Exposure to Low-Dose Ionizing Radiation from Medical Imaging Procedures
Reza Fazel, M.D., M.Sc., Harlan M. Krumholz, M.D., S.M., Yongfei Wang, M.S., Joseph S. Ross, M.D., Jersey Chen, M.D., M.P.H., Henry H. Ting, M.D., M.B.A., Nilay D. Shah, Ph.D., Khurram Nasir, M.D., M.P.H., Andrew J. Einstein, M.D., Ph.D., and Brahmajee K. Nallamothu, M.D., M.P.H.
ABSTRACT
Background The growing use of imaging procedures in the United States has raised concerns about exposure to low-dose ionizing radiation in the general population.
Methods We identified 952,420 nonelderly adults (between 18 and 64 years of age) in five health care markets across the United States between January 1, 2005, and December 31, 2007. Utilization data were used to estimate cumulative effective doses of radiation from imaging procedures and to calculate population-based rates of exposure, with annual effective doses defined as low (3 mSv), moderate (>3 to 20 mSv), high (>20 to 50 mSv), or very high (>50 mSv).
Results During the study period, 655,613 enrollees (68.8%) underwent at least one imaging procedure associated with radiation exposure. The mean (±SD) cumulative effective dose from imaging procedures was 2.4±6.0 mSv per enrollee per year; however, a wide distribution was noted, with a median effective dose of 0.1 mSv per enrollee per year (interquartile range, 0.0 to 1.7). Overall, moderate effective doses of radiation were incurred in 193.8 enrollees per 1000 per year, whereas high and very high doses were incurred in 18.6 and 1.9 enrollees per 1000 per year, respectively. In general, cumulative effective doses of radiation from imaging procedures increased with advancing age and were higher in women than in men. Computed tomographic and nuclear imaging accounted for 75.4% of the cumulative effective dose, with 81.8% of the total administered in outpatient settings.
Conclusions Imaging procedures are an important source of exposure to ionizing radiation in the United States and can result in high cumulative effective doses of radiation.
http://content.nejm.org/cgi/reprint/361/9/849.pdf
Saturday, August 29, 2009
Allergen-Specific IgE Antibody
The protein of the blood is composed of albumin and globulins. One type of globulin is the group of gamma globulins, also called immunoglobulins or antibodies. Gamma globulins are produced by certain white blood cells known as B lymphocytes in response to stimulation by antigens. There are five types of immunoglobulins:
IgA, IgD, IgE, IgG, and IgM. IgE is the antibody of allergies.
Testing for allergies to various substances can be done via skin testing, however, this can be uncomfortable for the patient and carries the risk of causing an allergic reaction, since allergens are actually introduced into the body. Another way to test for such allergies is the allergen-specific IgE antibody test. This test is also called the radioallergosorbent test, or RAST test, because it involves the use of fluorescent immunoassay to identify the specific allergens that are affecting the person. The specific antigens, or allergens, are bound to a carrier substance. If the person is allergic to a particular allergen, a specific IgE antibody in the person’s blood sample will react with the allergen.
IgA, IgD, IgE, IgG, and IgM. IgE is the antibody of allergies.
Testing for allergies to various substances can be done via skin testing, however, this can be uncomfortable for the patient and carries the risk of causing an allergic reaction, since allergens are actually introduced into the body. Another way to test for such allergies is the allergen-specific IgE antibody test. This test is also called the radioallergosorbent test, or RAST test, because it involves the use of fluorescent immunoassay to identify the specific allergens that are affecting the person. The specific antigens, or allergens, are bound to a carrier substance. If the person is allergic to a particular allergen, a specific IgE antibody in the person’s blood sample will react with the allergen.
Aldolase
Aldolase is a glycolytic enzyme that is present in all body cells. The highest concentrations of aldolase are found in the cells of skeletal muscles, the heart, and liver tissue, although the test is considered most specific for muscle tissue destruction.
When damage to muscle tissue occurs, cells are destroyed, resulting in the release of aldolase into the blood. Thus, testing for aldolase is useful in monitoring the progress of muscle damage in such disorders as muscular dystrophy.
When damage to muscle tissue occurs, cells are destroyed, resulting in the release of aldolase into the blood. Thus, testing for aldolase is useful in monitoring the progress of muscle damage in such disorders as muscular dystrophy.
Aldosterone
Aldosterone is a mineralocorticoid secreted by the adrenal cortex. The release of aldosterone is controlled primarily by the renin-angiotensin-aldosterone system. A decrease in extracellular fluid results in decreased blood flow through the kidneys, which in turn stimulates production and secretion of renin by the kidneys. Renin acts on angiotensinogen to form Angiotensin I which, in the presence of angiotensinconverting enzyme (ACE), is converted to Angiotensin II. Angiotensin II stimulates the adrenal cortex to increase aldosterone production. The effects of aldosterone occur in the renal distal tubule, where it causes increased reabsorption of sodium and chloride and increased excretion of potassium and hydrogen ions. The result of these actions is retention of increased water and an increase in extracellular fluid. The ultimate effect of changes in aldosterone level is regulation of blood pressure.
