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Ji C, Sykes L, Paul C, Dary O, Legetic B, Campbell NRC, Cappuccio FP. Systematic review of studiescomparing 24-hour and spot urine collections for estimating population salt intake. Rev Panam SaludPublica. 2012;32(4):30715.

Suggested citation

Rev Panam Salud Publica 32(4), 2012 307

Systematic review of studies comparing24-hour and spot urine collections forestimating population salt intake

Chen Ji,1 Lindsay Sykes,2 Christina Paul,1 Omar Dary,3 Branka Legetic,4

Norm R. C. Campbell,2 and Francesco P. Cappuccio1 on behalf of the

Sub-Group for Research and Surveillance of the PAHOWHO

Regional Expert Group for Cardiovascular Disease Prevention

Through Population-wide Dietary Salt Reduction

Objective. To examine the usefulness of urine sodium (Na) excretion in spot or timed urine sam-ples to estimate population dietary Na intake relative to the gold standard of 24-hour (h) urinary Na.Methods. An electronic literature search was conducted of MEDLINE (from 1950) andEMBASE (from 1980) as well as the Cochrane Library using the terms sodium, salt, andurine. Full publications of studies that examined 30 or more healthy human subjects withboth urinary Na excretion in 24-h urine and one alternative method (spot, overnight, timed)were examined.Results. The review included 1 380 130 participants in 20 studies. The main statisticalmethod for comparing 24-h urine collections with alternative methods was the use of a cor-relation coefficient. Spot, timed, and overnight urine samples were subject to greater intra-individual and interindividual variability than 24-h urine collections. There was a wide rangeof correlation coefficients between 24-h urine Na and other methods. Some values were high,suggesting usefulness (up to r = 0.94), while some were low (down to r = 0.17), suggesting alack of usefulness. The best alternative to collecting 24-h urine (overnight, timed, or spot) wasnot clear, nor was the biological basis for the variability between 24-h and alternative methods.Conclusions. There is great interest in replacing 24-h urine Na with easier methods to as-sess dietary Na. However, whether alternative methods are reliable remains uncertain. Moreresearch, including the use of an appropriate study design and statistical testing, is requiredto determine the usefulness of alternative methods.

Sodium chloride, dietary; urine specimen collection; population.

abstract

Key words

In steady-state conditions, the kidneyshandle most of the sodium (Na) con-sumed in a day. The majority (up to 95%)is excreted in the urine within 24 hours(h). The remainder is excreted through

sweat, saliva, and gastrointestinal secre-tions. The daily renal excretion rate ofNa is not constant throughout the 24 h;it depends on Na consumption patterns,such as time of day, an individuals pos-ture, and neurohormonal influences.

A 24-h urine collection is the goldstandard for assessing salt intake

1 University of Warwick, World Health Organiza-tion Collaborating Centre for Nutrition, War-wick Medical School, Coventry, United Kingdom.Send correspondence to: Francesco P. Cappuccio,[email protected]

2 Libin Cardiovascular Institute of Alberta, Univer-sity of Calgary, Calgary, Alberta, Canada.

3 Academy for Educational Development, Washing-ton, D.C., United States of America.

4 Area of Health Surveillance and Disease Manage-ment, Pan American Health OrganizationWorld

Artculo de revisin / Review

Health Organization, Washington, D.C., UnitedStates of America.

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Rev Panam Salud Publica32(4), 2012

Review Ji et al. Comparing 24-hour and spot urine collections

through urinary Na excretion in indi-viduals and in populations (1). How-ever, it is often deemed inconvenientfor repeated use in large populationstudies. There are concerns that a highparticipation burden, a lack of com-pleteness, and a high cost will affect theresponse rate and the practicality of us-

ing the test. Alternative methods, suchas spot and timed urine samples, have

been derived in an attempt to overcomethis concern.

Assessing a populations salt intakeand its changes over time underpinssalt reduction policies and represents amajor pillar of such programs globally(25). Yet, for many countries salt intakeis not known.

Several questions need answering.Can average population salt intake beassessed with methods other than 24-hurine collections? Can daily intake be

predicted from spot urine samples? Candaily intake be estimated from spoturine samples? Is validation for groupsthe same as that for individuals? Canmethods other than 24-h urine Na beused for reliable monitoring of popula-tion changes? Are these methods validin different population subgroups ac-cording to gender, age, and ethnicity?

The aim of this study was to sys-tematically review all studies compar-ing 24-h urine collections with alterna-tive methods (spot, overnight, daily,timed) to assess salt intake in adults and

children.

METHODS

Literature search

A search strategy was developed toidentify studies that reported the asso-ciation between Na excretions obtainedwith 24-h urine collections comparedwith spot urine samples. The electronicdatabases MEDLINE (from 1950 toApril, week 4, 2010) and EMBASE (from1980 to May, week 1, 2010) as well as the

Cochrane Library were searched usingthe terms sodium [dietary, chloride,intake, excretion], salt [intake], andurine [timed, spot, random, 24-h]. Ref-erence lists of original and review ar-ticles were examined to search for morestudies. Only full-length articles wereconsidered. English language restrictionwas applied. Only studies on humanswere included.

Inclusion and exclusion criteria

Studies had to fulfil the following crite-ria: full paper, human study, populationstudy or those in large groups (n 30),availability of 24-h urine and urine col-lected by an alternative method (spot,overnight, timed), and availability of uri-

nary analytes. Studies were excluded if:not in English, in abstract form, samplesize < 30, and done in special patientgroups (e.g., renal or heart failure, con-gestive heart disease, diabetes, or patientgroups on medication). If multiple pub-lished reports from the same study wereavailable, only the one with the mostdetailed information for exposure andoutcome was included.

Data extraction

Three investigators (C.J., L.S., and

C.P.) extracted data independently anddifferences were resolved by discussionand consensus. Relevant data includedthe first authors surname, year of pub-lication, country of origin of populationstudied, population type, sample size,age of population, duration of study,description of urine sampling, meanNa for 24-h and for alternative samples,

and outcome measures (correlations,ratios).

RESULTS

Characteristics of studies

Forty-three papers met the inclusion

criteria. Of them 23 were excluded be-cause of lack of data and 20 were suitablefor final review: 16 in adults (621) and4 in children (2225) (Figure 1). Whenresults were reported separately for in-dependent groups, they were enteredinto the tabulation as separate studies(9, 13, 18, 19, 22). Overall, the reviewincluded 1 380 130 participants from 7countries (5 from the United States ofAmerica, 6 from Japan, 3 from China,2 from Brazil, and 1 each from France,Croatia, and the Netherlands). Fourteenstudies recruited both men and women;

2 studies recruited only women. Fourstudies in five samples were carried outon children and adolescents.

Studies comparing 24-h withovernight samples in adults

Table 1 summarizes studies in adults.Nine studies tested the correlation

Papers retrieved from EMBASEdatabase:

No. = 3 686

Papers retrieved from MEDLINEdatabase:

No. = 1 360

Papers including both24-hour and spot/timed urine

sodium:No.= 23

Papers including both24-hour and spot/timed urine

sodium:No.= 37

Total valid papers afterduplicate papers included:

No. = 43

Papers excluded afterbeing read:

No. = 23

Final systematic review:No. = 20

(No. = 4 children and adolescents)

FIGURE 1. Fowchart of systematic review

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310



Costaetal.

1994(15)

Brazil

Healthyindiv

iduals

611

2074

Singletest

24hversusspot

220

n/a

Yes

0.28

Flamephotometry.Spotu

rineoverestimatesNa

excretion.

Panetal.

1994(16)

China

Researchsta

ff

21men,19

women

24

1month

24hversus

half-day(hd)

versusov

151

69hd

31ov

No

0.83versus

sameday

0.41versus

adjacentday

0.41versus1

monthapart

usinghd

urine

0.60versus

sameday

0.28versus

adjacentday

0.28versus

1month

apartusing

ovurine

Ion-selectiveelectrodemethod.

