Urinary Albumin Excretion as a Predictor of the Development of Hypertension in the General Population
Auke H. Brantsma*,
Stephan J.L. Bakker,,
Dick de Zeeuw*,,
Paul E. de Jong*,
Ronald T. Gansevoort* for the PREVEND Study Group
* Division of Nephrology; Department of Medicine; and Department of Clinical Pharmacology, University Medical Center Groningen, University of Groningen, Groningen, The Netherlands
Address correspondence to: Dr. Ronald T. Gansevoort, Division of Nephrology, Department of Medicine, University Medical Center Groningen, PO Box 30.001, Groningen, 9700 RB The Netherlands. Phone: +31-50-3616161; Fax: +31-50-3619310; r.t.gansevoort{at}int.umcg.nl
The hypothesis that high urinary albumin excretion (UAE; indicatingmild renal damage) may precede development of hypertension wastested, and the relation among UAE, GFR, and development ofhypertension was investigated. Data of 4635 patients of a prospectivecohort study who participated in an extensive screening in 1997to 1998 and 2001 to 2003 at our outpatient unit and were normotensiveat baseline were used. Hypertension was defined according tothe Seventh Report of the Joint National Committee on Prevention,Detection, Evaluation, and Treatment of High Blood Pressurecriteria, UAE was measured in two consecutive 24-h urine samples,and GFR was calculated with the modified Modification of Dietin Renal Disease formula. Mean follow-up was 4.3 yr. BaselineUAE was significantly associated with the risk for developinghypertension (odds ratio 2.29; 95% confidence interval 1.77to 2.95 per 10-fold increase of UAE). This association was independentof potential confounders. An interaction between UAE and GFRwas found (P = 0.030), indicating that with elevated UAE andlowered GFR, but still within the normal range, the risk fordeveloping hypertension was highest. In conclusion, these findingssupport the hypothesis that mild renal damage may precede thedevelopment of hypertension.
BP is thought to be an important determinant of developmentof high urinary albumin excretion (UAE), an early marker ofrenal damage (13). However, experimental data showedthat subtle renal damage in normotensive rats leads to the developmentof salt-sensitive hypertension (46). This suggests thatinstead of being a consequence of high BP, mild renal damageand, consequently, high UAE also may precede development ofhypertension. This is in line with the hypothesis proposed byGoldblatt (7) more than 50 yr ago. On the basis of the observationthat in hypertensive individuals arteriolosclerosis of the kidneysis nearly universal but in other organs occurs only in a minorityof patients, he suggested that renal damage precedes the developmentof hypertension. Indeed, this is seen clearly in patients withsevere renal impairment, in whom disturbances in volume homeostasismay cause hypertension (1). However, the relation between mildrenal damage and development of hypertension in humans is stillunknown. We therefore investigated whether an increase in UAEmay precede development of hypertension and whether this isdue to the association of UAE with renal damage, using a large,community-based, prospective cohort study.
Study Design and Population
This study is part of the ongoing PREVEND study (Preventionof REnal and Vascular ENd stage Disease), a large prospectivecohort study that is investigating the predictive value of UAEfor renal and cardiovascular disease progression. The patientsof the PREVEND cohort were selected in 1997 from 40,856 individualsfrom the general population. Selection was based on their albuminconcentration in a spot morning urine sample to enrich the cohortfor the presence of albuminuria. In total, 8592 individualscompleted the first survey (1997 to 1998) (8,9). During follow-up,240 individuals died and 1458 individuals declined participation.Thus, 6894 individuals completed the second survey (2001 to2003). We used data of the 4635 individuals who did not havehypertension (n = 2247) or self-reported renal disease (n =12) at baseline and participated in the first and second surveys.The PREVEND study is approved by the medical ethics committeeof our institution and conducted in accordance with the guidelinesof the declaration of Helsinki. All participants gave writteninformed consent.
