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Hydration

HYD: Assessing Hydration Status (2007)

Citation:
Dauterman KW, Bennett RG, Greenough WB, Redett RJ, Gillespie JA, Applebaum G, Schoenfeld CN. Plasma specific gravity for identifying hypovolaemia. J Diarrhoeal Dis Res 1995 Mar;13(1):33-8. PubMed ID: 7657963
 
Study Design:
Prospective, observational study
Class:
C - Click here for explanation of classification scheme.
Quality Rating:
Positive POSITIVE: See Quality Criteria Checklist below.
Research Purpose:
To define ranges of plasma specific gravity useful for identifying volume depletion in older adults.
Inclusion Criteria:

Group 1: House officers at JH Hospital; male or female; not screened for acute or chronic illnesses

Group 2: adults >65 years of age, male and female, visiting the medical center in their retirement community

Group 3: >65 years of age, male and female; acutely ill and visiting ED; most seen for evaluation of febrile illnesses or exacerbation of underlying chronic disease

Exclusion Criteria:

Group 1: none

Group 2: without acute or volume-depleting illness

Group 3:  none

Description of Study Protocol:

Recruitment

Group 1: 170 young adults, male and female house officers at Johns Hopkins Hospital undergoing outine new employee lab testing
Group 2: 10-0 retirees, equal to or over 65 years of age, without acute or volume depleting illness who went for medical care to a medical center within their retirement community
Group 3: 68 adults, equal to or over 65 years of age, recruited from among actuely ill patients treated in the ED of Francis Scott Key Medical Center in Baltimore

Group 1 and 2 employed an over-sampling and Group 3 represented a convenience sampling.

Design

Excess venous blood was drawn for all participants and appropriately collected for determination of plasma specific gravity. Plasma refractive index for each sample was measured with a hand-held refractometer. The index was thn converted to plasma specific gravity using a conversion table.

Blinding used (if applicable) Not applicable

 Intervention (if applicable) Not applicable

 Statistical Analysis

Plasma specific gravity for each of the three groups was analyzed using chi-square goodness-of-fit tests to determine norms. Since the values for all groups were not normally distributed, frequency distributions were plotted, and only the median and range values for each group were determined. Comparisons of groups were made using Mann-Whitney two sample tests to determine whether the older ED patients had higher values (more volume depletion) compared to the other two groups.

Six plasma specific gravity ranges were defined including <1.0234, 4 ranges between 1.0235 and 1.0294 (where the majority of values fit), and >1.0295. The three highest ranges were designated in ascending order as possible volume depletion, probable volume depletion and definite volume depletion.

 

Data Collection Summary:

Timing of Measurements

Group 1:  Blood collected  in July 1992

Group 2: Blood collected between September and October 1991

Group 3: Blood collected between in July 1991

 Dependent Variables

  • Specific Plasma Gravity values as defined by their inclusion in six different range categories

 Control Variables

  • Assumed to be without volume depleting conditions at the time of testing

 

Description of Actual Data Sample:

 

Initial N: Group 1: 170   Group 2: 100  Group 3: 68

Attrition (final N): No attrition

Age: Group 1: Mean age 28 years (range 23-44)  Group 2: mean age 81 years (range 67-91)  Group 3:  Mean age 74 (range 65-91)

Gender: Group 1: 92 M (54%) / 78 F (46%)   Group 2: 22 M (22%) / 78 F (78%)    Group 3: 29 M (43%) / 39 F (57%)

Ethnicity: Not identified

Anthropometrics:  There were more older individuals in Group 2, the older control group than in Group 3, the older adults treated in the ED.  Group 1 had a significantly higher male population than either of the two older groups.

