European Journal of Clinical Nutrit

European Journal of Clinical Nutrition (2003) 57, Suppl 2, S6–S9
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ORIGINAL COMM UNICATION

Markers of hydration status

SM Shirreffs1*

1School of Sport and Exercise Sciences, Loughborough University, Leicestershire, UK


Many indices have been investigated to establish their potential as markers of hydration status. Body mass changes, blood indices, urine indices and bioelectrical impedance analysis have been the most widely investigated. The current evidence and opinion tend to favour urine indices, and in particular urine osmolality, as the most promising marker available.
European Journal of Clinical Nutrition (2003) 57, Suppl 2, S6 – S9. doi:10.1038/sj.ejcn.1601895

Keywords: hydration status; water balance; euhydration; hypohydration




Hydration status—some definitions
Euhydration is the state or situation of being in water balance. However, although the dictionary definition is an easy one, establishing the physiological definition is not so simple. Hyperhydration is a state of being in positive water balance (a water excess) and hypohydration the state of being in negative water balance (a water deficit). Dehydration is the process of losing water from the body and rehydration the process of gaining body water. Euhydration, however, is not a steady state, but rather is a dynamic state in that we continually lose water from the body and there may be a time delay before replacing it or we may take in a slight excess and then lose this (Greenleaf, 1992).


Water intake and loss
The routes of water loss from the body are the urinary system via the kidney, the respiratory system via the lungs and respiratory tract, via the skin, even when not visibly sweating, and the gastrointestinal system as faeces or vomit. The routes of water gain into the body are gastrointestinally from food and drink consumption and due to metabolic production. Many textbooks, both recent and older, state water gain and loss figures for the average sedentary adult in a moderate environment in the order of 2550 ml (McArdle et al, 1996), 2600 ml (Astrand & Rodahl, 1986) and 2500 ml (Diem, 1962). However, it is interesting to note that the source of this data is never given.


*Correspondence: SM Shirreffs, School of Sport and Exercise Sciences, Loughborough University, Leicestershire LE11 3TU, UK.
E-mail: [e-mail]
Guarantor: SM Shirreffs.
Measurement of total body water
The body water content of an individual can be measured or estimated in a number of ways, but the current consensus is that tracer methodology gives the best measure of total body water. Deuterium oxide (D2O or 2H2O) is the most commonly used tracer for this purpose and full details of the methods and protocols, assumptions and limitations are well discussed elsewhere (Schoeller, 1996). Briefly, the tracers are distributed relatively rapidly in the body (in the order of
3–4 h for an oral dose) and correction can be made for exchange with nonaqueous hydrogen. It is estimated that total body water can be measured with a precision and accuracy of 1–2%.



Assessing hydration status
Hydration status has been attempted to be assessed in a variety of situations for a number of years. In 1975, Grant and Kubo divided the tests open to use in a clinical setting into three categories: laboratory tests, objective noninvasive measurements and subjective observations. The laboratory tests were measures of serum osmolality and sodium concentration, blood urea nitrogen, haematocrit and urine osmolality. The objective, noninvasive measurements in- cluded body mass, intake and output measurements, stool number and consistency and ‘vital signs’, for example, temperature, heart rate and respiratory rate. The subjective observations were skin turgor, thirst and mucous membrane moisture. This manuscript concluded that, although the subjective measurements were least reliable, in terms of consistency of measurement between measurers, they were the simplest, fastest and most economical. The laboratory tests were deemed to be the most accurate means to assess a




patient’s hydration status. Since this manuscript was pub- lished, there has been a large amount of research into some of these measurements, observations and tests, and some of the main ones, along with others, are discussed in the rest of this paper.


Body mass
Acute changes in body mass over a short time period can frequently be assumed to be due to body water loss or gain; 1 ml of water has a mass of 1 g (Lentner, 1981) and therefore changes in body mass can be used to quantify water gain or loss. Over a short time period, no other body component will be lost at such a rate, making this assumption possible.
Throughout the exercise literature, changes in body mass over a period of exercise have been used as the main method of quantifying body water losses or gains due to sweating and drinking. Indeed, this method is frequently used as the method to which other methods are compared. Respiratory water loss and water exchange due to substrate oxidation are sometimes calculated and used to correct the sweat loss values, but this is not always done (Mitchell et al, 1972). Examples of such types of calculations are shown in Table 1.


Blood indices
Collection of a blood sample for subsequent analysis has been both investigated and used as a hydration status marker. Measurement of haemoglobin concentration and haemato- crit has the potential to be used as a marker of hydration status or change in hydration status, provided a reliable baseline can be established. In this regard, standardisation of posture for a time prior to blood collection is necessary to distinguish between postural changes in blood volume, and therefore in haemoglobin concentration and haematocrit, which occur
(Harrison, 1985) and change due to water loss or gain. Plasma or serum sodium concentration and osmolality
will increase when the water loss inducing dehydration is hypotonic with respect to plasma. An increase in these concentrations would be expected, therefore, in many cases of hypohydration, including water loss by sweat
Markers of hydration status
SM Shirreffs
S7
secretion, urine production or diarrhoea. However, in subjects studied by Francesconi et al (1987), who lost more than 3% of their body mass mainly through sweating, no change in haematocrit or serum osmolality was found, although as described below certain urine parameters did show changes. Similar findings to this were reported by Armstrong et al (1994, 1998). This perhaps suggests that plasma volume is defended in an attempt to maintain cardiovascular stability, and so plasma variables will not be affected by hypohydration until a certain degree of body water loss has occurred.
Plasma testosterone, adrenaline and cortisol concentra- tions were reported by Hoffman et al (1994) not to be influenced by hypohydration to the extent of a body mass loss of up to 5.1% induced by exercise in the heat. In contrast, however, plasma noradrenaline concentration did respond to the hydration changes, which means that it may be possible to use this as a marker of hydration status, at least when induced by exercise in the heat.


Urine indices
Collection of a urine sample for subsequent analysis has also been investigated and used as a hydration status marker.
Measurement of urine osmolality has recently been an extensively studied parameter as a possible hydration status marker. In studies of fluid restriction, urine osmolality has increased to values greater than 900 mosm/kg for the first urine of the day passed in individuals dehydrated by 1.9% of their body mass, as determined by body mass changes (Shirreffs & Maughan, 1998). Armstrong et al (1994) have determined that measures of urine osmolality can be used interchangeably with urine-specific gravity, opening this as another potential marker.
Urine colour is determined by the amount of urochrome present in it (Diem, 1962). When large volumes of urine are excreted, the urine is dilute and the solutes are excreted in a large volume. This generally gives the urine a very pale colour. When small volumes of urine are excreted, the urine is concentrated and the solutes are excreted in a small volume. This generally gives the urine a dark colour. Armstrong et al (1998) have investigated the relationship


Table 1 Examples of hydration status calculations



Exercise
Pre-exercise Body massa (kg)
Post-exercise Body massa (kg)
Total body mass loss or gaind
(ml or g)
Drinks consumed during exerciseb (ml)
Urine excreted during exercisec (ml)

Sweat volume
(ml)

Hydration statusd
(%)

60 min Running 70.00 68.00 2000 0 200 1800 2.9
3 h Walking 70.00 70.00 0 500 400 100 0.0
2 h Cycling 70.0 0 70.20 þ 200 1000 0 800 þ 0.3

aBody mass measured nude with dry skin.
bDrinks consumed any time between the two bod

Hasil (Bahasa Indonesia) 1:

