HYD: Assessing Hydration Status (2007)


Ship JA, Fischer DJ. Metabolic indicators of hydration status in the prediction of parotid salivary-gland function. Archives of Oral Biology. 1999 Apr;44(4):343-50

PubMed ID: 10348361
Study Design:
Diagnostic, Validity or Reliability Study
C - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
To determine whether metabolic indicators of body hydration status could be predictive for parotid salivary flow rates in a population of healthy adults
Inclusion Criteria:

Healthy participants

  • not taking any non-prescription or prescription medications within the previous 7 days with the exception of birth-control medications and hormone replacement therapy
  • not currently being treated for any systemic disease
  • absence of salivary gland pathology/disease
  • evidence of unstimulated parotid function
  • no history of treatment for head and neck cancer
  • completion of a consent form
Exclusion Criteria:
None reported
Description of Study Protocol:


 No data


 Study of sensitivity and specificity of a diagnostic test (prospective design)

Blinding used (if applicable)

 No data

Intervention (if applicable)

No eating, drinking, amoking, or performing any oral hygiene for >90 min before entry intot the study. Participants were weighed after emptying his/her bladder. Unstimulated and stimulated parotid salivas and a blood sample were then collected. Participants refrained from drinking any beverages and eating any foods for 24 hrs, and also avoided any exercise or strenuous activity during the course of the study. All urine was collected for the 24-h dehydration period. Next day, the same procedure was repeated. The loss in weight (kg) over the 24 h of fluid and food restriction was used as the amount of replacement fluid (1 kg = 1 litter) to be given to each participant (1000 ml/h). At the completion of testing, the participant was provided with food and beverages ad libitum.

No participant experienced clinical signs or symptoms of dehydration, and therefore there was no need to terminate dehydration in any of them.

Statistical Analysis

  • Correlation coefficients (r) and coefficients of determination (r2). A significance level of P=0.05 was used. Bonferroni correction was used to adjust for multiple testing. The P value for each group of correlations between salivary and metabolic variables was 0.05/81=0.0006. The P value for each group of comparisons of salivary flow rates with each corresponding metablic factor was 0.05/23=0.002.
  • Multiple Student t-tests with Bonferroni correction.
Data Collection Summary:

Timing of Measurements

 Baseline (pre-dehydration), 24 hr (completion of dehydration); 27 hr (completion of rehydration)

Dependent Variables

  • Unstimulated and stimulated parotid flow rate: All parotid salivary samples were collected in the same manner by 2 examiners. Parotid saliva was collected by placing a modified Carlson-Crittenden cup over the orifice of one parotid gland. 2% citric acid was used for stimulation. Unstimultaed and stimulated parotid salivas were collected at 1-hr intervals.
  • Haematocrit (%): Intravenous blood sample was taken after the saliva collection. Haematocrit was calculated by Coulter counter.
  • Haemoglobin (g/dl): Intravenous blood sample was taken after the saliva collection. Haemoglobin was measured spectrophotometrically, using a GenS Coulter Counter.
  • Concentrations of total proteins, sodium, creatinine, serum osmolality, and urinary osmolality were measured by standard clinical laboratory techniques.

Independent Variables

 24 hour dehydration; then rehydration

Control Variables


Description of Actual Data Sample:


Initial N: 12 young adults (50% male); 12 older adults (50% males)

Attrition (final N): 24

Age: Young adults=26.05 (range 20-29); Older adults=70.4 (range 62-76)

Ethnicity: No data

Anthropometrics: Body weight: Male=84.1 kg; Females=68.5 kg

Location: US


Summary of Results:
 I. Parotid flow rates, haematocrit, haemoglobin, and body weight

Salivary and metabolic variables
Baseline (Pre-dehydration)
24 hrs (Completion of dehydration)
27 hrs (Completion of rehydration)
Unstimulated parotid flow rate (ml/min)
Stimulated parotid flow rate (ml/min)
Haematocrit (%)
Haemoglobin (g/dl)
Body weight (kg)

*p<0.05, compared to baseline value
**p<0.001, compared to baseline value

 II. Correlation analyses

There was no statistically significant correlations were observed for the relationships between the level of hydration (aseessed with the 7 metabolic variables) and body weight and the unstimulated and stimulated salivary flow rates at baseline, 24 hrs and 27 hrs.


Author Conclusion:

Based on the our results, metabolic indicators of hydration status are not accurate predictors of parotid salivary flow.

No consistent correlation between salivary flow rates and metabolic variables or body weight.

Our data suggest that in healthy adults, age does not have a major role in the relation between hydration and saliva output.

Funding Source:
Government: National Institute of Dental Research
University/Hospital: University of Michigan
Foundation associated with industry:
Reviewer Comments:


No participant experienced clinical signs or symptoms of dehydration, and there was no "gold standard" measure for dehydration. Therefore, it is also possible thatthe duration of dehydration was insufficient to elucidate a relation between metabolic markers of hydration status and salivary output.

Healthy yound and older unmedicated adults only.

Sample size may be too small to detect a small alpha level due to Bonferroni corrections.

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) N/A
  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? Yes
  2.2. Were criteria applied equally to all study groups? N/A
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
3. Were study groups comparable? No
  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? N/A
  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")? No
4. Was method of handling withdrawals described? Yes
  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? N/A
  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? No
  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.) N/A
  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? No
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? N/A
  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? No
  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? N/A
  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? No
  7.1. Were primary and secondary endpoints described and relevant to the question? No
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? ???
  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? No
  7.7. Were the measurements conducted consistently across groups? N/A
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? No
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