Open Journal of Nephrology, 2013, 3, 184-188 Published Online December 2013 (http://www.scirp.org/journal/ojneph) http://dx.doi.org/10.4236/ojneph.2013.34032 Open Access OJNeph Two-Hour Creatinine Clearance and Glomerular Filtration Rate Estimated from Serum Cystatin C and Creatinine in the Elderly to Preoperative Period Leopoldo Muniz da Silva, Pedro Thadeu Galvão Vianna, Mariana Takaku, Glênio Bittencourt Mizubuti, Yara Marcondes Machado Castiglia* Department of Anaesthesiology, Botucatu School of Medicine, São Paulo State University (UNESP), São Paulo, Brazil Email: *yarac@fmb.unesp.br Received July 22, 2013; revised August 18, 2013; accepted September 15, 2013 Copyright © 2013 Leopoldo Muniz da Silva et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT Introduction: The utility of estimates of glomerular filtration rate based on creatinine and cystatin C serum levels to assess renal function in older surgical patients remains to be determined. Objective: To determine whether 2h-creatinine clearance (CrCl-2h) can be an adequate substitute for glomerular filtration rate estimates obtained by measuring serum cystatin C and creatinine in the elderly at preoperation. Methods: A total of 102 consecutive elder patients undergoing pre-anesthesia evaluation for routine surgeries were included. Study subjects were allocated into three groups: Group 1 (G1)—hypertensive diabetic patients, Group 2 (G2)—hypertensive patients, and Group 3 (G3)—non-hypertensive and non-diabetic patients. Two-hour urine collection was performed and CrCl-2h adjusted for ultrasonic residual bladder volume was estimated. GFR was estimated based on creatinine and cystatin C serum levels. Bland-Altman analysis was used to compare methods. Results: The mean difference between the evaluated methods and CrCl-2h was <15 mL·min−1·1.73 m−2 for Cys-GFR, and >20 mL·min−1·1.73 m−2 for Cr-GFR in all groups. CrCl-2h adjusted for ultrasonic residual bladder volume did not differ from non-adjusted CrCl-2h in none of the groups. Con- clusion: Two-hour creatinine clearance was not an adequate substitute for GFR estimates based on creatinine and cys- tatin C serum levels in older patients at preoperation. The ultrasonic assessment of residual bladder volume had no sig- nificant influence on the calculation of two-hour creatinine clearance. Keywords: Renal Function; Creatinine Clearance; Cystatin C; Elderly 1. Introduction Subclinical renal disease, frequently seen in the diabetic and long-term hypertensive elderly, increases the risk associated with anesthesia and surgery, and enhances the susceptibility of these individuals to intraoperative renal failure, leading to high postoperative mortality rates [1-3]. The collection of urine output over 24 hours is one of the methods that have been used to assess renal function as it eliminates the potential error due to the existence of residual bladder volume, particularly in older people. However, a 24-h urine collection may not be feasible during preoperative evaluation delaying the availability of information for clinical evaluation [4]. In 1988, Cardenas et al. [5] described a small portable ultrasound device, specifically designed to determine bladder volumes that can be operated with minimal train- ing. According to these authors, volumes estimated using this noninvasive method correlate with those obtained by urethral catheterization. Thus, the assessment of renal function at 2-h intervals using ultrasound bladder scan to eliminate the bias associated with postmicturition resid- ual volume would be useful for the preoperative evalua- tion of elderly patients. Among intensive care patients, 2-h creatinine clearance has been demonstrated to be an adequate substitute for 24-h clearance, even in unstable patients [6]. Whether estimates of glomerular filtration rate based on creatinine and cystatin C serum levels are compared with 2-h creatinine clearance to assess renal function in older patients remains to be determined. Despite being an earlier marker of renal failure, cystatin C has not shown *Corresponding author. L. M. DA SILVA ET AL. 185 advantages over creatinine in the elderly [7]. Therefore, the purpose of this study was to assess whether creatinine clearance determined by a 2-hour urine collection ad- justed for residual bladder volume is an adequate substi- tute for glomerular filtration rate estimates obtained by measuring serum cystatin C and creatinine in older pa- tients before surgery. 