Location: Group 1: recruited from Johns Hopkins Medical Center in Baltimore, MD, Group 2: recruited from the Charlestown  Retirement Community, Catonsville, MD  Group 3: Recruited from the ED of Francis Scott Key Medical Center, Baltimore, MD  

 

 

Summary of Results:

Plasma Specific Gravity Levels in Young and Old Control Groups and Older ER patients

Population

Outcomes

Plasma Specific Gravity, mg.dl

Median/range

 Group 1

1.0262    

(1.0235-1.0289)

0% Volume depleted;5% probably volume depleted;27% possibly volume depleted

Group 2

 

 

 

 

Group 3

1.0255

(1.0221-1.0289)

0% Volume depleted; 8% probably volume depleted; 12% possibly volume depleted

1.0268

(1.0221-1.0310)

15% Volume depleted; 21% probably volume depleted; 33% possibly volume depleted

 

Other Findings

The plasma specific gravity (PSG) values for the young and old control groups did not differ significantly.  However, the values for the ED patients were significantly greater when compared to the young control group (p=0.0022) and the older control group (p<0.0001). 

The numbers of ED patients vs. young adults with possible volume depletion did not differ significantly but there was a significant difference in possible volume depletion between the ED patients and the older controls p=0.00001

The numbers of ED patients vs. young adults with probable volume depletion differed significantly (p=0.0006) and vs. older adults the ED patients also differed significantly (p=0.03).

And finally, the numbers of ED patients with definite volume depletion vs. both young and older adults differed significantly by 0.00001.

 Limitations of the Study

Serial measurements of ED patient serum specific gravity were not done to show that plasma specific gravity decreased with hydration. 

Clinical data on ED patients was not collected.   This would have identified the number of ED patients who had illness-related fever and anorexia, diuretic overuse, gastroenteritis, increased BUN and Creatinine, etc, which may correlate with volume depletion.

Also, correlation of PSG with total serum protein would have shown the actual degree to which baseline hypoproteinemia affected the PSG values in both groups of elderly participants.  This would have clarified the problem of having plasma specific gravity values in the retirees (Group 2) skewed toward lower values, suggesting that individuals with low plasma protein were included in the old control group.

Author Conclusion:

However, there are limitations of the test, which must be considered. These include the following:

  • PSG can be high without volume depletion in patients with multiple myeloma or hypergammaglobulinemia
  • PSG can be low with volume depletion in patients with nephrotic syndrome, liver failure, malnourishment or hypoproteinemia, problems often present in the elderly population

Patients who are bleeding internally may be severely volume depleted without demonstrating an elevated PSG

Funding Source:
University/Hospital: John Hopkins School of Medicine
Reviewer Comments:
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
  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
  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
  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
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) Yes
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? N/A
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? N/A
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? Yes
  1.3. Were the target population and setting specified? Yes
  2. Was the selection of study subjects/patients free from bias? 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
  2.1. 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? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? Yes
  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
  2.4. Were the subjects/patients a representative sample of the relevant population? Yes
  3. Were study groups comparable? Yes
3. Were study groups comparable? Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) Yes
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? 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.) Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  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? Yes
  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? Yes
  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.) No
  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.) No
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  4. Was method of handling withdrawals described? N/A
4. Was method of handling withdrawals described? N/A
  4.1. Were follow-up methods described and the same for all groups? N/A
  4.1. 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
  4.2. 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
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? N/A
  4.4. Were reasons for withdrawals similar across groups? N/A
  4.4. 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? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  5. Was blinding used to prevent introduction of bias? N/A
5. Was blinding used to prevent introduction of bias? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  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
  5.2. 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
  5.3. 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
  5.4. 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? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  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
  6.2. 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? N/A
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.6. 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
  6.7. 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? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  7. Were outcomes clearly defined and the measurements valid and reliable? 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
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? N/A
  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? N/A
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? N/A
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? 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? N/A
  7.5. Was the measurement of effect at an appropriate level of precision? N/A
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? Yes
  7.7. Were the measurements conducted consistently across groups? 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. 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
  8.1. 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
  8.2. 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
  8.3. 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
  8.4. 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)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? N/A
  8.6. Was clinical significance as well as statistical significance reported? Yes
  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
  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? N/A
9. Are conclusions supported by results with biases and limitations taken into consideration? N/A
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? 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. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes