HYD: Assessing Hydration Status (2007)


Francesconi RP, Hubbard RW, Szlyk PC, Schnakenberg D, Carlson D, Leva N, Sils I, Hubbard L, Pease V, Young J, Moore D.  Urinary and hematologic indexes of hypohydration.  J Applied Physiology 1987; 62(3): 1271-1276.

Study Design:
Diagnostic, Validity or Reliability Study
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To assess and quantitate the sensitivity of commonly used criteria of hypohydration.
Inclusion Criteria:

Adult M & F members of US Army units deploying to a field site as part of routine annual training cycle; informed consent.

Exclusion Criteria:
None mentioned.
Description of Study Protocol:

Recruitment: Adult M & F members of US Army units deploying to a field site as part of routine annual training cycle.Design: baseline body weight recorded before deployment; other measurements made in field detting on 1st, 20th, and 44th days of field deployment: 


First void urine, 25 mL: Usg: refractometry, immediately; Ucreat (spectrophotometer), Una, Uk (photometer) assayed later

Blood sample in fasted state: 10 ml; Hct (immediately, microhematocrit); serum Osm (freezing point depression); Urea N (serum), Screat.


Blinding used (if applicable):  not mentioned


Intervention (if applicable): n/a


Statistical Analysis: Group means compared for stat sig using Student's T-test; SIg at P<0.05; Usg >1.03 used as initial criterion of hypohydration; sg> 1.03 and body wt losses >3% may be categorized as hypohydrated




Data Collection Summary:

Timing of Measurements

 baseline body weight recorded before deployment; other measurements made in field detting on 1st, 20th, and 44th days of field deployment: 

Dependent Variables

  • Usg: refractometry, immediately;
  • Ucreat (spectrophotometer),
  • Una, Uk (photometer) assayed later
  • Blood sample Hct (immediately, microhematocrit);
  • serum Osm (freezing point depression);
  • Urea N (serum), Screat.




Description of Actual Data Sample:


Initial N: 230, M & F (17%F)

Attrition (final N): n/a

Age: not mentioned

Ethnicity: Not mentioned

Other relevant demographics: none mentioned

Anthropometrics: none mentioned

Location: Field site as part of routine annual training (specifics not mentioned)


Summary of Results:



All trials




T20 T44

Statistical Significance of Group Difference

SG <1.03







Creatinine w/SG criteria above






Una/k w/ SG Criteria above

 3.99± 0.1





Sosm w/ SG Criteria above  







P>0.05 for all
S Un/Creat w/SG criteria above  







T1: P=0.02

T20: P>0.05

T44: P=0.02

Hct w/SG criteria above  







P>0.05 for all


Other Findings

 Urine SG of >1.03 is indicative of hypohydration, impending hypohydration, or if transient, may be reflective of homeostatic adaptation to prevent debilitating hypohydration.

When body wt loss >3% was combined as criterion w/high SG, Ucreat were increased and Na/K values were attenuated when subjects losing <3% of body weight were compared. 

Consecutive urine samples with SG>1.03 may be clinically more evaluative.

Author Conclusion:
Mild hypohydration, manifested in concomitant elevations in urinary SG and creatinine was not reflected in common circulatory indices of hypohydration (Hct, Osm).  Alternatively, urea N -to -creatinine ratio may be a sensitive circulatory index of imminent hypohydration.
Funding Source:
Government: US Army
Reviewer Comments:
As an index of hypohydration, SG, logistically, can be assessed quickly and easily in field conditions, whereas other variables assessed required more complicated techniques/equipment. 
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
Validity Questions
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
2. Was the selection of study subjects/patients free from bias? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? No
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? N/A
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) N/A
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? ???
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) N/A
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? Yes
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) N/A
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? Yes
5. Was blinding used to prevent introduction of bias? Yes
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) Yes
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? ???
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? No
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes