Abstract
Background
The prevalence of urolithiasis and its risk factors such as obesity and diabetes have increased over time.
Objective
Determine the future cost and prevalence of kidney stones using current and projected estimates for stones, obesity, diabetes, gender, and population rates.
Design, Setting, and participants
The Stone prevalence in 2000 was estimated from National Health and Nutrition Examination Survey (NHANES) 1988–1994 and 2007–2010. The cost per percent prevalence of stone disease in 2000, calculated using Urologic Diseases in America Project data, was used to estimate the annual cost of stones in 2030, adjusting for inflation and increases in population, stone prevalence, obesity, and diabetes rates.
Outcome measurements and statistical analysis
The primary outcome was prevalence and cost of stones in 2030. The secondary outcomes were the impact of obesity and diabetes on these values, calculated using ratios for stones by body mass index and diabetes status.
Results and limitations
The annual cost of stone disease in 2000, adjusted for inflation to 2014 US dollars, was approximately $2.81 billion. After accounting for increased in population and stone prevalence from 2000, the estimated cost of stones in 2007 in 2014 US dollars was $3.79 billion. Future population growth alone would increase the cost of stone disease by $780 million in 2030. Based on projected estimates for 2030, obesity will independently increase stone prevalence by 0.36%, with an annual cost increase of $157 million. Diabetes will independently increase stone prevalence by 0.72, associated with a cost increase of $308 million annually by 2030. NHANES data, however, capture patient self-assessment rather than medical diagnosis, which is a potential bias.
Conclusions
The rising prevalence of obesity and diabetes, together with population growth, is projected to contribute to dramatic increases in the cost of urolithiasis, with an additional $1.24 billion/yr estimated by 2030.
Patient Summary
Obesity, diabetes, and population rates will contribute to an estimated $1.24 billion/yr increases in the cost of kidney stones by 2030.
Keywords: urolithiasis, cost, obesity, diabetes
1. Introduction
An assessment of the National Health and Nutrition Examination Survey (NHANES) II and III datasets revealed that the prevalence of kidney stones in US adults rose significantly, from 3.2% in 1976–1980 to 5.2% in 1988–19941. This trend has persisted with the latest NHANES data revealing an estimated 8.8% prevalence of stone disease2.
The concomitant rise in comorbid conditions associated with stone disease, including obesity and type 2 diabetes mellitus, has been proposed as a possible explanation for the rise in stone prevalence. In US adults, the prevalence of obesity increased from 30.5% in 2000 to 35.7% in 20103, and the age-adjusted prevalence of diabetes rose from 4.5% in 1995 to 8.2% in 20104. Both conditions have been linked to an increased risk of uric acid and calcium oxalate stone formation by a variety of proposed pathophysiologic mechanisms5–11.
Several studies have verified the positive association between body size and risk of stone formation2,12–15. In addition, obese first-time stone formers have been shown to have an increased incidence of stone recurrence and a decreased time to recurrence compared to nonobese first-time stone formers16.
The associations between obesity, diabetes and nephrolithiasis have been well established and the pathophysiologic mechanisms are currently being studied, but the impact of these comorbid conditions on cost and prevalence of stone disease has yet to be explored. In 2000 the total annual expenditure for urolithiasis was estimated at $2.1 billion, representing a 50% increase from estimates in 199417. The effect of obesity and diabetes on nephrolithiasis is likely to escalate the financial burden of this increasingly common condition. The aim of the present study was to calculate the effects of population, obesity, and diabetes on future costs of nephrolithiasis, specifically in the year 2030, using current and projected prevalence estimates of obesity, diabetes, population, and stone disease.
2. Methods
This study was exempt from review by our institutional review board because it does not include patient data.
2.1 Prevalence of stone disease in 2000
Because cost estimates for urolithiasis in the US have been reported for the year 2000, cost and estimated prevalence of stone disease from that year were used to derive the cost per unit percentage prevalence that could then be applied to a year for which we had prevalence but no cost data. Since no available national prevalence data spanned the year 2000, the prevalence of stones for that year was estimated by calculating the mean stone prevalence for the 1988–19941 and the 2007–20102 NHANES datasets. NHANES is a nationally representative, multistage probability survey assessing the health and nutritional status of the noninstitutionalized US population. Since there are more women than men in the United States, the stone prevalence was corrected for gender distribution (Table 1)18.
