Lead Blood Levels and the Incidence of Essential Tumor, Essay Example

Health Outcome of Interest: Essential Tremor

Exposure(s) of Interest: Environmental toxins- in particular, lead

Diagnostic Criteria for Cases: The diagnostic criteria for cases was a diagnosis of essential tremor from the treating neurologist based on the presence of moderate amplitude action tremor of the arms or head tremor in the absence of other etiologies, such as Parkinson disease.

Case Ascertainment

This was a single site study based on diagnostic codes at Mersin University Hospital

Number of Cases (include information, if available, about the number who participated and the number who refused; indicate whether any information was provided about those who refused to participate):

There were originally 250 cases selected from the hospital’s directory; based on a random selection, 105 cases were ultimately selected.  The number of cases selected was based on sample size calculations.

Control Population  (type/number/selection)

There were a total of 105 controls selected.  The main reservoir for control selection was spouses of cases (n=69); if spouses were not available, a relative was selected who lived in the same district and was closest in age (n=36).  Eleven controls declined enrollment.

Type(s)/Method(s) of Data Collection (e.g. questionnaire, medical records, whether or not there was any procedure for validating some or the data):

There were three main sources of data in the case-control study: 1) clinical questionnaire (focusing on symptoms and clinical history); 2) videotaping of the cases to assess the tremor- this examination included one test to elicit postural tremor and five tests to elicit kinetic tremor.  3) Blood test of lead concentration levels.

Type of Data Analysis

There were two types of data analysis conducted: 1) A statistical analysis regarding blood lead concentrations; 2) Logistic regression analysis was then performed to test for a possible relationship between blood lead concentration (independent variable) and diagnosis of ET (case vs. control dependent variable).

Results/Main Findings of Study

Overall, results posited a possible association between increased lead levels measured in blood and the incidence of essential tumors. Blood lead concentrations were roughly doubled in ET cases compared with their counterparts without ET.  Even after controlling for other confounding factors, the association between the independent and dependent variable persisted.

Assessment of Bias (selection/information)

The only source of selection biased mention was seeking cases (and related controls) from one hospital- the only hospital in the region with essential tumor-related services.  Thus, the sample might not represent the general population.

Assessment of Confounders

The main limitation of the study was the cross-sectional study design.  Indeed, the study could only measure the blood lead concentrations at one point in time, and could not establish causality over a period of time.  Further potential confounders included: 1) occupation- the study only controlled for the current occupation and not past occupations; 2) dietary factors- vitamin C and iron have been reported with higher blood levels.

Comments

Overall, while the study did show heightened levels of blood lead in individuals with essential tumor, there will need to be more studies in order to establish the causality of this association.  These studies would be prospective in nature measuring the level of lead vis-à-vis the establishment of essential tumor.