Measurements and Definitions
For each screening, participants completed two visits at ouroutpatient unit. Height, weight, and waist circumference weremeasured. Participants completed a questionnaire on demographics,cardiovascular and renal disease history, and use of medicationfor hypertension. Information on drug use was complemented withdata from community pharmacies. During the first and secondvisits, BP was measured at the right arm, in supine position,every minute for 10 and 8 min, respectively, with an automaticdevice (Dinamap XL Model 9300; Johnson-Johnson Medical, Tampa,FL). Two 24-h urine samples were collected after thorough oraland written instructions on how to perform a urine collection,and a fasting blood sample was drawn. Standard 12-lead electrocardiogramswere recorded with Cardio Perfect equipment (Cardio Control,Rijswijk, The Netherlands) and stored digitally using the computerprogram MEANS (Modular Electrocardiogram ANalysis System).
Urinary albumin concentration was determined by nephelometry(BNII; Dade Behring Diagnostic, Marburg, Germany). UAE is givenas the mean of the two 24-h urine excretions. Concentrationsof sodium, high-sensitivity C-reactive protein (hs-CRP), creatinine,total cholesterol, triglycerides, insulin, and glucose weremeasured in serum or urine using standard methods.
BP values are given as the mean of the last two recordings ofboth visits. Hypertension was defined as a systolic BP (SBP)of 140 mmHg and/or a diastolic BP (DBP) of 90 mmHg and/or theuse of antihypertensive medication according to the SeventhReport of the Joint National Committee on Prevention, Detection,Evaluation, and Treatment of High Blood Pressure guidelines(10). GFR was estimated with the modified Modification of Dietin Renal Disease formula, taking into account gender, age, race,and serum creatinine concentration (1). Sodium intake was estimatedwith 24-h urinary sodium excretion. Participants were definedas smoking when they had smoked regularly in the previous year.Increased alcohol use was defined as drinking >3 glasses/d.Left ventricular hypertrophy (LVH) was identified using theCornell voltage-duration product, calculated as R wave fromaVL lead (RaVL) + S wave from V3 lead (SV3) (with 6 mm addedin women) times QRS duration. A threshold of 2440 mm/ms wasused to identify LVH (11).
Statistical Analyses
Analyses were performed using the statistical package SPSS 12.0(SPSS, Chicago, IL). The level of significance was determinedas P < 0.05. Continuous data are reported as mean with SDor as median and interquartile range in case of a skewed distribution.Prevalence and incidence are presented as percentages. Differencesbetween groups were tested by a t test or a Mann-Whitney ranktest for continuous data with a normal or skewed distribution,respectively. Differences in prevalence or incidence were testedwith a 2 test. To test for trends in ordinal data, we used theMantel-Haenszel 2 test for trend.
The predictive value of UAE was tested in logistic regressionmodels with development of hypertension as dependent variable.Logarithmic transformation (Ln) of UAE, hs-CRP, insulin, andtriglycerides was applied in logistic regression analysis tofulfill the requirement of linearity in the logit. The finalmultivariate model was tested for interactions. Interactionswere considered significant at P < 0.1. Models were testedfor tolerance to colinearity with methods described by Hosmeret al. (12). Data of logistic regression analysis are givenas odds ratio (OR) and 95% confidence interval (CI).
We observed 19592 person-years during a mean follow-up of 4.2yr. In this time, 413 (8.9%) participants of our populationdeveloped hypertension, giving an incidence rate of 21/1000person-years. Compared with participants who remained normotensiveduring follow-up, participants who developed hypertension weregenerally older, with an unfavorable cardiovascular risk profile,including higher SBP and DBP and decreased GFR (Table 1). UAEwas increased in participants who developed hypertension. Accordingly,the incidence of hypertension was higher with higher baselinelevels of UAE (Figure 1).
Figure 1. Baseline urinary albumin excretion (UAE) and incidence of hypertension after 4.2 yr of follow-up. Incidence is given according to clinical categories of UAE at baseline (P < 0.001 for trend). Numbers in the bars indicate the number of individuals within the category. When we subdivided the population according to tertiles of UAE at baseline (<6.5, 6.5 to 10.5, and >10.5, respectively), a similar trend was seen, with an incidence of hypertension of 6.5, 8.3, and 11.9% from the lowest to the highest tertiles, respectively (P < 0.001 for trend).
When baseline UAE was entered in a logistic regression modelwith hypertension as dependent variable, UAE significantly predicteddevelopment of hypertension with an OR of 1.43 (95% CI 1.28to 1.60) per 1 Ln(UAE) unit of change. This equals an OR of2.29 (95% CI 1.77 to 2.95) for each 10-fold increase of UAE.After adjustment for age and gender; baseline values of SBP,DBP, and GFR; and other possible confounders, the associationbetween UAE and the development of hypertension remained significant(Table 2).
Table 2. Logistic regression models with development of hypertension after 4.2 yr of follow-up as dependent variablea
In the final model, a significant interaction was found betweenUAE and GFR (Table 2, model 5). To explore this interaction,we repeated our final model in strata according to tertilesof GFR. Results for UAE in the three strata of GFR were OR 1.93(95% CI 1.26 to 2.97), OR 0.84 (95% CI 0.41 to 1.71), and OR1.16 (95% CI 0.54 to 2.49) per 10-fold increase of UAE in thelowest to highest tertiles, respectively. The interaction betweenUAE and GFR is illustrated in Figure 2. This graph shows thatUAE predicts the development of hypertension most strongly whenrenal function is low, indicating synergism. When renal functionis higher, the risk that is added by an increased UAE diminishes.
Figure 2. Incidence of hypertension after 4.2 yr of follow-up by categories of albuminuria and tertiles of GFR at baseline.
These findings are in contrast with current thinking that elevatedUAE is secondary to development of high BP (2,10). One couldargue that our observation is erroneous and caused by the presenceof prehypertension in individuals with high UAE at baselineor by misclassification of individuals as normotensive at baselineas a result of variation in the BP measurement, whereas in factthey were hypertensive. Therefore, we first adjusted our modelsfor baseline SBP and DBP. After these adjustments, the associationbetween UAE and development of hypertension remained significant.Second, we repeated our analyses after adjustment for the presenceof LVH at baseline. LVH is considered a marker of target organdamage in hypertensive individuals (2,10) and might indicatethe presence of prehypertension or undiagnosed hypertensionin individuals who are classified as normotensive. However,adjustment for the presence of LVH did not influence our findingthat baseline UAE predicts the development of hypertension.Third, we excluded participants who had an SBP 135 and/or DBP85 (n = 505) at baseline. This cutoff point was chosen to excludeindividual who had the highest risk for being prehypertensiveor misclassified as normotensive while maintaining an adequatenumber of cases. Again, this correction did not affect our results.Thus, our study shows that UAE predicts future development ofhypertension, independent of other predisposing factors. Theincreased risk for hypertension associated with elevated UAEis higher when the GFR is lower.
Our results confirm the finding in the Framingham OffspringStudy that urinary albumin concentration in a single morningvoid urine sample is associated with the risk for developinghypertension (13). However, in contrast to our study, the FraminghamOffspring Study did not explicitly investigate the relationamong UAE, renal function, and development of hypertension.Although the authors added to their statistical model baselineserum creatinine as a renal parameter to adjust for possibleconfounding by the presence of renal dysfunction, the use ofserum creatinine as an estimate of renal function is not recommended(1,14). It is generally accepted that the inverse relation betweenserum creatinine and GFR is influenced by muscle mass and consequentlyby factors such as age, gender, and race. These factors shouldbe taken into account using a validated formula.
The finding that baseline UAE predicts BP progression has beendebated by the investigators of the HARVEST Study, who werenot able to demonstrate such a relation (15,16). This conflictingdata may be explained by the lower age of the population inthe HARVEST Study (mean age 33 yr), compared with the age ofour population (mean age 45 yr) or the population of the FraminghamOffspring Study (mean age approximately 55 yr). A differentmechanism may underlie the development of UAE in this youngage group with low cardiovascular risk, with UAE for instancebeing more hemodynamically related, whereas UAE may be moreassociated with renal microvascular damage in the older agegroups with higher cardiovascular risk.