2. Methods This study was approved by the Committee of Research Ethics of Botucatu Medical School, and written informed consent was obtained from all subjects. The study population consisted of 102 consecutive el- derly patients (≥65 years) who underwent pre-anesthe- sia evaluation for routine orthopedic, gastrointestinal, vascular, or gynecologic surgery in a tertiary university hospital. Study subjects were allocated into three groups: Group 1 (G1)—hypertensive diabetic patients, Group 2 (G2)— hypertensive patients, and Group 3 (G3)—non-hyperten- sive and non-diabetic patients. Patients were considered hypertensive and diabetic when diagnosis and specific treatment for these conditions had been established prior to admission. Patients with heart failure, renal failure re- quiring dialysis, anuria or kidney transplant were ex- cluded. All patients had surgical diseases and were re- ceiving preoperative in-patient care. For renal function assessment, post-void residual urine volume was checked using a BVI 5000 ultrasound scan- ner (Diagnostic Ultrasound Corporation, USA). With the patient lying supine, the scanhead was lubricated with conductive gel (gel pad Sontac 50) and positioned ap- proximately 5 cm above the symphysis pubis. Three scans were performed on each subject and the mean vo- lume from these scans was used as the mean urine vol- ume. Time count was then started. Patients were asked to complete urine collection in a special container for the next two hours. After one hour, a blood sample (15 mL) was obtained for the measurement of creatinine (mg/dL), urea (mg/dL), cystatin C (mg/L), and glycated hemoglo- bin (%). By the end of the two-hour interval, patients were asked to void in a container. From the total urine volume voided, a sample was collected for creatinine assessment (mg/dL). Ultrasonic residual volume was then measured again. Three readings were taken and the mean volume from these readings was added to the amount collected in the container. Adjusted urine volume was estimated by subtracting the initial residual volume from this sum. Urine output per minute (mL·min−1) was obtained by dividing the adjusted residual volume by the time elapsed to obtain it. Two-hour creatinine clearance (mL·min−1), or two-hour glomerular filtration rate (GFR), was estimated from the equation [urine creatinine (mg/dL) × adjusted two-hour urine volume (mL/min−1)/blood creatinine (mg/dL)]. Serum cystatin C measurements were performed by latex enhanced reagent (N Latex Cystatin C, Dade Behr- ing, Deerfield, IL, USA) using a Behring BN ProSpec analyser (Dade Behring) and Dade Behring calibrators. The test was performed according to the in- structions of the manufacturer. Serum creatinine was measured by a dry chemistry technique at the Chemistry Laboratory of the hospital. Creatinine-estimated GFR was calculated by the Cockcroft & Gault formula [8] where (GFRCG) = [140 − age (years) × weight (kg) / 72 × blood creatinine (mg/dL) × 0.85 (if female). GFR from cystatin C was calculated by the Larsson et al. formula [9] where (GFRLarsson) = [77.24 × cystatin C−1.2623 (mg/L)]. GFR and two-hour creatinine clearance were expressed per 1.73 m−2 of body surface area by multiplying measured values by 1.73 of body surface area. Anthropometric data, such as age (years), gender, weight (kg), height (m2) and body mass index (kg/m2) were collected during preoperative clinical evaluation. Statistical Analysis Sample size (n = 102) was calculated to detect a differ- ence of at least 15% between GFR by serum creatinine and two-hour creatinine clearance. Assuming a probabil- ity of 5% for a type I error and 20% for a type II error, 34 patients in each group would allow two-tailed compari- sons. Median and 25% - 75% percentiles were used as a measure of central tendency and variability due to non-normal distribution of the study data. Categorical variables were reported as absolute values and