calculated for revealed no significant effect of age, side, or gen- both group 1 and group 2. A P value of less than der on renal length measurements (P > 0.05).
0.05 was considered statistically significant.
In group B, the mean renal length at baseline examination was 101.7 6 7.5 mm (right side,range 90.5–118.9 mm) and 102.3 6 6.9 mm (left side, range 91.2–119.7 mm) for the patients who In group A, the mean renal length before hydra- were hydrated (group 1), and 102.6 6 9.5 mm (right tion was 106.3 6 5.6 mm on the right side and side, range 90.4–119.2 mm) and 103.1 6 9.8 mm 107.5 6 5.8 mm on the left side. Before hydration, (left side, range 90.1–121.1 mm) for patients who there were no statistically significant differences remained dehydrated (group 2). The mean renal between the right and left side renal length length after hydration was 107.4 6 8.1 mm (right measurements (P > 0.05). After hydration, the side, range 91.1–123.4 mm) and 108.2 6 7.2 mm mean renal lengths were 113.5 6 6.1 mm and (left side, range 95.1–122.8 mm) for patients in 114.6 6 6.6 mm on the right and left sides, group 1. The second examination for group 2 re- respectively. The mean increase in renal length vealed a mean renal length of 102.8 6 9.7 mm was 6.8% and 6.6% on the right and left sides, (right side, range 90.6–120.6 mm) and 103.2 6 respectively. After hydration, the comparison 9.7 mm (left side, range 90–120.7 mm). The sta- between the right and left renal length measure- tistical analysis revealed a significant change in ments was not statistically significant (P > 0.05).
group 1 (P < 0.001), while there was no statisti- The renal length measurements before and after cally significant change in group 2 (P ¼ 0.164 for hydration on the right and left sides separately right side, P ¼ 0.251 for left side). The mean re- JOURNAL OF CLINICAL ULTRASOUND—DOI 10.1002/jcu Mean Renal Length Measurements among Different Age Groups Before and After Hydration and the Percent Increase nal length increased 5.6% (right side) and 5.8% glomerular filtration rate (GFR) and increases the (left side) in group 1. The change was 0.1% (right natriuresis.17 Increase in natriuresis after oral and left sides) increase for group 2.
fluid intake may manifest as mild or moderatehydronephrosis, a common observation duringroutine sonographic examination of the kidneys.17We cannot directly examine the histopathological changes in the kidneys after fluid intake, and we Sonographic evaluation of the kidney is generally do not know what changes occur in the glomerulus a part of the urinary tract examination, in which and collecting tubules in this situation. On the the kidneys, ureter, and bladder are evaluated.15 other hand, the gross morphological changes may The kidneys may be well identified in a nonfast- be studied with imaging modalities such as sono- ing patient; however, fasting may be desired to graphy, CT, or MRI.1–5,18 We hypothesized that limit bowel gas.15 When the kidneys are part of the increased amount of urine production caused a full urinary tract examination (ie, kidneys, by oral fluid intake probably distended the col- ureter, and bladder), high fluid intake is com- lecting ducts, and this in turn may manifest as monly used to accelerate urine production.10 The an increase in the dimension of the kidneys.
examination is performed by filling the bladder The position of the patient is probably one of with a moderate amount of urine. Therefore, it is the most important aspects of sonographic exami- essential to know the effects of fluid intake on re- nation of the kidneys. The kidneys are ovoid on nal physiology and the morphological changes cross-section, with the largest dimension proceed- associated with it. The hydration status of the ing anteromedially to posteromedially. Therefore, patients by way of oral fluid intake varies from longitudinal views of the kidney will demonstrate patient to patient. Assessing the hydration status a different shape depending on how the view was is a complex issue and can be accomplished by obtained.19,20 For this reason, we examined patients measuring body weight, hemoglobin and hemato- in the prone position. A posterior approach allows crit levels, serum osmolality, sodium concentra- the transducer to be closer to the kidneys, and the tion, and urine-specific gravity and osmolality and measurement technique is more standardized.
via bioelectrical impedence analysis.16 In our study, There is little information available regarding although the patients consumed 1.5 l of water, a the accuracy of sonography in the evaluation of re- standardized hydration status was not achieved nal size.21 Renal volume measurements calculated and should be noted as a limitation of the study.
with the ellipsoid formula applied to sonographic Therefore, we attributed changes in renal length images can result in a considerable systematic un- on sonographic examination to changes in fluid derestimation of renal volume and have large intra- intake and excretion on the part of the patient.
observer and interobserver variations.1,5 On the Although the renal effects of hydration are not other hand, it has been suggested that renal length well defined, it is said that hydration lowers the measurements are more reliable than volume VOL. 34, NO. 3, MARCH/APRIL 2006—DOI 10.1002/jcu measurements. Ablett et al22 studied interobserver In conclusion, it is essential to understand that and intraobserver variations in renal length mea- renal length measurements may change after surements and found that the magnitude of varia- oral fluid intake. This fact should be kept in mind tion is similar whether the left or right kidney is for disease processes in which renal length meas- measured and whether measurements are made urements are clinically important and are used by 1 or multiple sonographers. They reported that the SDs ranged between 4.8 and 7.2 mm. Ema-mian et al1 found a relative SD of 4%–5% for renallength in adults. In our study, in which the exam- iner was blinded to both the hydration status and 1. Emamian SA, Nielsen MB, Pedersen JF. Intra- renal length measurements, no statistically signif- observer and interobserver variations in sono- icant change in renal length measurements were graphic measurements of kidney size in adult vol- found in patients who were not hydrated. On the unteers. A comparsion of linear measurements and other hand, an approximately 6% increase was volumetric estimates. Acta Radiol 1995;36:399.
seen in patients who were hydrated in the blinded 2. Brandt TD, Neiman HL, Dragowski MJ, et al.
study group. In the nonblinded group in which all Ultrasound assessment of normal renal dimen- the patients were hydrated, the change was ap- proximately 7%. However, in the studies by Ablett 3. Spiegl G, Jeanty P, Kittel F, et al. Ultrasonic mea- et al22 and Emamian et al,1 the hydration status sure of the normal kidney. J Belge Radiol 1982; of the patients was not standardized. The great 4. Emamian SA, Nielsen MB, Pedersen JF, et al.
interobserver and intraobserver difference may Kidney dimensions at sonography: corrrelation be due to the hydration status of the patients.
with age, sex, and habitus in 665 adult volunteers.
For practical reasons, it was not possible at the beginning of our study to create a blinded study 5. Bakker J, Olree M, Kaatee R, et al. Renal volume design. Therefore, we conducted a satellite- measurements: accuracy and repeatability of US blinded study design in a new but smaller group compared with that of MR imaging. Radiology of patients due to the significant bias introduced by a nonblinded study. Our results in the blinded 6. Banholzer P, Haslbeck M, Edelmann E, et al. Sono- study group confirmed the change in renal graphic changes in the size of the kidneys in type I length measurements (6% for the blinded group, diabetes as a method of early detection of diabeticnephropathy. Ultraschall Med 1988;9:255.
7% for the nonblinded group), which was pro- 7. Sustic A, Mavric Z, Fuckar Z, et al. Kidney length bably caused by the hydration of the patients.
in postoperative acute renal failure. J Clin Ultra- A reduction in renal length is considered an in- dicator of chronic renal disease, with a value of 8. McRae CU, Shannon FT, Utley WLF. Effect on re- 9 cm or less indicating irreversible disease.23 It nal growth of reimplantation of refluxing ureters.
may also be used in follow-up for the progression of a disease process affecting the kidneys; there- 9. Troell S, Berg U, Johansson B, et al. Ultrasono- fore, accurate renal length measurements are graphic renal parenchymal volume related to kid- important.6–9 In our study, we found an approxi- ney function and renal parenchymal area in chil- mately 7% increase in renal length measurements dren with recurrent urinary tract infections andasymptomatic bacteriuria. Acta Radiol 1984;25:411.
after oral fluid intake. Based on our results, one 10. Morin ME, Baker DA. The influence of hydration may estimate that renal length measurements are and bladder distension on the sonographic diagnosis prone to variability depending on the fluid intake of hydronephrosis. J Clin Ultrasound 1979;7:192.
of the patient. An important aspect of renal sono- 11. Shokeir AA, Provoost AP, el-Azab M, et al. Renal graphic examination is sequential imaging change Doppler ultrasound in children with normal upper in which the enlargement or reduction of the kidney urinary tracts: effect of fasting, hydration with is associated with a disease pattern. We believe normal saline, and furosemide administration.
that in such a situation, the patients are their own control with the awareness that the same 12. Nicolau C, Vilana R, Del Amo M, et al. Accuracy of level of fluid intake should be present when se- sonography with a hydration test in differentiatingbetween excretory renal obstruction and renal quential sonograms are obtained. Our study in- sinus cysts. J Clin Ultrasound 2002;30:532.
cluded patients without renal complaints and 13. Hasch E. Changes in renal pelvic size in children sonographically normal kidneys; however, the after fluid intake demonstrated by ultrasound.
effect of hydration on renal length in abnormal or diseased kidneys is not known. This issue should 14. Meola M, Giuliano G, Morelli E, et al. Ultrasound diagnosis of suspected urinary tract obstruction JOURNAL OF CLINICAL ULTRASOUND—DOI 10.1002/jcu using a stimulated diuresis test. Nephron 1995; 19. Middleton WD, Kurtz AB, Hertzberg BS. Kidney.
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21. Hricak H, Lieto RP. Sonographic determination of 17. Anastasio P, Cirillo M, Spitali L, et al. Level of renal volume. Radiology 1983;148:311.
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22. Ablett MJ, Coulthard A, Lee RE, et al. How reli- able are ultrasound measurements of renal length 18. Tublin ME, Tessler FN, McCauley TR, et al. Effect in adults? Br J Radiol 1995;68:1087.
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