Clinical Assessment - Laboratory Tests
Course: WB 2460
CE Original Date: May 14, 2014
CE Renewal Date: May 14, 2016
CE Expiration Date: May 14, 2018
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Upon completion of this section, you will be able to
- Describe measurements that can help diagnose exposure to PCBs.
The lipophilic nature of PCBs causes them to accumulate in fat; consequently, analyzing biopsied adipose tissue has been used to measure long-term exposure.
Serum PCB analysis is less invasive than tissue biopsy, and it can be performed by most commercial reference laboratories. Although such tests are useful for gauging exposure, they may not be consistent with adverse health effects.
Select laboratories have the capability to perform PCB analyses on human tissue. Testing human tissue for PCB content, however, remains principally a research tool.
PCBs have been detected in the blood, adipose tissue, and breast milk of non-occupationally exposed members of the general population [CDC 2009; EPA 1986b; Greizerstein et al. 1999; Gunderson and Gunderson 1995; Patterson et al. 2008]. Since the United States stopped making PCB compounds, body burdens of PCBs in humans have decreased. This decrease is evidenced by lower PCB levels reported in human adipose tissue, blood serum, and breast milk [Anderson et al. 1998; Fensterheim 1993; Hanrahan et al. 1999; Lunden et al. 1998; Schade et al. 1998].
PCB compounds generally can be found at the parts per trillion (ppt) levels in the lipid stores of humans, especially persons living in industrialized societies. The general population is exposed to PCB compounds primarily by ingesting high-fat foods, such as
- Dairy products,
- Animal fats, and
- Some fish and wildlife [CDC 2009; Patterson et al. 2008].
However, no specified PCB values are deemed normal or toxic levels.
Some researchers believe that PCB levels in the serum and tissue provide a reliable measurement of long-term exposure. PCB levels in the serum and tissue can be measured by many laboratories although analyses results may not be consistent with health effects.
A correlation between increasing levels of serum PCBs and dermatologic findings, including chloracne, has not been found consistently in human epidemiologic studies. However, statistically significant associations between dermatologic effects and plasma levels of higher chlorinated PCB congeners have been reported [Fischbein et al. 1982; Fischbein et al. 1979; Smith et al. 1982].
Although PCBs accumulate in breast milk, the American Association of Pediatrics (AAP) has concluded that the risks posed by PCBs in breast milk are outweighed by the benefits of breastfeeding in all but the most unusual circumstances. Therefore, AAP does not recommend that breast milk be tested for PCBs because the test results would not likely change the recommendation to breast feed. Additionally, AAP recommends consulting local health department officials who are aware of the PCB problems in unusual circumstances or where high exposures have occurred [AAP 2003].
Liver function tests are nonspecific.
The combination of asymptomatic hepatomegaly and mild, nonspecific elevations of hepatic enzymes suggests a chronic inflammatory liver process or hepatitis. Hepatitis can be
- Caused by ethanol ingestion, or
- Associated with connective tissue disease.
The major cause of liver disease in the United States is ethanol ingestion. Less common causes are environmental exposures, resulting in either acute or chronic toxic hepatitis.
Infectious hepatitis includes disease caused by viruses such as A, B, C, and other possible agents of non-A, non-B hepatitis. Hepatitis can also occur with Epstein-Barr virus and cytomegalovirus infections. Some connective tissue diseases such as lupus erythematosus are associated with a specific type of hepatitis. Infiltrative diseases such as sarcoidosis or amyloidosis, and rare genetic diseases such as Wilson disease, primary hemochromatosis, and alpha-1-antitrypsin deficiency, must be excluded.
Normal liver enzyme values do not rule out significant PCB exposure; body burden still might be elevated.
To help arrive at a diagnosis, viral serology and a heterophil antibody test should be considered. If the patient has suggestive signs or symptoms, a serum iron and total iron binding capacity, serum copper and ceruloplasmin, and antinuclear antibodies might help with the diagnosis. Assays for suspected hepatotoxins might also be useful. If other tests do not provide sufficient information, further evaluation might include ultrasound and percutaneous liver biopsy.
- Serum or adipose tissue PCB levels can indicate exposure, but they are difficult to interpret clinically.
- AAP does not recommend testing breast milk for PCBs, and encourages breastfeeding in all but the most unusual circumstances.
- Elevated hepatic enzyme levels are of limited value in diagnosing exposure to PCBs.