Measurement of aldosterone level is performed on both the plasma and the urine. This information assists in the diagnosis of primary aldosteronism, caused by an abnormality of the adrenal cortex, and of secondary aldosteronism, which may result from overstimulation of the adrenal cortex by a substance such as angiotensin or ACTH.
Measurement of aldosterone level is performed on both the plasma and the urine. This information assists in the diagnosis of primary aldosteronism, caused by an abnormality of the adrenal cortex, and of secondary aldosteronism, which may result from overstimulation of the adrenal cortex by a substance such as angiotensin or ACTH.
Alanine Aminotransferase
Alanine aminotransferase (ALT) is an enzyme found in the kidneys, heart, and skeletal muscle tissue but primarily in liver tissue. It functions as a catalyst in the reaction needed for amino acid production. The test is used mainly in the diagnosis of liver disease and to monitor the effects of hepatotoxic drugs. ALT is assessed along with asparate aminotransferase (AST) in monitoring liver damage. These two values normally exist in an approximately 1:1 ratio. The AST is greater than the ALT in alcohol-induced hepatitis, cirrhosis, and metastatic cancer of the liver. ALT is greater than AST in the case of viral or drug-induced hepatitis and hepatic obstruction due to causes other than malignancy. The degree of increase in these enzyme levels provides information as to the possible source of the problem. A twofold increase is suggestive of an obstructive problem, often requiring surgical intervention. A 10-fold increase of ALT and AST indicates a probable medical problem such as hepatitis.
Adrenocorticotropic Hormone
In response to a stimulus such as stress, the hypothalamus secretes corticotropinreleasing hormone. This hormone stimulates the secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary gland. ACTH, in turn, causes the adrenal cortex to release the glucocorticoid hormone cortisol. As levels of cortisol in the blood rise, the pituitary gland is stimulated to decrease ACTH production via a negative feedback mechanism. (See Appendix B for description of hormonal feedback process).
Diurnal variations in ACTH levels occur, with peak levels occurring between 6 and 8 AM and trough levels occurring between 6 and 11 PM. Trough levels are approximately one-half to two-thirds the peak levels. Assessment of ACTH levels is used in conjunction with knowledge of cortisol levels to evaluate adrenal cortical dysfunction. For example, consider the patient with Addison’s disease in which the adrenal cortex is hypoactive, thus producing abnormally low levels of cortisol in the blood. The anterior pituitary gland senses the low serum cortisol levels and, as a result, increases its release of ACTH. This is an attempt to stimulate the adrenal gland to increase its production of cortisol. Thus, the combination of high ACTH and low cortisol levels indicates adrenocortical hypoactivity. Conversely, if the adrenal gland is overproducing cortisol, as in the presence of an adrenal tumor, the ACTH level will be low as the anterior pituitary gland responds to the elevated cortisol level. Should there be a high level of ACTH due to a pituitary tumor or a nonendocrine ACTH-producing tumor, there will also be an elevated cortisol level, as the adrenal gland responds to stimulation by the ACTH.
Diurnal variations in ACTH levels occur, with peak levels occurring between 6 and 8 AM and trough levels occurring between 6 and 11 PM. Trough levels are approximately one-half to two-thirds the peak levels. Assessment of ACTH levels is used in conjunction with knowledge of cortisol levels to evaluate adrenal cortical dysfunction. For example, consider the patient with Addison’s disease in which the adrenal cortex is hypoactive, thus producing abnormally low levels of cortisol in the blood. The anterior pituitary gland senses the low serum cortisol levels and, as a result, increases its release of ACTH. This is an attempt to stimulate the adrenal gland to increase its production of cortisol. Thus, the combination of high ACTH and low cortisol levels indicates adrenocortical hypoactivity. Conversely, if the adrenal gland is overproducing cortisol, as in the presence of an adrenal tumor, the ACTH level will be low as the anterior pituitary gland responds to the elevated cortisol level. Should there be a high level of ACTH due to a pituitary tumor or a nonendocrine ACTH-producing tumor, there will also be an elevated cortisol level, as the adrenal gland responds to stimulation by the ACTH.
Adrenocorticotropic Hormone Stimulation Test
The hypothalamus secretes corticotropin-releasing hormone. This hormone stimulates
the secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary
gland. ACTH, in turn, causes the adrenal cortex to release the glucocorticoid hormone
cortisol. Problems occurring in the adrenal cortex are considered “primary”
disorders, whereas those occurring in the anterior pituitary gland are known as “secondary” disorders. It is important to determine whether a patient’s problem is of a primary or a secondary nature.