Tanakaet

al.2002

(17)

Japan

Group1:

INTERSALT

participants,Group2:

manualworkers

295men,

296women

2059

n/a

24hversusspot

187

179(estimated)

Yes

0.54

Emissionflamephotometry.Estimatedmeans

lostaccuracyonlowersaltintakes.Spoturines

underestimatedtrueexcretion.Needspopulation-

specificvalidationwithag

e,weight,height,and24-h

sample.

Kamata

andTochikubo

2002(18)

Japan

Healthyindiv

iduals

Study1:126

men,225

women

3850

n/a

24hversus

predictedbyCr

andleanmass

n/a

n/a

No

0.73

0.78

AutomatedIEM.Populationspecific,needsvalidation.

Overnighturineunderestimatestruevaluewithgender

differencesandriskofbia

s.

Kamata

andTochikubo

2002(18)

Japan

Healthyindiv

iduals

Study2:

71men,

78women

3549

n/a

24hversusov

withsampling

pipe

n/a

n/a

No

0.59

0.67

AutomatedIEM.Population-specific,needsvalidation.

Overnighturineunderestimatestruevaluewithgender

differencesandriskofbia

s.

Yamasue

etal.2006

(19)

Japan

Healthyadults

Study1:62

men,188

women

54

n/a

24hversusov

n/a

n/a

No

n/a

Comparingtwomethods

Yamasueet

al.2006(19)

Japan

Healthyadults

Study2:

70men,

154women

53

2166days

24hwithIEM

versusovwithNSM

n/a

n/a

No

0.72

Comparingtwomethods

Ilichetal.

2009(20)

Croatia

Healthypartic

ipants

143women

3079

n/a

24hversusfasting

spot

16.6

b

12.9

b

Yes

0.452

Flameatomicabsorption/e

missionspectrometry.

Mannand

Gerber

2010(21)

United

Statesof

America

Unselectedvolunteers

81

2182

n/a

24hversusspot,

AM,andPM

181spot

188AM

164PM

160

176

158

No

0.17spot

0.31AM

0.86PM

Treatedindividuals.

Notes:Ind.:independent,Na:sodium,Cr:creatinine,n/a:notavailable,IEM:ion-electrodemethod,

NSM:new

saltmonitor,h:hour,d:daytime,ov:overnight,n:nighttime.

a

Na(mmol/h).

b

Na/Crratio(mmol/h).

TAblE1.

(Continued)

Author,

year(ref.)

Country

Population

Sample

size

Age,

years

Duration

Urinesamples

MeanNaamount,mmol

Ind.

samples

Correlation

N

otes

24h

Spot

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Ji et al. Comparing 24-hour and spot urine collections Review

between 24-h and overnight urinary Na(68, 11, 12, 14, 16, 18, 19). Ten studiesused flame photometry to analyze Naconcentrations (6, 7, 915, 17), one (16)used an ion-selective electrode method,and one (19) used a new salt monitor.One study analyzed the correlation coef-ficient of the true mean 24-h urine Na

and the true mean overnight urine Na inorder to eliminate the influence of intra-individual variation (6). It suggestedthat at least a week of overnight sampleswould be required to reduce the intra-individual variation.

Luft et al. studied the Na intake byplacing participants on a fixed diet andmonitoring their urinary output (8).They found that the mean Na intakeshowed a greater correlation with the24-h (r = 0.75) than with the overnight(r = 0.55) Na. They recognized that dailyvariation in salt intake is a limitation

and concluded that overnight urine col-lections do not appear to be a promisingway to estimate mean Na intake.

Another study found a correlation of0.94 between the true mean 24-h andovernight Na excretion (11). The urinesamples were not collected on consecu-tive days. Another study collected six24-h urine samples gathered over 10days and reported a high correlation

between the true mean overnight and24-h urine Na (r = 0.92) (12). There wasa greater degree of intra- and interin-dividual variation with the overnight

urine Na collections than with the 24-hexcretions and thus a greater number ofsamples would be needed to accuratelymeasure Na intake in populations.

He et al. found a correlation coefficientof 0.843 between the 24-h and overnighttrue mean values when pooling datafrom rural and urban residents (14).Despite a strong correlation, double theamount of samples would be needed tolimit the diminution of correlation coef-ficient to < 5%. The strength of this studywas the inclusion of rural populationsamples in contrast to previous stud-

ies of predominantly urban populationswith a high salt intake.

In relation to time of day, one studyfound that the correlations between 24-hurinary electrolytes and half-day (12-hduration) urine contents were betterthan correlations with overnight (8-hduration) samples (16). This finding wasprobably due to the longer time periodinvolved with the half-day collections.This study did not find a strong corre-

lation between the 24-h and overnighturine Na and cautioned about using apartial sample as a substitute for 24-hurinary Na analysis.

A few studies piloted the use of pur-pose-built devices to facilitate partialurine collections. Kamata and Tochikubodevised a urine-sampling pipe with a

two-way stopcock that could trap over-night urine proportionally to estimatethe volume of overnight urine and toestimate 24-h urine Na (18). They ac-counted for the lean body mass of indi-viduals to estimate the 24-h urine Na lev-els. Using an electrical device to monitordaily salt intake at home, another studyfound a significant correlation between24-h urine Na excretion and overnightvalues (19). The correlation between 24-hurine Na with an ion-electrode methodand the measured value with a new saltmonitor using overnight urine was sig-

nificant (r = 0.72). The self-monitoringmethod suggested overnight samplingas an adequate substitute for 24-h urinecollection.

Studies comparing 24-h with spotsampling in adults

Eight studies included in the reviewcompared 24-h urine Na contents andsingle spot urine Na (7, 9, 10, 13, 15, 17,20, 21).

Kawasaki et al. showed that in 242participants a single 24-h urine specimen

did not represent the individual averageof daily Na excretions (9). The correla-tion coefficient between spot and 24-hurine was 0.467. When they averaged 3daily collections from 117 participants,the correlation coefficient was 0.624.They also compared urine samples from59 persons with an intra-individual stan-dard deviation of a spot urine specimenfor excretion of creatinine within 20%.The correlation coefficient was 0.725.

Wolf et al. looked at using a spot urinesample instead of the usual 24-h sampleto measure urine Na (10). There was an

overestimation of both the excretion rateand the Na/creatinine ratio when thespot urine was compared with the 24-hsample. The spot sample, carried out inthe morning after overnight fasting, wasclosely related to the 24-h sample.

Kawasaki et al. found that spot sam-ples of second morning voided urine,collected over 3 days, give a more reli-able and accurate estimation of 24-hurine Na than a 1-day collection (13).

They found a highly significant correla-tion (r = 0.774). They also found that thecorrelation was stronger when they usedmorning spot samples rather than nightsamples.

Costa et al. analyzed the relationshipbetween systolic pressure and Na ex-cretion at different levels of diastolic

pressure (15). They used a single cas-ual spot sample instead of 24-h urineto estimate Na excretion. They foundthat spot samples showed significantlyhigher estimates of Na excretion than24-h collections, with a weak positivecorrelation coefficient (r = 0.28). Theyconcluded that this weak but significantcorrelation suggests that an even largersample of spot urine collections would

be needed compared with 24-h urinesamples to detect an association between

blood pressure and Na excretion.Tanaka et al. found that the correla-

tion between the 24-h and the spot urineNa was 0.65 (17). They concluded thatthe method would be a convenient andaccurate way to estimate population Naintake. They discussed that individualmonitoring should still use 24-h sam-ples, but spot samples are good alterna-tives to monitor and evaluate populationmean Na intake.

In another study, the ratio between24-h and spot samples was 2.0 (20).The study also reported a correlation

between spot and 24-h urine Na of 0.45.This study concluded that spot urine

could be used instead of tedious andimpractical 24-h urine collection. Thestudy noted that spot sampling is notsufficient in all cases but is a reliablealternative to 24-h sampling.

More recently, Mann and Gerber com-pared three spot samplesrandom, AM,and PMwith a 24-h sample (21). WhenNacreatinine ratios were adjusted for24-h creatinine excretion, all correlationswere strengthened. The correlations be-tween the 24-h Na excretions were 0.17,0.31, and 0.86 for random, AM, and PMsamples, respectively. The value for the

random sample was not significantlycorrelated and therefore would not be agood alternative to 24-h urine Na collec-tions. However, a spot sample collectedin the late afternoon or early evening be-fore dinner, adjusted for 24-h creatinineexcretion, accurately predicts 24-h Naexcretion. They concluded that the use ofspot urine is convenient and cost-effec-tive in assessing Na excretion in clinicalpractice and epidemiologic studies.

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All but one study comparing spot and24-h urine collections advocated usingthe spot sampling method (9). There wasa significant consensus that using spoturine samples would require a greaternumber of collections, but it would still

be more convenient and feasible for gen-eral populations that require monitoring.

Studies comparing 24-h with multipleother sampling techniques in adults

Yamori et al. looked at 24-h urine sam-ples split in three parts and found thatthe highest correlation of Na in the urinesamples occurred in the daytime voidedurine and the second highest correla-tion was in the overnight voided urine(7). The correlation was low. Despitethe higher correlation between daytimevoided urine and 24-h collection, practi-cality favors evening and overnight col-

lections as most individuals can do themat home. They suggest the use of partialurine samples to analyze Na intake and

even the use of single spot urine samplesfor large population surveys.

Studies comparing 24-h with othersampling techniques in children

The studies in children and adoles-cents are summarized in Table 2. The

studies included ages 318 years andcompared overnight urine samples with24-h samples. In all studies, multiple col-lections were used [from a minimum of2 (23) to a maximum of 7 (22, 25) days].Most studies used correlation coeffi-cients to assess concordance, reliability,and reproducibility, with values varyingfrom 0.62 (24) to 0.95 (25).

DISCUSSION

This study is the first systematic re-view of studies comparing simple mea-

sures of urine Na excretion with 24-hurine Na excretion. The studies areheterogeneous in objectives, protocols,

types of urine collections, number ofrepeated measures, populations studied,measures taken for validation, and ana-lytic approaches. This study does not,therefore, provide a uniform pool of datato assess the evidence with consistency,as reflected in the contrasting conclu-sions that have been reached over the

years in favor of and against the suitabil-ity of alternative methods for assessingurine Na excretion (a proxy for salt in-take) instead of 24-h urine Na excretion.

Advantages and disadvantages

There are advantages and disadvan-tages in the different options (1, 2). Thegold standard for assessing daily saltintake is 24-h urine collection. It cap-tures > 90% of the Na ingested aroundthe time of collection. When applied topopulation samples, however, it may

pose a high burden on participants,with a resultant risk of low participa-tion rates.

TAblE 2. Systematic review of studies in chidren and adoescents

Author, year(ref.) Country Population

Samplesize

Age(years)

UrineSamples Duration

Mean Na amount,mmol

Independentsample Correlation Notes24 h Spot

Liu et al.1979 (6)

UnitedStates ofAmerica

Grades 68 31 boys 1114 24 h versusovernight

7 days 123 49 No 0.73 Automated methods.Conditional probabilityof 24 h in 5th quintile to3rd tertile ranges from

0.59 to 0.78, givennighttime Na in 5thquintile.

Liu et al.1979 (22)

UnitedStates ofAmerica

Grades 68 42 gir ls 1114 24 h versusovernight

7 days 150 69 No 0.73 Automated methods.Conditional probabilityof 24 h in 5th quintile to3rd tertile ranges from0.59 to 0.78, givennighttime Na in 5thquintile.

Micheli andRosa2003 (23)

Brazil Childrenand teens

31 617 24 h versusovernightversus foodrecord

2 days 146, 162 137 No 0.71 Ion selective electrodemethod. 24-h urine stillmost reliable way todetermine urine Na.

Luft et al.1984 (24)

UnitedStates of

America

Twins 52 boys,43 girls

318 24 h versusovernight

5 daysover 1

month

115 37(night)

No 0.62 Flame photometry.