percent- ages. Comparisons were performed with the non-para- metric Kruskal Wallis test for continuous variables, fol- lowed by the a posteriori Dunn test for multiple com- parisons if P > 0.05. Significance was set at P < 0.05. CrCl-2h adjusted for ultrasonic residual bladder volume and not adjusted CrCl-2h was compared by Mann-Whit- ney test. Because analysis with correlation and least squares li- near regression is fundamentally misleading, Bland and Altman analysis [10] was used to compare the differ- ences between the methods for glomerular filtration rate measurement (Y axis) plotted against their mean (X axis). Bias was defined as the mean value of the differences between methods. If the 95% limits of agreement (mean ± 2SD) between methods were not clinically important, methods were considered interchangeable. The confi- dence intervals for the 95% limits of agreement were calculated by mean difference ±1.96 standard deviation of the differences. Bland and Altman analysis [10] of the GFR estimates was performed with Medcalc (Medical Open Access OJNeph L. M. DA SILVA ET AL. Open Access OJNeph 186 Cr-GFR - CrCl-2h were showed in Table 1. Software, Mariakerke, Belgium). CrCl-2h adjusted for ultrasonic residual bladder vol- ume did not differ from non-adjusted CrCl-2h in all pa- tients (Figure 2). 3. Results Patient median age was 71 years (65 - 88 years). Males accounted for 66.34% of the study population. In diabetic patients, median glycated hemoglobin was 7.2%. 4. Discussion The assessment of renal function using creatinine con- centration as a marker has several limitations in the eld- erly. Two hour-creatinine clearance would then be an im- portant alternative for assessing renal function serially and at short intervals. Study groups were homogeneous according to age, gender and body mass index (kg·m−2). There was no sta- tistically significant difference in adjusted urine volume, two-hour creatinine clearance (CrCl-2h), creatinine-esti- mated glomerular filtration rate (Cr-GFR) and Cystatin-C estimated GFR (Cys-GFR). In this study, CrCl-2h was compared with glomerular filtration rate and estimates from creatinine and cystatin C. Our data showed that CrCl-2h better agreed with cys- tatin C-estimated GFR (Larsson equation) than with creatinine-estimated GFR (Cockcroft & Gault equation) in older patients. The mean difference between the evalu- ated methods and CrCl-2h was < 15 mL·min−1·1.73 m−2 for Cys-GFR, and >20 mL·min−1·1.73 m−2 for Cr-GFR in all groups. A mean difference between methods of 18 - The mean differences between the evaluated methods and CrCl-2h were 3.67 mL·min−1·1.73 m−2 for Cys-GFR, and 27.44 mL·min−1·1.73 m−2 for Cr-GFR in G1; 2.29 mL · min − 1 · 1 .73 m − 2 f o r Cys -GFR and 22 .9 6 mL·min−1 ·1.73 m−2 for Cr-GFR in G2; 13.10 mL · min − 1 · 1 .73 m − 2 f o r Cys -GFR and 40 .4 0 mL·min−1·1.73 m−2 for CR-GFR in G3 (Figure 1). Limits of agreement between Cys-GFR - CrCl-2h and Figure 1. Bland-Altman plot for differences between Cys-GFR, Cr-GFR and two-hour creatinine clearance (CrCl-2h) per group (G1-G3) in the preoperative period. Horizontal lines indicate the mean reflecting the mean difference and the span between +1.96 SD and −1.96 SD of the mean difference between CrCl-2h and the methods evaluated (Cys-GFR and Cr-GFR). L. M. DA SILVA ET AL. 187 Table 1. Bland-Altman for differences between Cys-GFR, Cr-GFR and two-hour creatinine clearance (CrCl-2h) per group (G1-G3) in the preoperative period. Limits of agreement - Upper limit (+1.96 SD) (CI 95%) and lower limit (−1.96 SD) (CI 95%) (mL·min−1·1.73 m−2). Limits of agreement Groups Cystatin C-GFR* G1 G2 G3 Upper limit (CI 95%) 187.50 (131.02; 144.03) 149.58 (99.74; 190.26) 218.60 (155.46; 281.75) Lower Limit (CI 95%) −180.26 (−236.77; −126.76) −145.00 (−194.55; −104.33) −192.40 (−255.54; −129.26) Creatinine-GFR* Upper limit (CI 95%) 220.73 (161.35; 280.14) 171.62 (125.96; 217.33) 250.51 (183.65; 315.89) Lower Limit (CI 95%) −165.85 (−225.25; −106.46) −125.80 (−171.4; −80.03) −169.71 (−239.70 ; −107.47) *mL·min−1·1.73 m−2. Figure 2. Comparison of CrCl-2h adjusted (B) and not ad- justed (A) for ultrasonic residual bladder volume (mL·min−1·1.73 m−2) in elder patients during the preopera- tive period. Box plots - Bars represent median values, boxes represent interquartile ranges, and whishers show 95% confidence intervals. Mann-Whitney Test: A = B in G1, G3 and G3. 20 mL·min−1·1.73 m−2 [6] was considered acceptable. However, although CrCl-2h values showed a better agreement with Cys-GFR, the wide limits of agreement between these methods, which reflect the great variation of the results obtained, did not allow concluding that these methods actually agree and can be used inter- changeably. In intensive care patients, Gutierrez et al. [6] found a close correlation between 24-h and 2-h creatinine clear- ance that remained even with the use of diuretics or in the presence of low or irregular diuresis, suggesting that such methods are interchangeable. These authors further report that 24-h creatinine clearance correlated poorly with GFR estimated by the Cockcroft & Gault equation. Diabetes and hypertension, which have the kidney as a target organ, tend to worsen renal function in older pa- tients. The diabetic and hypertensive elderly included in this study was receiving preoperative care for routine surgery, and was, therefore, well compensated. Moreover, those who were diabetic had satisfactory previous gly- cemia control as measured by glycated hemoglobin. This fact may explain why no difference in preoperative renal function was detected among groups. Studies comparing cystatin C with creatinine meas- urements have produced conflicting results. While some have demonstrated that cystatin C is more sensitive than creatinine in detecting renal failure [11-13], others have reported no difference between these markers [7,14]. This disparity is likely to be due to differences in study population. In patients with normal or slightly reduced renal function, cystatin C seems to be superior to creati- nine. In contrast, in patients with a marked decline in renal function, differences between cystatin C and creati- nine are smaller as frequently observed in older patients [11,14]. Because the formula of Cockcroft & Gault may over- estimate renal function when GFR >60 mL·min−1·1.73 m−2, cystatin C is clearly more useful in these cases. In this study, in which individuals with markedly reduced renal function were not included and most elderly pa- tients showed GFR >60 mL·min−1·1.73 m−2, cystatin C was a more adequate marker of renal function than CrCl-2h [15]. The Cockcroft & Gault formula might have overestimated GFR, and this would explain the in- creased difference between mean CrCl-2h and mean Cockcroft & Gault formula values seen in our older pa- tients. However, other studies have demonstrated that cystatin C has no advantages over creatinine in popula- tion with GFR < 60 mL·min−1·1.73 m−2 [14]. Thus, the severity of pre-existing renal disease should be consid- ered when selecting the method to be used for the as- sessment of renal function in older patients. The use of ultrasound to measure residual bladder vo- lume in order to obtain more precise two-hour urine vo- lume estimates is essential in the elderly. In this popula- tion, physiological disorders such as prostatic hypoplasia and bladder prolapse can lead to underestimation of the two-hour volume measured. Nonetheless, whether ad- justed or not for residual bladder volume, CrCl-2h values did not differ among our patients. An explanation for this Open Access OJNeph L. M. DA SILVA ET AL. 188 finding is that few residual amounts cannot be easily de- tected by ultrasound examination and this might have influenced the interpretation of the results. Diurnal variation in diuresis is another factor that has been suggested to interfere with CrCl-2h assessment. However, creatinine clearance estimates obtained at a shorter interval (8 hours) have been demonstrated to be as accurate as 24-h clearances [16]. In conclusion, two-hour creatinine clearance was not an adequate substitute for GFR estimates based on crea- tinine and cystatin C serum levels in older patients at preoperative period. The ultrasonic assessment of resid- ual bladder volume had no significant influence on the calculation of two-hour creatinine clearance. REFERENCES [1] S. Klag, P. K. Whelton, B. L. Randall, et al., “Blood Pressure and End-Stage Renal Disease in Men,” The New England Journal of Medicine, Vol. 334, No. 1, 1996, pp. 13-18. [2] M. C. B. S. Benarab, Y. M. M. Castiglia, P. T. G. Vianna, et al., “Two-Hours Evaluation of Renal Function in the Elderly,” Revista Brasileira de Anestesiologia, Vol. 55, No. 3, 2005, pp. 269-278. http://dx.doi.org/10.1590/S0034-70942005000300003 [3] Y,Yi-sun, C. H. Peng, C. K. Lin, et al., “Use of Serum Cystatin C to Detect Early Decline of Glomerular Filtra- tion Rate in Tape 2 Diabetes,” Intern med., Vol. , No. , 2007, pp. 801-806. [4] J. R. Friedman, D. C. Norman and T. T. Yoshikawa, “Correlation of Estimated Renal Function Parameters Versus 24-Hour Creatinine Clearance in Ambulatory El- derly,” Journal of the American Geriatrics Society, Vol. 37, No. 2, 1989, pp. 145-149. [5] D. D. Cardenas, E. Kelly, J. N. Krieger, et al., “Residual Urine Volumes in Patients with Spinal Cord Injury: Measurement with a Portable Ultrasound Instrument,” Archives of Physical Medicine and Rehabilitation, Vol. 69, No. 7, 1988, pp. 514-516. [6] M. Gutierrez, G. S. Perez, E. Banderas-Bravo, et al., “Replacement of 24h Creatinine Clearance by 2-h Creati- nine in Intensive Care Unit Patients: A Single-Center Study,” Intensive Care Medicine, Vol. 33, No. 11, 2007, pp. 1900-1906. http://dx.doi.org/10.1007/s00134-007-0745-5 [7] N. J. Van Den Noortgate, W. H. Janssens, J. R. Delanghe, et al., “Serum Cystatin C Concentration Compared with Other Markers of Glomerular Filtration Rate in the Old Old,” Journal of the American Geriatrics Society, Vol. 50, No. 7, 2002, pp.1278-1282. http://dx.doi.org/10.1046/j.1532-5415.2002.50317.x [8] D. W. Cockcroft and M. H. Gault, “Prediction of Creati- nine Clearance from Serum Creatinine,” Nephron, Vol. 16, No. 1, 1976, pp. 31-41. http://dx.doi.org/10.1159/000180580 [9] A. Larsson, J. Malm, A. Grubb, et al., “Calculation of Glomerular Filtration Rate Expressed in mL/min from Plasma Cystatin C Values in mg/L,” Scandinavian Jour- nal of Clinical and Laboratory Investigation, Vol. 64, No. 1, 2004, pp. 25-30. [10] J. M. Bland and D. G. Altman, “Statistical Methods for Assessing Agreement between Two Methods of Clinical Measurement,” The Lancet, Vol. 327, No. 8476, 1986, pp. 307-310. http://dx.doi.org/10.1016/S0140-6736(86)90837-8 [11] D. J. Newman, H. Thakkar, R. G. Edwards, et al., “Serum Cystatin C Measured by Automated Immunoassay: A More Sensitive Marker of Changes in GFR than Serum Creatinine,” Kidney International, Vol. 47, No. , 1995, pp. 312-318. http://dx.doi.org/10.1038/ki.1995.40 [12] B. Stabuc, L. Vrhovec, M. Stabuc-Silih, et al., “Improved Prediction of Decreased Creatinine Clearance by Serum Cystatin C: Use in Cancer Patients before and during Chemotherap,” Clinical Chemistry, Vol. 1, No. , 2000, pp. 29-34. [13] D. Fliser and E. Ritz, “Serum Cystatin C Concentration as a Marker of Renal Dysfunction in the Elderly,” American Journal of Kidney Diseases, Vol. 37, No. 1, 2001, pp. 79-83. [14] E. Coll, A. Botey, L. Alvarez, et al., “Serum Cystatin C as a New Marker for Noninvasive Estimation of Glmeru- lar Filtration Rate and as a Marker for Early Renal Im- pairment,” American Journal of Kidney Diseases, Vol. 36, No. 1, 2000, pp. 29-34. http://dx.doi.org/10.1053/ajkd.2000.8237 [15] T. H. Goldberg and M. S. Fin kelstein, “Difficulties in Estimating Glomerular Filtration Rate in the Elderly,” Archives of Internal Medicine, Vol. 147, No. 8, 1987, pp. 1430-1433. http://dx.doi.org/10.1001/archinte.1987.00370080066014 [16] S. L. Markantonis and E. Kioupaki-Agathokleusous, “Can Two, Four or Eight-Hour Urine Collections after Voluntary Voiding Be Used Instead of Twenty-Four Col- lections for the Estimation of Creatinine Clearance in Healthy Subjects?” Pharmacy World and Science, Vol. 20, No. 6, 1998, pp. 258-263. Open Access OJNeph http://dx.doi.org/10.1590/S0034-70942005000300003 http://dx.doi.org/10.1007/s00134-007-0745-5 http://dx.doi.org/10.1046/j.1532-5415.2002.50317.x http://dx.doi.org/10.1159/000180580 http://dx.doi.org/10.1016/S0140-6736(86)90837-8 http://dx.doi.org/10.1038/ki.1995.40 http://dx.doi.org/10.1053/ajkd.2000.8237 http://dx.doi.org/10.1001/archinte.1987.00370080066014