We explain our findings as follows. Both lower GFR and higherUAE can have renal damage as the underlying cause (1). Thus,the presence of an interaction between these two variables inour model suggests that UAE predicts the development of hypertensionas a result of the underlying presence of mild renal damage.It has been well established that the kidney plays a centralrole in the pathogenesis of hypertension in case of severe renalfunction impairment (1,17,18), but even in individuals withmild renal damage, this may be the case. Recent experimentalstudies in rats have shown that minor changes in the renal microvasculatureand tubulointerstitium may lead to salt-sensitive hypertension(46), providing a possible pathway whereby mild renaldamage can lead to the development of hypertension (19). Furthermore,as hypothesized by Brenner et al. (20), a reduction in glomerularfiltration surface area, which may be reflected by a mildlyreduced GFR, may lead to hypertension as a result of a limitedability to excrete sodium. Indeed, a recent autopsy study suggestedthat young hypertensive individuals may have a lower numberof nephrons than age-matched normotensive control subjects (21),supporting Brenners hypothesis.
Although the studies mentioned above underscore the importanceof the kidney in the pathogenesis of hypertension, the causeof hypertension is heterogeneous. UAE is suggested to be theresult of damage to the renal microvasculature (1,22), but theselocal changes in turn may be part of generalized endothelialdysfunction (23). Indeed, generalized endothelial dysfunctionhas been suggested to play a role in the cause of hypertension(24,25). Thus, alternatively, the association between UAE andgeneralized endothelial dysfunction could explain our findings.To test for this possibility, we looked at the effect of hs-CRPon the association among UAE, renal function, and the developmentof hypertension in our logistic regression models, because hs-CRPhas also been found to be associated with generalized endothelialdysfunction (2628). Although baseline hs-CRP was univariatelysignificantly associated with development of hypertension duringfollow-up (OR 1.24; 95% CI 1.17 to 1.32 per two-fold changeof hs-CRP; P < 0.001), in the multivariate models, afteradjustment for possible confounders, this association was nolonger significant (final model P = 0.3). Furthermore, the presenceof hs-CRP in the model did not influence the association amongUAE, renal function, and the development of hypertension. Thus,in our opinion, it is less likely that the association of UAEwith generalized endothelial dysfunction explains our findings.
Strengths of our study are the use of a large community-basedcohort, use of 24-h urine samples to estimate UAE, use of dataof community pharmacies to complement self-reported data onuse of antihypertensive drugs, extensive adjustment for covariatesthat are associated with development of hypertension, and thepossibility to explore different possible pathways to explainthe association between UAE and the development of hypertension.Two limitations should be mentioned. First, the PREVEND cohortis selected from a mainly white population. Our findings thereforecannot simply be generalized to other populations. Second, almost20% of the participants of our baseline cohort died or werenot willing to participate during follow-up. Although the differencesbetween baseline characteristics of individuals with follow-upand individuals who were lost to follow-up were numericallysmall (data not shown), we cannot exclude that survival biaswas introduced. However, because individuals with high UAE,lower GFR, or hypertension are more likely to be lost duringfollow-up as a result of the associated increased morbidityand mortality, it is likely that such a bias has led to an underestimationof the true association among UAE, GFR, and development of hypertension.
We conclude from this prospective, community-based cohort studythat UAE predicts the development of hypertension, independentof BP and other widely known risk factors for development ofhypertension. Our study suggests that this is explained by theassociation of UAE with mild renal dysfunction. This study thereforegives epidemiologic evidence in support of the hypothesis thatmild renal dysfunction may precede the onset of systemic hypertension.
Acknowledgments
A.H.B. and R.T.G. had full access to all of the data in thestudy and take responsibility for the integrity of the dataand the accuracy of the data analysis.
We thank Dade Behring (Marburg, Germany) for supplying equipment(Behring Nephelometer II) and reagents for nephelometric measurementof urinary albumin. We acknowledge the assistance of J. vander Wal-Hanewald and J.J. Duker (laboratory assistants) forconcise and elaborate work.
Footnotes
Published online ahead of print. Publication date availableat www.jasn.org.
K/DOQI clinical practice guidelines for chronic kidney disease: Evaluation, classification, and stratification.
Am J Kidney Dis 39
: S1
S266, 2002[CrossRef][Medline]
2003 European Society of HypertensionEuropean Society of Cardiology guidelines for the management of arterial hypertension.
J Hypertens 21
: 1011
1053, 2003[CrossRef][Medline]
Bianchi S, Bigazzi R, Campese VM: Microalbuminuria in essential hypertension: Significance, pathophysiology, and therapeutic implications.
Am J Kidney Dis 34
: 973
995, 1999[Medline]
Andoh TF, Johnson RJ, Lam T, Bennett WM: Subclinical renal injury induced by transient cyclosporine exposure is associated with salt-sensitive hypertension.
Am J Transplant 1
: 222
227, 2001[CrossRef][Medline]
Mai M, Geiger H, Hilgers KF, Veelken R, Mann JF, Dammrich J, Luft FC: Early interstitial changes in hypertension-induced renal injury.
Hypertension 22
: 754
765, 1993[Abstract/Free Full Text]
Franco M, Tapia E, Santamaria J, Zafra I, Garcia-Torres R, Gordon KL, Pons H, Rodriguez-Iturbe B, Johnson RJ, Herrera-Acosta J: Renal cortical vasoconstriction contributes to development of salt-sensitive hypertension after angiotensin II exposure.
J Am Soc Nephrol 12
: 2263
2271, 2001[Abstract/Free Full Text]
Goldblatt H: The renal origin of hypertension.
Physiol Rev 27
: 120
165, 1947[Free Full Text]
Pinto-Sietsma SJ, Janssen WM, Hillege HL, Navis G, de Zeeuw D, de Jong PE: Urinary albumin excretion is associated with renal functional abnormalities in a nondiabetic population.
J Am Soc Nephrol 11
: 1882
1888, 2000[Abstract/Free Full Text]
Pinto-Sietsma SJ, Mulder J, Janssen WM, Hillege HL, de Zeeuw D, de Jong PE: Smoking is related to albuminuria and abnormal renal function in nondiabetic persons.
Ann Intern Med 133
: 585
591, 2000[Abstract/Free Full Text]
Chobanian AV, Bakris GL, Black HR, Cushman WC, Green LA, Izzo JL Jr, Jones DW, Materson BJ, Oparil S, Wright JT Jr, Roccella EJ: The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure: The JNC 7 report.
JAMA 289
: 2560
2572, 2003[Abstract/Free Full Text]
Dahlof B, Devereux R, de Faire U, Fyhrquist F, Hedner T, Ibsen H, Julius S, Kjeldsen S, Kristianson K, Lederballe-Pedersen O, Lindholm LH, Nieminen MS, Omvik P, Oparil S, Wedel H: The Losartan Intervention For Endpoint reduction (LIFE) in Hypertension study: Rationale, design, and methods. The LIFE Study Group.
Am J Hypertens 10
: 705
713, 1997[CrossRef][Medline]
Hosmer DW, Lemeshow S:
Applied Logistic Regression, 2nd Ed., New York, John Wiley & Sons, 2000
, pp 140
141
Wang TJ, Evans JC, Meigs JB, Rifai N, Fox CS, DAgostino RB, Levy D, Vasan RS: Low-grade albuminuria and the risks of hypertension and blood pressure progression.
Circulation 111
: 1370
1376, 2005[Abstract/Free Full Text]
Hsu CY, Chertow GM, Curhan GC: Methodological issues in studying the epidemiology of mild to moderate chronic renal insufficiency.
Kidney Int 61
: 1567
1576, 2002[CrossRef][Medline]
Palatini P: Letter regarding article by Wang et al, "Low-grade albuminuria and the risks of hypertension and blood pressure progression."
Circulation 112
: e121
1576, 2005[Free Full Text]
Palatini P, Mormino P, Mos L, Mazzer A, Dorigatti F, Zanata G, Longo D, Garbelotto R, De Toni R, Graniero G, Pessina AC: Microalbuminuria, renal function and development of sustained hypertension: A longitudinal study in the early stage of hypertension.
J Hypertens 23
: 175
182, 2005[CrossRef][Medline]
Cowley AW Jr, Roman RJ: The role of the kidney in hypertension.
JAMA 275
: 1581
1589, 1996[CrossRef][Medline]
Rettig R, Grisk O: The kidney as a determinant of genetic hypertension: Evidence from renal transplantation studies.