Various tests may be used to evaluate adrenal hypofunction through stimulation of the adrenal glands. The most common is the rapid ACTH test, for which cosyntropin Cortrosyn) is administered. ACTH stimulation testing is especially valuable in the diagnosis of Addison’s disease. If plasma cortisol levels increase after administration of ACTH, the adrenal gland has the ability to function when stimulated and the cause of the adrenal insufficiency would be due to a problem in the pituitary gland. If, however, the plasma cortisol levels do not rise or increase only minimally, the problem lies with the adrenal gland. The test can also be used to check for recovery of the hypothalamus-pituitary-adrenal (HPA) axis during tapering of steroids after long-term use.
the secretion of adrenocorticotropic hormone (ACTH) by the anterior pituitary
gland. ACTH, in turn, causes the adrenal cortex to release the glucocorticoid hormone
cortisol. Problems occurring in the adrenal cortex are considered “primary”
disorders, whereas those occurring in the anterior pituitary gland are known as “secondary” disorders. It is important to determine whether a patient’s problem is of a primary or a secondary nature.
Various tests may be used to evaluate adrenal hypofunction through stimulation of the adrenal glands. The most common is the rapid ACTH test, for which cosyntropin Cortrosyn) is administered. ACTH stimulation testing is especially valuable in the diagnosis of Addison’s disease. If plasma cortisol levels increase after administration of ACTH, the adrenal gland has the ability to function when stimulated and the cause of the adrenal insufficiency would be due to a problem in the pituitary gland. If, however, the plasma cortisol levels do not rise or increase only minimally, the problem lies with the adrenal gland. The test can also be used to check for recovery of the hypothalamus-pituitary-adrenal (HPA) axis during tapering of steroids after long-term use.
Acid Phosphatase
Acid phosphatase, also known as prostatic acid phosphatase (PAP), is an enzyme found primarily in the prostate gland, with high concentrations found in the seminal fluid. It is found in smaller concentrations in the kidneys, liver, spleen, bone marrow, erythrocytes, and platelets. Acid phosphatase is used to diagnose advanced metastatic cancer of the prostate and to monitor the patient’s response to therapy for prostate cancer. In the past, this test has been considered a tumor marker for prostatic cancer. However, with the advent of the prostate-specific antigen (PSA) test, monitoring of the acid phosphatase is decreasing in popularity. An additional use of acid phosphatase testing is testing for its presence in vaginal secretions during the investigation of cases of alleged rape.
Acid-Fast Bacilli
The acid-fast method is a special staining technique that is particularly useful when identifying mycobacteria in sputum specimens, which often contain a variety of organisms. Examples of mycobacteria are those causing leprosy, tuberculosis, and respiratory infection in patients with acquired immunodeficiency syndrome (AIDS). Mycobacteria retain stain coloring even after treatment with a decolorizing acidalcohol solution. Once bacilli are determined to be acid-fast, a culture is done to differentiate the type of mycobacteria, along with sensitivity testing to determine appropriate pharmacologic treatment.
Acid-Fast Bacilli
The acid-fast method is a special staining technique that is particularly useful when identifying mycobacteria in sputum specimens, which often contain a variety of organisms. Examples of mycobacteria are those causing leprosy, tuberculosis, and respiratory infection in patients with acquired immunodeficiency syndrome (AIDS). Mycobacteria retain stain coloring even after treatment with a decolorizing acidalcohol solution. Once bacilli are determined to be acid-fast, a culture is done to differentiate the type of mycobacteria, along with sensitivity testing to determine appropriate pharmacologic treatment.
Acetylcholine Receptor Antibodies
Acetylcholine (ACh) and the catecholamines (epinephrine and norepinephrine) are the main neurotransmitters of the autonomic nervous system. In normal contraction of the muscles, ACh is released from the terminal end of the nerve into the neuromuscular junction. ACh then binds with receptor sites on the muscle membrane, resulting in the opening of sodium channels. This allows sodium ions to enter and depolarize the cell. This begins an action potential that passes along the entire muscle fiber, resulting in muscle contraction.
Myasthenia gravis (MG) is an autoimmune disease that affects neuromuscular transmission. In this disease, antibodies form that interfere with the binding of ACh to the receptor sites on the muscle membrane. This prevents muscle contraction from occurring. These antibodies are present in more than 85% of the patients with MG. Thus, this test is used for diagnosis of MG and for monitoring the patient’s response to immunosuppressive therapy for the disease.
Myasthenia gravis (MG) is an autoimmune disease that affects neuromuscular transmission. In this disease, antibodies form that interfere with the binding of ACh to the receptor sites on the muscle membrane. This prevents muscle contraction from occurring. These antibodies are present in more than 85% of the patients with MG. Thus, this test is used for diagnosis of MG and for monitoring the patient’s response to immunosuppressive therapy for the disease.
