Screening for Liver and Kidney Disease

Exposure to hazardous or toxic substances can affect the body in many ways. In general, when chemicals and other hazardous substances are absorbed, they travel through the various body systems and can affect a particular organ or organs, called the “target organ(s).” Fortunately, the body has mechanisms, mainly in the liver and kidneys, to process and eliminate many of these substances. This ability to eliminate toxic substances can reduce the effect(s) on the target organ(s).

The elimination of toxic substances is just one of the many functions of the liver and kidneys. For example, the kidneys maintain the blood volume and regulate the mineral content in the bloodstream. The liver converts nutrients into energy, forms proteins and stores carbohydrates. While these organs can be remarkably resilient in the elimination of toxins, their other functions can be damaged in the process.

Damage to the kidney and liver can be acute or chronic. An acute process generally refers to a relatively short period of time (hours to weeks) between exposure to the toxin and the onset of symptoms or medical findings. A chronic process generally refers to a long period of time (years) between exposure to the toxin and the onset of symptoms or medical findings. The detection of either an acute or chronic process or disease can be complex, depending on the type of toxin and the extent of exposure.

How Do You Detect Liver or Kidney Disease?
Medical screening to detect chronic liver and kidney disease usually involves a test that measures how well these organs are functioning, rather than testing for the toxic substance itself. While there are several reasons for this approach, the main reason is that many substances that cause chronic disease of the liver and kidney are difficult to detect in the body.

There are several tests available to detect abnormalities. Blood tests --- commonly referred to as liver and kidney function tests --- are among the most commonly used. In a typical blood chemistry profile, six liver function and two kidney function tests are done.   See box.

What are Liver Function Tests?
Text Box: Graphic here re: enzymes All of the liver function tests, with the exception of bilirubin, are measurements of enzyme levels. These enzymes are normally present in liver cells, and there is a certain “normal” level of these enzymes circulating in the bloodstream. When the liver becomes inflamed or damaged, these enzymes are released into the bloodstream in abnormal amounts by the damaged cells. This results in elevated levels in the bloodstream. Bilirubin, another substance commonly measured in the blood to detect liver disease, is produced from the breakdown of red blood cells. Again, a normal bilirubin level is maintained as the liver continually removes bilirubin from the bloodstream for further processing. If the liver is impaired, however, bilirubin is not removed, and the level in the bloodstream will rise.

What are Kidney Function Tests?
The kidney function tests do not measure enzymes, but measure breakdown products of normal body processes. Blood urea nitrogen (BUN) is produced as a result of protein breakdown. BUN is formed in the liver and carried via the bloodstream to the kidneys to be eliminated. Creatinine is a breakdown product of a specific type of muscle protein. It is formed in certain muscles and is carried via the bloodstream to be eliminated by the kidneys. If the kidneys become impaired and unable to eliminate the usual amount of these substances, the BUN and creatinine blood levels will rise.

Liver Function Tests Kidney Function Tests
Alanine aminotransferase (ALT) Blood urea nitrogen (BUN)
Aspartate aminotransferase (AST) Creatinine
Gamma glutamic transpeptidase (GGT)  
Lactic dehydrogenase (LD or LDH)  
Alkaline phosphatase (ALP)  

What if These Tests are Elevated?
If either a liver or a kidney function test is elevated, then the next step is to determine what is causing the elevation. It is important to remember that elevated liver or kidney tests are not diagnoses in themselves but rather serve as indicators of abnormal function of these organs.

There are many diseases and conditions that can cause an elevation of these tests. Some of the more common causes are hepatitis (inflammation of the liver) from infectious agents such as viruses and substances such as alcohol. Some common causes of kidney damage include diabetes and high blood pressure. Kidney and liver damage may also be work-related. There are certain organic chemicals (such as carbon tetrachloride) that can cause both liver and kidney disease. Certain metals (lead, mercury, cadmium and uranium) are known to cause chronic kidney disease. Since many toxic substances are difficult to detect in the body, a detailed occupational history is essential for determining whether kidney or liver disease is work-related.

Liver and kidney function tests, once documented to be elevated, need to be monitored periodically, depending on the degree of elevation and the overall medical circumstances. Further tests may be done to determine more precisely the extent of damage. Besides follow-up tests, it should be emphasized that if a particular chemical substance, whether work-related or not, is causing the abnormality in the liver or a kidney function tests, exposure should be stopped to prevent further damage to these organs. Workers also need to minimize exposure to workplace liver and/or kidney toxins if they have kidney or liver disease of any origin.
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