Hypertension 46
: 463
468, 2005[Free Full Text]
Johnson RJ, Herrera-Acosta J, Schreiner GF, Rodriguez-Iturbe B: Subtle acquired renal injury as a mechanism of salt-sensitive hypertension.
N Engl J Med 346
: 913
923, 2002[Free Full Text]
Brenner BM, Garcia DL, Anderson S: Glomeruli and blood pressure. Less of one, more the other?
Am J Hypertens 1
: 335
347, 1988[Medline]
Keller G, Zimmer G, Mall G, Ritz E, Amann K: Nephron number in patients with primary hypertension.
N Engl J Med 348
: 101
108, 2003[Abstract/Free Full Text]
Keane WF, Eknoyan G: Proteinuria, albuminuria, risk, assessment, detection, elimination (PARADE): A position paper of the National Kidney Foundation.
Am J Kidney Dis 33
: 1004
1010, 1999[Medline]
Rossi R, Chiurlia E, Nuzzo A, Cioni E, Origliani G, Modena MG: Flow-mediated vasodilation and the risk of developing hypertension in healthy postmenopausal women.
J Am Coll Cardiol 44
: 1636
1640, 2004[Abstract/Free Full Text]
Wong TY, Shankar A, Klein R, Klein BE, Hubbard LD: Prospective cohort study of retinal vessel diameters and risk of hypertension.
BMJ 329
: 79
1640, 2004[Abstract/Free Full Text]
Cleland SJ, Sattar N, Petrie JR, Forouhi NG, Elliott HL, Connell JM: Endothelial dysfunction as a possible link between C-reactive protein levels and cardiovascular disease.
Clin Sci (Lond) 98
: 531
535, 2000[Medline]
Teragawa H, Fukuda Y, Matsuda K, Ueda K, Higashi Y, Oshima T, Yoshizumi M, Chayama K: Relation between C reactive protein concentrations and coronary microvascular endothelial function.
Heart 90
: 750
754, 2004[Abstract/Free Full Text]
This article has been cited by other articles:
A. Friedman, D. Marrero, Y. Ma, R. Ackermann, K.M. V. Narayan, E. Barrett-Connor, K. Watson, W. C. Knowler, E. S. Horton, and for the Diabetes Prevention Program Research Group Value of Urinary Albumin-to-Creatinine Ratio as a Predictor of Type 2 Diabetes in Pre-Diabetic Individuals
Diabetes Care,
December 1, 2008;
31(12):
2344 - 2348.
[Abstract][Full Text][PDF]
P. E. de Jong and R. T. Gansevoort Fact or fiction of the epidemic of chronic kidney disease--let us not squabble about estimated GFR only, but also focus on albuminuria
Nephrol. Dial. Transplant.,
April 1, 2008;
23(4):
1092 - 1095.
[Full Text][PDF]
B. Kestenbaum, K. D. Rudser, I. H. de Boer, C. A. Peralta, L. F. Fried, M. G. Shlipak, W. Palmas, C. Stehman-Breen, and D. S. Siscovick Differences in Kidney Function and Incident Hypertension: The Multi-Ethnic Study of Atherosclerosis
Ann Intern Med,
April 1, 2008;
148(7):
501 - 508.
[Abstract][Full Text][PDF]
J. W. Brinkman, D. de Zeeuw, H. J. Lambers Heerspink, R. T. Gansevoort, I. P. Kema, P. E. de Jong, and S. J.L. Bakker Apparent Loss of Urinary Albumin during Long-term Frozen Storage: HPLC vs Immunonephelometry
Clin. Chem.,
August 1, 2007;
53(8):
1520 - 1526.
[Abstract][Full Text][PDF]
P. E. de Jong and G. C. Curhan Screening, Monitoring, and Treatment of Albuminuria: Public Health Perspectives
J. Am. Soc. Nephrol.,
August 1, 2006;
17(8):
2120 - 2126.
[Abstract][Full Text][PDF]
D. de Zeeuw, H.-H. Parving, and R. H. Henning Microalbuminuria as an Early Marker for Cardiovascular Disease
J. Am. Soc. Nephrol.,
August 1, 2006;
17(8):
2100 - 2105.
[Abstract][Full Text][PDF]