EAL

FL: Fluoride and the Renal System (2010)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

To assess the effect of chronic intake of high fluoride-rich water on plasma potassium levels of hemodialysed subjects.

Inclusion Criteria:

25 patients with chronic renal failure on heomdialysis on a continuing basis at Martigues Hospital between May 1993 and August 1996.

Exclusion Criteria:

None except not meeting inclusion criteria.

Description of Study Protocol:

Recruitment

At Martigues Hospital in France between May 1993 and August 1996.

Design

Retrospective observation of a group of subjects including some that consumed flouride-rich water and and some that did not.

Statistical Analysis

T-test, chi square, linear regression.

Data Collection Summary:

Timing of Measurements

Before and after dialysis.

Dependent Variables

Plasma potassium concentrations, by selective electrode of a CHEMI.

Independent Variables

Use of fluoride-rich water or not, plasma fluoride by selective electrode.

Control Variables

Stratification by before or after dialysis.

Description of Actual Data Sample:

Initial N: 25 (six in fluoride-rich water consumer group; 19 in non-consumer group)
Attrition (final N): 25 (retrospective observation so no loss to follow-up)
Age: Average 68.2 years in fluoride-rich water consumer group; average 61.1 years in non-consumer group
Other relevant demographics:
- 13 men, 12 women
- Duration on hemodialysis: Average 114.6 months in fluoride-rich water consumer group; average 57.7 months in non-consumer group
Location: France.

Summary of Results:

Kalemia before dialysis was significantly higher in the group that consumed high-fluoridated water than in group that did not (P<0.005). However, this difference was not significant after dialysis.
Regression coefficient for the relationship between plasma fluoride and potassium, of all subjects, before dialysis: 0.32 (P<0.0000001)
Regression coefficient for the relationship between plasma fluoride and potassium, of all subjects, after dialysis: 0.00317 (P=0.961)
Regression coefficient for the relationship between plasma fluoride and potassium, of fluoride-rich water consumers only, before dialysis: 0.472 (P<0.000005)
Regression coefficient for the relationship between plasma fluoride and potassium, of fluoride-rich water consumers only, after dialysis: 0.0692 (P=0.375).

Author Conclusion:

In dialysis patients, drinking water with a higher fluoride level is associated with the risk of hyperkalemia.

Funding Source:

Other:

not reported

Reviewer Comments:

Sample size was very small and uneven distribution between groups
Fluoride-rich water consumers had been on hemodialysis for a much longer time than non-consumers, but the difference wasn't significant, probably due to the small sample size. Not sure if this would be a potential confounder.
Data collection process was not blinded
Statistical methods were weak. They could have run a regression with before/after dialysis as a covariate.
Duration and amount of fluoride-rich water consumption was not described
How patients decided on drinking fluoride-rich water or not was not described. There could be residual confouding.

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?		No
	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
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	No
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)	No
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	Yes
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	???
	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?	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.)	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
	4.1.	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?	N/A
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.)	No
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	No
	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
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		No
	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?	No
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	???
	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?	Yes
	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
	7.1.	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?	???
	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?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		No
	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?	No
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	No
	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?	No
	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?	No
10.	Is bias due to study's funding or sponsorship unlikely?		???
	10.1.	Were sources of funding and investigators' affiliations described?	No
	10.2.	Was the study free from apparent conflict of interest?	???