European Journal of Clinical Nutrition (2003) 57, d 2, S6 – S9& 2003 alam Publishing Group semua hak dilindungi 0954-3007/03 $25,00www.Nature.com/ejcnASLI COMM UNICATION Penanda status hidrasiSM Shirreffs1 *1School olahraga dan latihan Sciences, Universitas Loughborough, Leicestershire, InggrisBanyak indeks telah menyelidiki membangun potensi mereka sebagai penanda status hidrasi. Perubahan massa tubuh, darah indeks, urin indeks dan Analisis Impedansi bioelectrical telah paling banyak diinvestigasi. Bukti saat ini dan pendapat cenderung mendukung indeks urin, dan di osmolalitas urin tertentu, sebagai yang paling menjanjikan penanda tersedia.European Journal of Clinical Nutrition (2003) 57, d 2, S6 – S9. Doi:10.1038/SJ.ejcn.1601895Kata kunci: status hidrasi; keseimbangan air; euhydration; hypohydrationStatus hidrasi — beberapa definisiEuhydration adalah negara atau situasi berada dalam keseimbangan air. Namun, meskipun definisi kamus mudah, membangun fisiologis definisi tersebut tidak begitu sederhana. Hyperhydration adalah sebuah negara berada dalam keseimbangan air positif (air kelebihan) dan hypohydration negara berada dalam keseimbangan air negatif (defisit air). Dehidrasi adalah proses kehilangan air dari tubuh dan rehidrasi proses mendapatkan tubuh air. Euhydration, namun, tidak kesetimbangan, tetapi adalah sebuah negara yang dinamis dalam bahwa kita terus-menerus kehilangan air dari tubuh dan mungkin ada penundaan waktu sebelum mengganti atau kita dapat mengambil sedikit kelebihan dan kemudian kehilangan ini (Greenleaf, 1992).Asupan air dan kerugianRute hilangnya air dari tubuh adalah sistem saluran kemih melalui ginjal, sistem pernapasan melalui paru-paru dan saluran pernafasan, melalui kulit, bahkan ketika tidak tampak berkeringat, dan sistem pencernaan sebagai kotoran atau muntah. Rute dari asupan air ke dalam tubuh yang gastrointestinally dari konsumsi makanan dan minuman dan karena produksi metabolik. Banyak buku, kedua negara baru dan lebih tua, air memperoleh dan kehilangan angka rata-rata orang dewasa menetap di lingkungan yang moderat dalam 2550 ml (McArdle et al, 1996), 2600 ml (Astrand & Rodahl, 1986) dan 2500 ml (Diem, 1962). Namun, hal ini menarik untuk dicatat bahwa sumber data ini tidak pernah diberikan.* Korespondensi: SM Shirreffs, sekolah olahraga dan latihan Sciences, Universitas Loughborough, Leicestershire LE11 3TU, UK.E-mail: [e-mail]: SM Shirreffs.Pengukuran air tubuh totalKadar air tubuh seorang individu dapat diukur atau diperkirakan dalam beberapa cara, tetapi saat ini konsensus adalah bahwa metodologi tracer memberikan ukuran terbaik dari tubuh total air. Oksida deuterium (D2O atau 2H2O) adalah perunut paling sering digunakan untuk tujuan dan rincian lengkap tentang metode dan protokol, asumsi dan keterbatasan ini adalah baik dibahas di tempat lain (Schoeller, 1996). Secara singkat, tracers didistribusikan relatif cepat dalam tubuh (dalam the rangka3-4 jam untuk dosis oral) dan koreksi dapat dibuat untuk pertukaran dengan nonaqueous hidrogen. Diperkirakan bahwa air tubuh total dapat diukur dengan presisi dan akurasi 1 – 2%.Menilai status hidrasiStatus hidrasi telah berusaha untuk dinilai dalam berbagai situasi untuk beberapa tahun. Pada tahun 1975, hibah dan Kubo dibagi tes terbuka untuk digunakan dalam pengaturan klinis ke dalam tiga kategori: tes laboratorium, tujuan pengukuran non-invasif dan pengamatan subjektif. Tes laboratorium adalah langkah-langkah konsentrasi osmolalitas dan natrium serum darah urea nitrogen, pendekatan haematocrit dan urin. Objektif, non-invasif pengukuran di menyimpulkan massa tubuh, pengukuran asupan dan output, feses nomor dan konsistensi dan 'vital signs', misalnya, suhu, denyut jantung dan laju pernafasan. Pengamatan subjektif yang kelembaban kulit turgor, Haus dan selaput lendir. Naskah ini menyimpulkan bahwa, meskipun subjektif pengukuran paling dapat diandalkan, dalam hal konsistensi pengukuran antara measurers, mereka adalah yang paling sederhana, tercepat dan paling ekonomis. Tes laboratorium dianggap menjadi yang paling akurat berarti untuk menilaistatus hidrasi pasien. Karena naskah ini adalah pub-lished, telah ada sejumlah besar penelitian beberapa pengukuran, pengamatan dan tes, dan beberapa yang utama, bersama dengan orang lain, yang dibahas di seluruh karya ini.Massa tubuhAkut perubahan dalam massa tubuh selama jangka waktu yang singkat dapat sering diasumsikan karena kehilangan air tubuh atau keuntungan; 1 ml air memiliki massa 1 g (Lentner, 1981) dan oleh karena itu perubahan dalam tubuh massa dapat digunakan untuk mengukur air keuntungan atau kerugian. Selama periode waktu yang singkat, ada bagian tubuh lainnya akan hilang pada tingkat seperti itu, membuat asumsi ini mungkin.Seluruh latihan literatur, perubahan dalam massa tubuh selama latihan telah digunakan sebagai metode utama kuantifikasi tubuh air kerugian atau keuntungan karena berkeringat dan minum. Memang, metode ini sering digunakan sebagai metode yang dibandingkan metode lain. Kehilangan air pernapasan dan air asing karena oksidasi substrat kadang-kadang dihitung dan digunakan untuk memperbaiki nilai-nilai kerugian keringat, tapi ini tidak selalu dilakukan (Mitchell et al, 1972). Contoh perhitungan jenis seperti ditunjukkan dalam tabel 1.Darah indeksKoleksi sampel darah untuk analisis selanjutnya telah baik diselidiki dan digunakan sebagai penanda status hidrasi. Pengukuran hemoglobin konsentrasi dan haemato-crit memiliki potensi untuk digunakan sebagai penanda status hidrasi atau perubahan status hidrasi, asalkan dapat diandalkan baseline dapat didirikan. Dalam hal ini, Standardisasi postur waktu sebelum pengumpulan darah diperlukan untuk membedakan antara perubahan postur dalam volume darah, dan oleh karena itu dalam konsentrasi hemoglobin dan haematocrit, yang terjadi(Harrison, 1985) and change due to water loss or gain. Plasma or serum sodium concentration and osmolalitywill increase when the water loss inducing dehydration is hypotonic with respect to plasma. An increase in these concentrations would be expected, therefore, in many cases of hypohydration, including water loss by sweatMarkers of hydration statusSM ShirreffsS7secretion, urine production or diarrhoea. However, in subjects studied by Francesconi et al (1987), who lost more than 3% of their body mass mainly through sweating, no change in haematocrit or serum osmolality was found, although as described below certain urine parameters did show changes. Similar findings to this were reported by Armstrong et al (1994, 1998). This perhaps suggests that plasma volume is defended in an attempt to maintain cardiovascular stability, and so plasma variables will not be affected by hypohydration until a certain degree of body water loss has occurred.Plasma testosterone, adrenaline and cortisol concentra- tions were reported by Hoffman et al (1994) not to be influenced by hypohydration to the extent of a body mass loss of up to 5.1% induced by exercise in the heat. In contrast, however, plasma noradrenaline concentration did respond to the hydration changes, which means that it may be possible to use this as a marker of hydration status, at least when induced by exercise in the heat.Urine indicesCollection of a urine sample for subsequent analysis has also been investigated and used as a hydration status marker.Measurement of urine osmolality has recently been an extensively studied parameter as a possible hydration status marker. In studies of fluid restriction, urine osmolality has increased to values greater than 900 mosm/kg for the first urine of the day passed in individuals dehydrated by 1.9% of their body mass, as determined by body mass changes (Shirreffs & Maughan, 1998). Armstrong et al (1994) have determined that measures of urine osmolality can be used interchangeably with urine-specific gravity, opening this as another potential marker.Urine colour is determined by the amount of urochrome present in it (Diem, 1962). When large volumes of urine are excreted, the urine is dilute and the solutes are excreted in a large volume. This generally gives the urine a very pale colour. When small volumes of urine are excreted, the urine is concentrated and the solutes are excreted in a small volume. This generally gives the urine a dark colour. Armstrong et al (1998) have investigated the relationshipTable 1 Examples of hydration status calculationsExercisePre-exercise Body massa (kg)Post-exercise Body massa (kg)Total body mass loss or gaind(ml or g)Drinks consumed during exerciseb (ml)Urine excreted during exercisec (ml)Sweat volume(ml)Hydration statusd(%)60 min Running 70.00 68.00 2000 0 200 1800 2.93 h Walking 70.00 70.00 0 500 400 100 0.0
2 h Cycling 70.0 0 70.20 þ 200 1000 0 800 þ 0.3

aBody mass measured nude with dry skin.
bDrinks consumed any time between the two bod