Candidate gene case-control association studies advantages and potential pitfalls

Genome Biology for Genetic Epidemiologists Classical epidemiology deals with disease patterns and factors associated with causation of diseases with the ultimate aim of preventing the disease. Molecular epidemiologic studies measure exposure to specific substances DNA adducts and early biological response somatic mutationsevaluate host characteristics genotype and phenotype mediating response to external agents, and use markers of a specific effect like gene expression to refine disease categories such as heterogeneity, etiology and prognosis. Genetic epidemiology overlaps with molecular epidemiology.

Candidate gene case-control association studies advantages and potential pitfalls

Nevertheless, the blood smear remains a crucial diagnostic aid. The proportion of requests for a complete blood count that generate a blood smear is determined by local policies and sometimes by financial and regulatory as well as medical considerations.

For maximal information to be derived from a blood smear, the examination should be performed by an experienced and skilled person, either a laboratory scientist or a medically qualified hematologist or pathologist. In Europe, only laboratory-trained staff members generally "read" a blood smear, whereas in the USA, physicians have often done this.

Increasingly, regulatory controls limit the role of physicians who are not laboratory-certified. Nevertheless, it is important for physicians to know what pathologists or laboratory hematologists are looking for and should be looking for in a smear.

In comparison with the procedure for an automated blood count, the examination of a blood smear is a labor-intensive and therefore relatively expensive investigation and must be used judiciously.

A physician-initiated request for a blood smear is usually a response to perceived clinical features or to an abnormality shown in a previous CBC. A laboratory-initiated request for a blood smear is usually the result of an abnormality in the CBC or a response to "flags" produced by an automated instrument.

Less often, it is a response to clinical details given with the request for a CBC when the physician has not specifically requested examination of a smear. For example, a laboratory might have a policy of always examining a blood smear if the clinical details indicate lymphadenopathy or splenomegaly.

The International Society for Laboratory Hematology ISLH has published consensus criteria for the laboratory-initiated review of blood smears on the basis of the results of the automated blood count.

The indications for smear review differ according to the age and sex of the patient, whether the request is an initial or a subsequent one, and whether there has been a clinically significant change from a previous validated result referred to as a failed delta check.

All laboratories should have a protocol for the examination of a laboratory-initiated blood smear, which can reasonably be based on the criteria of the International Society for Laboratory Hematology. Regulatory groups should permit the examination of a blood smear when such protocols indicate that it is necessary.

There are numerous valid reasons for a clinician to request a blood smear, and these differ somewhat from the reasons why laboratory workers initiate a blood-smear examination.

Sometimes it is possible for a definitive diagnosis to be made from a blood smear. Clinical indications for examination of a blood smear: The presence of unexplained jaundice, particularly if unconjugated hyperbilirubinemia is also present, is an additional reason for a blood-smear examination.

Laboratory-initiated examinations of blood smears for patients with anemia are usually the result of a laboratory policy according to which a blood smear is ordered whenever the hemoglobin concentration is unexpectedly low.

This policy should be encouraged, since the consideration of the blood smear and the red-cell indices is a logical first step in the investigation of any unexplained anemia ref. Initiating a smear as a reflex test also means that a further blood sample does not have to be taken for this purpose.

Modern automated instruments impart valuable information about the nature of anemia. These variables usually include the RDW, which correlates on a blood smear with anisocytosis, and they may also include the hemoglobin-distribution width and the percentages of hypochromic and hyperchromic cells, which correlate with anisochromasia, hypochromia, and hyperchromia.


A variety of histograms and scatterplots give a visual representation of red-cell characteristics.An examination of the blood smear (or film) may be requested by physicians or initiated by laboratory staff.

With the development of sophisticated automated blood-cell analyzers, the proportion of blood-count samples that require a blood smear has steadily diminished and .

You have free access to this content Candidate gene case-control association studies: advantages and potential pitfalls. 1. INTRODUCTION Aim. The European Association of Urology (EAU) Guidelines Panel on Male Infertility has prepared these Guidelines to assist urologists and healthcare professionals from related specialties in the treatment of male infertility.

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GENETIC EPIDEMIOLOGY. Mehmet Tevfik DORAK. Genetic Epidemiology PowerPoint Presentation (PPT) Genetic Epidemiology Glossary. Bioinformatics for Genetic Epidemiologists Presentation (PPT) & Bioinformatics Tools. Genetic association studies are used to find candidate genes or genome regions that contribute to a specific disease by testing for a correlation between disease status and genetic variation.

focusing on case–control studies in candidate genes or regions.

Candidate gene case-control association studies advantages and potential pitfalls

Candidate gene association studies most commonly test for a difference in allele.

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