Table 1.
Lifetime stone prevalence and total annual cost of stone disease adjusting for population rates and gender distribution
| Percent prevalence of stone disease | |||
|---|---|---|---|
| Men | Women | Total Population | |
| NHANES 1988–19941 | 6.3 | 4.1 | 5.2 |
| NHANES 2007–20102 | 10.6 | 7.1 | 8.8 |
| Year 2000 (estimated) | 8.5 | 5.6 | 7.0* |
| Calculated Values | Total Annual Cost | ||
| Cost of stone disease in the US in 2000 (UDA data17) | $2,067,400,000 | ||
| Estimated cost per 1% stone prevalence in 2000 | $2,067,400,000/0.0700505 =$295,129,942 | ||
| Estimated cost per 1% stone prevalence in 2013 dollars** | $295,129,942 × 1.3535 =$399,458,377 | ||
| Estimated cost of stone disease in 2000 in the US in 2013 dollars** | $2,067,400,000 × 1.3535 =$2,798,225,900 | ||
| Estimated cost of stone disease in 2007 in the US^ in 2013 dollars** | [$2798225900 × 1.0718] × 1.25988 $3,778,459,341 | ||
| Estimated cost of stone disease in 2030 in the US^^ in 2013 dollars** | [$2798225900 × 1.2920] × 1.25988 $4,554,683,824 | ||
2.2 Cost per percent prevalence of stone disease in 2014 US dollars
The estimated cost for the diagnosis and management of nephrolithiasis for the year 2000 was obtained using data from the Urologic Diseases in America Project17. This cost was divided by the estimated lifetime prevalence for stone disease in 2000 to determine the cost per unit percentage prevalence of stones for that year. Year 2000 costs were then converted to 2014 dollars using an inflation calculator based on the US government Consumer Products Index to provide contemporaneous values (Table 1).
2.3 Population Estimates
Using the US Census Bureau's Population Estimates Program, which estimates yearly population in the United States from current data on births, deaths and migration to update the most recent decennial census, the total US population, as well as the percentage of men and women, was determined for 200718, a year for which the most current stone prevalence has been published2. An estimate of cost increase based on the increase in population was then determined using prevalence of stone disease from 2007–2010 NHANES data2, adjusting for gender distribution18 (Table 1). Population projections for 2030 were obtained from the US Census Bureau19.
2.4 Impact of obesity on cost
The standard categories of body mass index (BMI) in kilograms per square meter, as defined by the Centers for Disease Control and Prevention (CDC), are normal (18.5–24.9 kg/m2), overweight (25.0–29.9 kg/m2), and obese (≥30.0 kg/m2)20. The distribution of normal, overweight, and obese individuals in 2007 was obtained from NHANES data. These distributions were applied to the prevalence of stone disease from 2007–2010 NHANES data and the odds ratios for stone prevalence by weight category (1=normal BMI, 1.29=overweight, and 1.55=obese)2 to calculate the percentage prevalence of stone disease based on anticipated 10% shift from normal to overweight BMI and overweight to obese BMI in the US population. This method was chosen because the CDC projects that >44% of US adults (approximately a 10% increases from current prevalence) will be obese by 203021. The CDC’s analysis is based on a model that projects that around 50% (95% confidence internal [CI], 45–55) of US adults will be obese by 2030(Table 2).
Table 2.
Prevalence and cost of stone disease by BMI category in the adult US population in 2007 and projected estimates for 2030
2.5 Diabetes Prevalence
The percentage of diagnosed and undiagnosed diabetes rates among individuals ≥20 yr in the United States in 2007 was obtained from the CDC's National Diabetes Mellitus Fact Sheets22. These estimates were derived from the 2003–2006 NHANES, the 2004–2006 National Health Survey, 2005 Indian Health Service data, and 2007 resident population estimates. The odds ratio for a history of stone disease associated with a diagnosis of diabetes, independent of BMI and gender was previously reported as 1.592. This value was used to calculate the percentage prevalence of stone disease in 2030 applying extrapolated estimates from previously published projections of diabetes prevalence by gender for 2030 (Table 3)23.
Table 3.
Prevalence and cost of stone diseases by diabetes rates in the adult US population in 2007 and projected estimates for 2030.
3. Results
The average lifetime prevalence of stone disease in 2000 was calculated as 7.0% (8.5% in men and 5.6% in women). Assuming an annual expenditure for stone disease in 2000 of approximately $2.1 billion17, the cost per percentage prevalence of stone disease in 2000 was approximately $295 million. After adjusting for 35.8% inflation from 2000 to 2014, the cost per percent prevalence of stone disease in 2014 US dollars was $401 million, and the total cost of stone disease in 2000 in 2014 US dollars was approximately $2.81 billion (Table 1).
The US population in 2000 was 281,421,90624. In 2007, the population grew to 301,621,157 and was composed of 50.7% women and 49.3% men18. The calculated cost of stone disease, accounting for the 1.07–fold increase in the population from 2000 to 2007 and a 1.26-fold increase in stone prevalence from the calculated estimate in 2000 to the NHANES estimate for 2007–20102, resulted in an annual cost of $3.79 billion for stone disease in 2007, a year included in the most current available stone prevalence for US adults. The US Census Bureau estimate for the 2030 US population is 363,584,435, representing a 1.29 increase from 2000, which would be associated with an annual cost of stone disease of $4.57 billion in the unlikely event that stone prevalence remained constant from 2007 to 2030. Therefore, population growth alone is expected to increase the annual cost of stone disease by $776 million from current estimates by the year 2030 (Figure 1).
Figure 1.
Cost of stone disease in 2007 and the future based on obesity, diabetes, and population growth
After adjusting for gender distribution, the prevalence of stone disease in 2007 was 8.8%2. As shown in Table 2, we project a total lifetime prevalence of stone disease of 9.2% (95% CI, 8.3–10.1) if there is a 10% shift in normal weight to overweight and overweight to obese in men and women in the United States, as expected by 203025.
This change in obesity prevalence alone would result in a 0.36% absolute increase in stone prevalence by 2030. As such, for every 10% increase in obesity, the annual cost of stone disease is expected to be $3.95 billion (95% CI, 3.55 billion to 4.34 billion) representing a $157 million increase from 2007 to 2030 (Figure 1).
Table 3 shows that in 2007, the total reported prevalence of diagnosed and undiagnosed diabetes in adults ≥20 yr was estimated at 11.2% for US men and 10.2% for US women22. A 1.59-fold higher prevalence of urolithiasis has been reported among individuals with diabetes compared to nondiabetic individuals2. Using this odds ratio, we estimate that if the prevalence of diabetes increases as projected23, this factor alone will independently increase stone prevalence to 9.5% (95% CI, 3.62–4.58), representing an increase of $308 million by 2030(Figure 1).
Taking into account the projected increase in population, diabetes and obesity, the increase in the total cost of stone disease from 2007 to 2030 will be $1.24 billion in 2014 US dollars, without taking into account other factors that influence stone prevalence.
4. Discussion
This analysis represents the first published attempt to quantify the effects of population growth and rising rates obesity, and diabetes on the prevalence and cost of stone disease. In addition, projected future costs that might be incurred as a result of population growth and increasing prevalence of these comorbid conditions are described in this paper. We chose to project estimates for 2030, a year in the near future for which high-quality estimates of obesity and diabetes exist. We showed that population growth alone will have the most profound impact on increasing the annual cost of stone disease. The cost of stone disease in 2000 was approximately $2.1 billion annually17. After accounting for increases in population and stone prevalence from 2000, the estimated cost of stone disease in 2007 in 2014 US dollars was $3.79 billion. We calculated that in the unlikely event that stone prevalence remains unchanged from the last national published estimate2, the population growth expected by 2030 will independently increase the annual cost of stone disease by a staggering $ 780 million. Population growth is largely a nonmodifiable factor, but we showed that potentially modifiable factors such as obesity and diabetes are related to escalations in stone disease prevalence that contribute, though not as significantly as does population growth, to substantial increase in the cost associated with urolithiasis.
The data for much of our investigation are derived from the 2007 NHANES by Scales et al2, which represents the most recent assessment of kidney stone prevalence since Stamatelou and colleagues analyzed 1976–1994 NHANES data11. Because of established associations among obesity, diabetes, and stone disease, Scales and colleagues created multivariable models to quantify the independent relationship of these factors to stone disease and subsequently generated odds rations, which we used in our analysis.
The CDC released rates of current and future obesity in August 201225. Twelve states have an adult obesity rate exceeding >30%. If obesity continues at the current rate, the CDC projects that >44% of US adults (a 10% increase from current rates) will be obese by 2030. A 10% increase from normal to overweight and overweight to obese would independently account for an additional $157 million in annual cost of stone disease, based on our calculations.
We acknowledge that obesity and diabetes are interrelated entities, and therefore an increase in one will produce a concomitant increase in the other. However, the two conditions were independently associated with a greater prevalence of urolithiasis in the latest NHANES data set2. Therefore, the independent impact of diabetes on stone prevalence will likely still be realized, as a dramatic rise in the prevalence of diabetes – to nearly 1 in 10 US adults – is anticipated by 2030. We estimate that the independent effect of this projected rise in diabetes will increase the cost of stone disease by $73million by 2030.
Using projected estimates of population, obesity, and diabetes, we predict that the annual cost of stone disease will increase by 33% in the year 2030 totaling an additional $1.24 billion/yr annually, without taking into account other factors that influence stone prevalence. In any case, these figures are likely underestimated, since the cost of health care has outpaced inflation26.
The epidemiological literature supports the metabolic associations that have been demonstrated among obesity, diabetes, and stone formation. Curhan and coworkers showed that the prevalence and incidence of stone disease were positively associated with body weight and BMI12. Weight gain, a process that likely involves the addition of proportionally more adipose tissue compared with lean muscle, was associated with an increased rate of incident stone formation15. Semins and associates also examined the relationship between BMI and stones using claims data and found an increasing risk of kidney stones with increasing BMI up to a BMI of 30 kg/m2, after which the risk stabilized14.
Our estimates of the effects of obesity and diabetes on the prevalence and cost of stone disease would be incomplete without including the impact of population growth. When attempting to consolidate the individual contribution of obesity, diabetes, and population change on stone disease, the magnitude of each has to be weighted. Although the published odds ratios for diabetes and obesity provided this information for the analysis of current prevalence and cost estimates2, any projected future estimates must take into account the rate of change of each factor. In addition, the incidence of stones peaks in the fourth to sixth decade of life27. As such, the direct and indirect costs of stone disease in this working age group are substantial28. While an age-stratified analysis could provide insight into cost contributions of certain subgroups of the population, this level of data granularity for specific age groups was lacking and precluded this type of analysis. The majority of population gains in the future will be in older segments of the population.
Although this analysis represents the first estimate of the impact of population growth, obesity and diabetes on current and future costs of stone disease, our results must be tempered by some inherent limitations. First the NHANES instrument from which we derived much of our data is a cross-sectional design that uses patient self-assessment of stone disease and not confirmed medical diagnoses. Scales et al also recognized this limitation in their analysis and additionally considered a secondary outcome of self-reported stone passage that reflected symptomatic stones and found similar results regarding stone prevalence2. Any prevalence data are limited by the inability to diagnose asymptomatic stones. In addition to NHANES, we used data derived from several other large databases, which leads to inherent bias. Finally, our analysis failed to take into account other important demographic factors, such as race/ethnicity, geography, and socioeconomic status, that may change unpredictably over time and effect stone prevalence independently, as well as rates of diabetes and obesity. The incorporation of these variables into future analyses will provide a more fine-tuned estimate of current and future costs.
5. Conclusions
In this paper we present a sound analysis of the most current data regarding stone prevalence, obesity, diabetes, and population changes and their effects on cost both today and in the future. Obesity and diabetes are somewhat modifiable diseases that affect stone prevalence, and as demonstrated in this paper, their rising incidence, in conjunction with population growth, will lead to substantial increases in future stone-related health care costs.
Acknowledgments
Funding/Support: None
References
- 1.Stamatelou KK, Francis ME, Jones CA, Nyberg LM, Curhan GC. Time trends in reported prevalence of kidney stones in the United States: 1976–1994. Kidney international. 2003 May;63(5):1817–1823. doi: 10.1046/j.1523-1755.2003.00917.x. [DOI] [PubMed] [Google Scholar]
- 2.Scales CD, Jr, Smith AC, Hanley JM, Saigal CS Urologic Diseases in America P. Prevalence of kidney stones in the United States. European urology. 2012 Jul;62(1):160–165. doi: 10.1016/j.eururo.2012.03.052. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3.Ogden CL, Carroll MD, Kit BK, Flegal KM. Prevalence of obesity in the United States, 2009–2010. NCHS data brief. 2012 Jan;(82):1–8. [PubMed] [Google Scholar]
- 4.Centers for Disease Control and Prevention. Increasing prevalence of diagnosed diabetes--United States and Puerto Rico, 1995–2010. MMWR. Morbidity and mortality weekly report. 2012 Nov 16;61(45):918–921. [PubMed] [Google Scholar]
- 5.Abate N, Chandalia M, Cabo-Chan AV, Jr, Moe OW, Sakhaee K. The metabolic syndrome and uric acid nephrolithiasis: novel features of renal manifestation of insulin resistance. Kidney international. 2004 Feb;65(2):386–392. doi: 10.1111/j.1523-1755.2004.00386.x. [DOI] [PubMed] [Google Scholar]
- 6.Cameron MA, Maalouf NM, Adams-Huet B, Moe OW, Sakhaee K. Urine composition in type 2 diabetes: predisposition to uric acid nephrolithiasis. Journal of the American Society of Nephrology : JASN. 2006 May;17(5):1422–1428. doi: 10.1681/ASN.2005121246. [DOI] [PubMed] [Google Scholar]
- 7.Cupisti A, Meola M, D'Alessandro C, et al. Insulin resistance and low urinary citrate excretion in calcium stone formers. Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie. 2007 Jan;61(1):86–90. doi: 10.1016/j.biopha.2006.09.012. [DOI] [PubMed] [Google Scholar]
- 8.DuBose TD, Jr, Good DW, Hamm LL, Wall SM. Ammonium transport in the kidney: new physiological concepts and their clinical implications. Journal of the American Society of Nephrology : JASN. 1991 May;1(11):1193–1203. doi: 10.1681/ASN.V1111193. [DOI] [PubMed] [Google Scholar]
- 9.Maalouf NM, Cameron MA, Moe OW, Sakhaee K. Metabolic basis for low urine pH in type 2 diabetes. Clinical journal of the American Society of Nephrology : CJASN. 2010 Jul;5(7):1277–1281. doi: 10.2215/CJN.08331109. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 10.Maalouf NM, Sakhaee K, Parks JH, Coe FL, Adams-Huet B, Pak CY. Association of urinary pH with body weight in nephrolithiasis. Kidney international. 2004 Apr;65(4):1422–1425. doi: 10.1111/j.1523-1755.2004.00522.x. [DOI] [PubMed] [Google Scholar]
- 11.Sakhaee K, Maalouf NM. Metabolic syndrome and uric acid nephrolithiasis. Seminars in nephrology. 2008 Mar;28(2):174–180. doi: 10.1016/j.semnephrol.2008.01.010. [DOI] [PubMed] [Google Scholar]
- 12.Curhan GC, Willett WC, Rimm EB, Speizer FE, Stampfer MJ. Body size and risk of kidney stones. Journal of the American Society of Nephrology : JASN. 1998 Sep;9(9):1645–1652. doi: 10.1681/ASN.V991645. [DOI] [PubMed] [Google Scholar]
- 13.Nowfar S, Palazzi-Churas K, Chang DC, Sur RL. The relationship of obesity and gender prevalence changes in United States inpatient nephrolithiasis. Urology. 2011 Nov;78(5):1029–1033. doi: 10.1016/j.urology.2011.04.011. [DOI] [PubMed] [Google Scholar]
- 14.Semins MJ, Shore AD, Makary MA, Magnuson T, Johns R, Matlaga BR. The association of increasing body mass index and kidney stone disease. The Journal of urology. 2010 Feb;183(2):571–575. doi: 10.1016/j.juro.2009.09.085. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 15.Taylor EN, Stampfer MJ, Curhan GC. Obesity, weight gain, and the risk of kidney stones. JAMA : the journal of the American Medical Association. 2005 Jan 26;293(4):455–462. doi: 10.1001/jama.293.4.455. [DOI] [PubMed] [Google Scholar]
- 16.Lee SC, Kim YJ, Kim TH, Yun SJ, Lee NK, Kim WJ. Impact of obesity in patients with urolithiasis and its prognostic usefulness in stone recurrence. The Journal of urology. 2008 Feb;179(2):570–574. doi: 10.1016/j.juro.2007.09.040. [DOI] [PubMed] [Google Scholar]
- 17.Pearle MS, Calhoun EA, Curhan GC. Urologic diseases in America project: urolithiasis. The Journal of urology. 2005 Mar;173(3):848–857. doi: 10.1097/01.ju.0000152082.14384.d7. [DOI] [PubMed] [Google Scholar]
- 18.Population Division, US Census Bureau. Annual estimates of the population by sex and five-year age groups for the United States. 2008 [Google Scholar]
- 19.US Census Bureau. 2005 interim state population projections (Table 6) 2005 [Google Scholar]
- 20.National Institutes of Health. Clinical Guidelines on the identification, evaluation, and treatment of overwight and obesity in adults- the evidence report. Obes Res. 1998;51(Suppl 6):2095. [PubMed] [Google Scholar]
- 21.Flegal KM, Carroll MD, Ogden CL, Curtin LR. Prevalence and trends in obesity among US adults, 1999–2008. Jama. 2010 Jan 20;303(3):235–241. doi: 10.1001/jama.2009.2014. [DOI] [PubMed] [Google Scholar]
- 22.Centers for Disease Control and Prevention. National diabetes fact sheet:general information and national estimates on diabetes in the United States. US Department of Health and Human Services, Centers for Disease Control and Prevention 2008. 2007 [Google Scholar]
- 23.Boyle JP, Thompson TJ, Gregg EW, Barker LE, Williamson DF. Projection of the year 2050 burden of diabetes in the US adult population: dynamic modeling of incidence, mortality, and prediabetes prevalence. Population health metrics. 2010;8:29. doi: 10.1186/1478-7954-8-29. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 24.US Census Bureau 2000 census of population and housing: population and housing unit counts PHC-31-1. United States Summary. 2000 [Google Scholar]
- 25.Levi JSL, St. Laurent R, Lang A, rAYBURN j. F as in fat. How obesity threatens Americas future. Trust for Americas Health/Robert Wood Johnson Foundation 2012. 2012 [Google Scholar]
- 26.Kumar S, Ghildayal NS, Shah RN. Examining quality and efficiency of the U.S. healthcare system. International journal of health care quality assurance. 2011;24(5):366–388. doi: 10.1108/09526861111139197. [DOI] [PubMed] [Google Scholar]
- 27.Johnson CM, Wilson DM, O'Fallon WM, Malek RS, Kurland LT. Renal stone epidemiology: a 25-year study in Rochester, Minnesota. Kidney international. 1979 Nov;16(5):624–631. doi: 10.1038/ki.1979.173. [DOI] [PubMed] [Google Scholar]
- 28.Saigal CS, Joyce G, Timilsina AR Urologic Diseases in America P. Direct and indirect costs of nephrolithiasis in an employed population: opportunity for disease management? Kidney international. 2005 Oct;68(4):1808–1814. doi: 10.1111/j.1523-1755.2005.00599.x. [DOI] [PubMed] [Google Scholar]