Knuimanet al.1988 (25)

Netherlands Boys 28 89 24 h versusovernight

7 days 101 34(night)

No 0.95 Flame atomicabsorptionspectrometry.Overnight may replace24 h in young boys, butmore overnight than24-h specimens arerequired to achievesimilar precision.

Note:Na: sodium.

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The inaccuracy of completeness (bothunder- and overcollections) is also aconcern. The biochemical method of ad-ministering para-aminobenzoic acid for3 days before urine collection wouldovercome this problem (2628). The

body does not metabolize para-amino-benzoic acid and, once absorbed in the

bloodstream, it is flushed through thekidneys with excretion being ~ 100%of the ingested load. A direct measure-ment of para-aminobenzoic acid in theurine would allow a direct measureof completeness. However, this methoddoes not provide a feasible alternativefor population monitoring, especiallyin low- and middle-income countries.It reduces the response rate, as partici-pants have to plan in advance and takethree pills on the days before collection.Nonresponders (hence defaulters) will

be identified only after para-aminoben-

zoic acid has been measured (and un-detected) in the urine, with resourceimplications in terms of additional labo-ratory costs, pill costs, and unnecessaryscreenings.

A less precise but more feasible al-ternative is to measure urine creatinineexcretion, which is constant within anindividual at rest and depends mainlyon lean body mass and age.

One advantage of 24-h urine collec-tion is that it can be used at the sametime for monitoring total iodine intakeand therefore complements population

programs of universal salt iodization forthe prevention of iodine deficiency (29).

Feasibility and usefulness

For more than four decades, 24-h urinecollections have been used in populationstudies. The most compelling evidenceof feasibility and usefulness comes fromthe INTERSALT study, an internationalstudy of the relationships between saltintake and blood pressure (30). INTER-SALT was carried out in 52 populationsamples on all continents and included

samples from remote populations inthe Amazon jungle, Africa, Australasia,and rural China. Practicalities were ad-dressed with local training that allowedthe quality of 24-h urine collections to bepreserved.

In addition, community-based studiesin rural Africa have been able to perform24-h urine collections with training ofhealth care assistants at low cost (3134).

Alternative methods

Several methods of partial urine col-lections (spot, timed, daytime, evening,overnight) are alternatives to 24-h urinecollection. They are less onerous forparticipants, can allow faster screeningtime, and require less training for staff.

They are highly variable at the indi-vidual level but can give reasonable es-timates of group means, an aspect thatmakes them of interest for long-termmonitoring and population surveillance.These methods are highly dependent onhydration, duration and volume of col-lection, and high proportional residual

bladder volume. They are expressed asNa concentration per liter (rather thantotal daily excretion) and are convertedto estimated 24-h Na excretion. Nomeans is available to establish the pre-cision, validity, and reliability of these

conversions.The method of Tanaka et al. (17), for

example, is population specific; requiresinternal calibration with age, weight,and creatinine; overestimates low in-takes and underestimates high intakes;and has very low specificity for identify-ing lower salt intake (35). Moreover, therelationship between urine concentra-tions and total excretions does not giveinformation on population distributions(36).

Spot urine samples are currently usedto monitor iodine status in global salt

iodization programs around the world,mainly in children and in women ofchildbearing age (29). These methodsare less desirable for the initiation ofmonitoring programs of population saltreduction because they cannot providean absolute measure of salt intake at

baseline. However, they may prove use-ful in repeated assessments over thecourse of the programs to assess relativechanges from a known baseline (1).

Implications for future research andpolicy

The assessment of population salt in-take underpins the implementation ofpolicies to reduce salt intake (2, 5). Thisresult can be achieved by measuringand estimating average population lev-els and average changes over time in thepopulation as a whole and in subgroupsas well as in population distributions(36). This objective differs from the need

to measure an individuals salt intake.This systematic review indicates thatmost studies aimed at answering thelatter question, and almost every studyrelied on correlation analyses and thestrength of the correlation coefficientsto draw conclusions. Most studies com-pared 24-h urine data with data derived

from partial collections that were part ofthe 24-h collection (i.e., dependent col-lections) rather than independent of it.This important point was recently high-lighted by Mann and Gerber (21). Theappropriate validation test would be be-tween a 24-h sample and an alternativesample independent of the 24-h collec-tion to avoid spurious intercorrelations(as it would be when reassessing saltintake in different population samplesover time).

Correlation may not be the best mea-sure to assess the question in the current

context of monitoring and evaluatingpublic health programs of populationsalt reduction in which average valuesare estimated and followed up overtime. Very few studies have used thisapproach. In Scotland, for example,in the 2006 Health Survey 24-h urineNa was weakly correlated with a urineNa/creatinine ratio obtained from spoturine collections (37). There was poorreproducibility of three consecutive spoturines (worse in women) and poor dis-crimination among groups in the second,third, and fourth quintiles of 24-h urine

Na distribution.A recent study reported the results of

a comprehensive validation analysis of24-h compared with timed and indepen-dent urine collections in a British mul-tiethnic population of men and womenand independently validated in anotherpopulation sample of Italian men (35).The study compared different methodsto estimate 24-h Na output from timedcollections and used not only correla-tions but BlandAltman plots, predictionof quintile position, and sensitivity andspecificity of detecting a reduction of Na

excretion below 100 mmol/day using re-ceiver operating characteristic areas un-der the curve. The study shows consis-tent bias, moderate sensitivity, and lowspecificity using timed urine samples.

Finally, a national survey of salt intakein Ireland used spot urine collectionsto estimate population levels of salt in-take and 24-h collections in an indepen-dent subsample of the population (38).

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17. Tanaka T, Okamura T, Miura K, KadowakiT, Ueshima H, Nakagawa H, et al. A simplemethod to estimate populational 24-h uri-

nary sodium and potassium excretion usinga casual urine specimen. J Hum Hypertens.2002;16:97103.

18. Kamata K, Tochikubo O. Estimation of 24-hurinary sodium excretion using lean body

mass and overnight urine collected by apipe-sampling method. J Hypertens. 2002;20:21917.

19. Yamasue K, Tochikubo O, Kono E, MaedaH. Self-monitoring of home blood pressurewith estimation of daily salt intake usinga new electrical device. J Hum Hypertens.2006;20:5938.

20. Ilich JZ, Blanusa M, Orlic ZC, Orct T, Kos-tial K. Comparison of calcium, magnesium,sodium, potassium, zinc, and creatinine con-centration in 24-h and spot urine samples inwomen. Clin Chem Lab Med. 2009;47:21621.

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25. Knuiman JT, van Poppel G, Burema J, van derHeijden L, Hautvast JGAJ. Multiple overnight

REFERENCES

The average values were close to eachother (10.3 versus 10.4 g of salt/day inmen and 7.4 versus 7.4 g of salt/day inwomen). The study did not break downdata by age or by quintile of salt intaketo determine whether biases across agesand levels of intake were present.

Conclusion

Although inconclusive in providing ananswer to modify current recommenda-tions, this systematic review highlightsthe inadequacies of current evidence andthe need for validation studies pertinentto the context of population monitor-ing of salt intake and of evaluation andsurveillance of salt reduction programs.It suggests that 24-h urine collections insmall surveys are viable and reliable. Inthe absence of more definitive evidence,the authors endorse the recommenda-

tions of the Pan American Health Or-ganizationWorld Health OrganizationRegional Expert Group in that untilmore studies are carried out to assess

simpler but reliable methods of urinecollection for the purpose of estimatingdaily excretions [of sodium], 24 hoururine collections are recommended (1).

Disclosure. This publication does notnecessarily represent the decisions orthe stated policy of the World Health

Organization (WHO); the designationsused and the presentation of material donot imply the expression of any opinionon the part of WHO. F.P.C. is an unpaidmember of Consensus Action on Saltand Health, an unpaid member of WorldAction on Salt and Health (WASH), anunpaid technical advisor to WHO andthe Pan American Health Organization(PAHO), an individual member of theNational Heart Forum, and a member ofthe executive committee and a trustee ofthe British Hypertension Society. N.C.is an unpaid member of WASH and

many other governmental and nongov-ernmental committees related to dietarysodium and to hypertension preven-tion and control and has salary support

from the Heart and Stroke Foundation,Canadian Institute for Health ResearchChair in Hypertension Prevention andControl. F.P.C., O.D., B.L., and N.C.were members of the PAHOWHO Re-gional Expert Group for CardiovascularDisease Prevention through population-wide dietary salt reduction.

Acknowledgments.The authors thankBarbara Legowski, Ricardo Correa-Rotter, and all members of the PAHOWHO Expert Group for support andfeedback. F.P.C. chaired the Sub-Groupfor Research and Surveillance of thePAHOWHO Expert Group, designedthe electronic search, supervised re-searchers, and drafted the manuscript.N.C. supervised researchers. C.J., L.S.,and C.P. ran the electronic searches,retrieved and reviewed papers, anddrafted tables of results. All authors con-

tributed to the discussions and made sig-nificant contributions to the draft manu-script. C.J. and L.S. contributed equallyto this work. F.P.C. acts as guarantor.

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Objetivo. Analizar la utilidad de la medicin de la excrecin urinaria de sodio apartir de la recoleccin puntual o cronometrada de muestras de orina para calcular laingesta de sodio alimentario en la poblacin, en relacin con la prueba de referenciaque mide la excrecin de sodio en orina de 24 horas.Mtodos. Se realiz una bsqueda de bibliografa electrnica en MEDLINE (desde1950) y EMBASE (desde 1980), as como en la Biblioteca Cochrane, empleando lostrminos sodium, salt y urine (sodio, sal y orina). Se examinaron las publicacionescompletas de los estudios que incluan 30 o ms sujetos humanos sanos en los que sehubiera determinado la excrecin de sodio mediante la recoleccin de orina de 24 horaso un mtodo alternativo (recoleccin puntual, de toda la noche, cronometrada).Resultados. La revisin incluy a 1 380 130 participantes de 20 estudios. El principalmtodo estadstico adoptado para comparar las recolecciones de orina de 24 horascon los mtodos alternativos fue el uso de un coeficiente de correlacin (r). Lasmuestras de orina recolectadas de forma puntual, cronometrada y de toda la nocheestaban sujetas a mayor variabilidad intra e interindividual que las recolecciones de

orina de 24 horas. Se obtuvo una amplia gama de coeficientes de correlacin entre lasdeterminaciones de sodio en orina de 24 horas y mediante los otros mtodos. Algunosvalores fueron elevados, lo que indica su utilidad (r de hasta 0,94), mientras queotros fueron bajos (r por debajo de 0,17), lo que indica su falta de utilidad. La mejoralternativa a la obtencin de orina de 24 horas (de toda la noche, cronometrada, opuntual) no result evidente, ni tampoco la base biolgica de la variabilidad entre elmtodo de 24 horas y los alternativos.Conclusiones. Hay mucho inters en remplazar la determinacin de sodio en orinade 24 horas por otros mtodos ms fciles de evaluacin del sodio alimentario.Sin embargo, sigue habiendo incertidumbre sobre la fiabilidad de los mtodosalternativos. Es preciso ampliar la investigacin, incluido el uso de un diseo deestudio y pruebas estadsticas apropiados, para determinar la utilidad de los mtodosalternativos.

Cloruro de sodio diettico; toma de muestras de orina; poblacin.

resumen

Revisin sistemtica deestudios comparativos entrerecoleccin de muestras deorina de 24 horas y puntual

para calcular el consumo desal en la poblacin

Palabras clave

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hour urinary sodium and potassium excre-tion. Br Med J. 1988;297:31928.

31. Adeyemo AA, Prewitt TE, Luke A, OmotadeOO, Rotimi CN, Brieger WR, et al. The fea-sibility of implementing a dietary sodiumreduction intervention among free-living nor-motensive individuals in south west Nigeria.Ethn Dis. 2002;12:20712.

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Manuscript received on 27 June 2012. Revised versionaccepted for publication on 5 October 2012.

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