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Ali Duzova, Fatos Yalçınkaya, Esra Baskin, Aysin Bakkaloglu, Oguz Soylemezoglu, Prevalence of hypertension and decreased glomerular filtration rate in obese children: results of a population-based field study, Nephrology Dialysis Transplantation, Volume 28, Issue suppl_4, November 2013, Pages iv166–iv171, https://doi.org/10.1093/ndt/gft317
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Abstract
Obesity has risen considerably in the Western world and the trend is increasing in non-Western, developing countries, as well. Several school screening studies showed the relation between body mass index and hypertension. In adults, obesity is associated with an increased risk of development and progression of kidney disease. However, data at the epidemiological level are limited, both for children and adults. The aim of this study was to determine the prevalence of obesity and evaluate its association with hypertension and glomerular filtration rate (GFR) among children in Turkey.
A population-based field study in which individuals were accessed by house visits throughout Turkey has been conducted. The study sample (3622 children; 5–18 years; 49.6% female, mean age 11.88 ± 3.40 years) was selected to represent the Turkish population regarding geographical region, gender and age (5–18 years). Obesity was defined as the body mass index ≥95th percentile for age and gender. The Schwartz formula was used to estimate GFR. Blood pressure (BP) percentile was determined according to age, gender and length.
The prevalence of overweight, obesity and hypertension were 9.3, 8.9 and 6.1%, respectively. Logistic regression analysis revealed urban area (OR 1.50; 95% CI 1.15–1.96; P = 0.003) as an independent risk for obesity and age decreased (OR 0.921; 95% CI 0.890–0.924; P < 0.001) risk for obesity. Obese children had the highest rate of hypertension (11.4 versus 5.6%; P < 0.001; OR 2.17, 95% CI 1.49–3.17; P < 0.001) and stage II hypertension (3.8 versus 0.7%; OR 6.01, 95% CI 2.93–12.33; P < 0.001). Systolic and diastolic BP z-scores were significantly higher in obese children. The mean estimated (eGFR) was lower in obese children (122.7 ± 21.6 versus 129.4 ± 23.1, P < 0.001). The rates of children with eGFR < 90 and <75 mL/min/1.73 m2 were higher in obese patients, but did not reach statistical significance.
Our nation-wide population-based field study among children showed that the prevalence of obesity is increasing in Turkey. The prevalence of hypertension and stage II hypertension, BP z-scores and eGFR were associated with obesity. We suggest that obese children are future candidates for chronic kidney disease. Longitudinal research is necessary to better understand these associations. Strategies for the prevention and management of obesity are also important for emerging countries and for children.
Comments
Dear sir We read the response of Duzova et al. in response to comments raised by Prof. Tomoyuki Kawada with great interest (1). Although we agree with Duzova et al. on account of their justification of not using new equation (2) but we are disappointed with the statement by Duzova et al. in their response that their study aim was not to predict obesity. This statement is contradictory to what they have mentioned in their orignal article " this study aims to determine prevalence of obesity" (1). As reader, we find this statement very confusing and misleading. On what account one can determine prevalence of obesity if authors did not predict obesity in first place. References 1. Duzova A, Yalcinkaya F, Baskin E et al. Prevalence of hypertension and decreased glomerular filtration rate in obese children: results of a population-based field study. Nephrol Dial Transplant 2013;28 Suppl 4:iv166-171. Reference 2. Schwartz GJ, Munoz A, Schneider MF et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol 2009;20:629-637.
Conflict of Interest:
None declared
Dear Sirs,
We appreciate the comments by Professor Tomoyuki Kawada about the method we used to estimate eGFR. Professor Takeda reported that when he conducted "a simple simulation study the formula with k 0.7 presented a higher eGFR than with the age-adjusted formula, in subjects under the age of 20 with a serum creatinine <1.1 mg/dL and height >160cm"; and recommended "to conduct a logistic regression analysis by using age- adjusted eGFR for predicting obesity".
To start with, in our study our aim was not to predict obesity but evaluate the association between obesity and eGFR [1]. We had used original Schwartz formula [k x length (cm)/creatinine (mg/dL)]: k was 0.70 if male >13 years and 0.55 otherwise, as suggested by Schwartz and Gauthier in 1985 [2], following the first formula suggested in 1976 [3]. In their article (1985) Schwartz and Gauthier suggested that "GFR could be better estimated for boys of any age by the linear bivariate equation [1.5 x (age) + 0.5 x (height/creatinine); r: 0.82; p <0.001) and that this equation yielded slightly better results than did 0.7 x (height/creatinine) [2]. However, in general practice what most clinicians use is the formula we used in our study; not original formula for girls [k 0.55] and age adjusted formula for boys.
We, however, repeated our analysis using age adjusted formula in boys and original formula in girls (k: 0.55). The association between BMI groups and eGFR did not differ: children with obesity had lower mean eGFR [underweight 129.81 +/- 20.20; normal BMI 125.40 +/- 18.17; overweight 124.88 +/- 18,99; obese 120.70 +/-18.55 ml/min/1.73 m2; p<0.001). In addition, linear regression analysis has also revealed that eGFR decreased with higher BMI group (p<0.001):
eGFR (ml/min/1.73 m2): 126.57 + [0.57 x age (years)] - [2.52 x BMI groups] - [2.00 x living area]
where BMI groups are 1: underweight; 2: normal BMI; 3: overweight; 4: obese and living area groups are 1: urban and 2: rural area.
Regarding the new equations; I am afraid the validation studies are performed in children with CKD, but not in general population; i.e. healthy children [4-6]. Moreover, when we used new Schwartz formula: 0.413 x length (cm)/creatinine (mg/dL) [4], more than 15% of our study population would have an eGFR <75 ml/min/1.73 m2, which is not acceptable. We had mentioned in the discussion that eGFR based on a single creatinine measurement and absence of imaging studies are the limitations of our study.
References 1. Duzova A, Yalcinkaya F, Baskin E et al. Prevalence of hypertension and decreased glomerular filtration rate in obese children: results of a population-based field study. Nephrol Dial Transplant 2013;28 Suppl 4:iv166-171. 2. Schwartz GJ, Gauthier B. A simple estimate of glomerular filtration rate in adolescent boys. J Pediatr 1985;106:522-526. 3. Schwartz GJ, Haycock GB, Edelmann CM Jr et al. A simple estimate of glomerular filtration rate in children derived from body length and plasma creatinine. Pediatrics 1976;58:259-263. 4. Schwartz GJ, Munoz A, Schneider MF et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol 2009;20:629-637. 5. Schwartz GJ, Work DF. Measurement and estimation of GFR in children and adolescents. Clin J Am Soc Nephrol 2009;4:1832-1843. 6. Blufpand HN, Westland R, van Wijk JA et al. Height-independent estimation of glomerular filtration rate in children: an alternative to the Schwartz equation. J Pediatr 2013;163:1722-1727.
Conflict of Interest:
None declared
Duzova et al. presented the association between obesity and hypertension or estimated glomerular filtration rate (eGFR) among children in Turkey [1]. The authors mentioned that they used original Schwartz formula, which was expressed by height (cm)/serum creatinine multiplied by coefficient "k". They set k=0.7, when the target subject was male aged 13 or older, and 0.5 was adopted in other situations. The Schwartz formula was first reported in 1976 to estimate GFR in children [2]. Thereafter, a revised version for adolescent boys aged 13 or higher was presented [3]. As this formula overestimates GFR, a new equation was reported [4,5], and a validation study was also conducted [6].
I have a query about their method for calculating eGFR. In reference 3, it is described that eGFR is dependent on age, and age adjustment as "1.5xage+0.5x(height/serum creatinine)" presents a better estimation than "0.7x(height/serum creatinine)". I conducted a simple simulation study and the formula with k=7 presented a higher eGFR than with the age-adjusted formula, in subjects under the age of 20 with a serum creatinine<1.1 mg/dL and height>160cm. Duzova et al. reported that an increase in age presented a decreased risk of obesity in adolescent periods. I recommend the authors to conduct a logistic regression analysis by using age-adjusted eGFR for predicting obesity.
References
1. Duzova A, Yalcinkaya F, Baskin E et al. Prevalence of hypertension and decreased glomerular filtration rate in obese children: results of a population-based field study. Nephrol Dial Transplant 2013;28 Suppl 4:iv166-171.
2. Schwartz GJ, Haycock GB, Edelmann CM Jr et al. A simple estimate of glomerular filtration rate in children derived from body length and plasma creatinine. Pediatrics 1976;58:259-263.
3. Schwartz GJ, Gauthier B. A simple estimate of glomerular filtration rate in adolescent boys. J Pediatr 1985;106:522-526.
4. Schwartz GJ, Munoz A, Schneider MF et al. New equations to estimate GFR in children with CKD. J Am Soc Nephrol 2009;20:629-637.
5. Schwartz GJ, Work DF. Measurement and estimation of GFR in children and adolescents. Clin J Am Soc Nephrol 2009;4:1832-1843.
6. Blufpand HN, Westland R, van Wijk JA et al. Height-independent estimation of glomerular filtration rate in children: an alternative to the Schwartz equation. J Pediatr 2013;163:1722-1727.
Conflict of Interest:
None declared