Alkaline Phosphatases are a group of enzymes found primarily the liver (isoenzyme ALP-1) and bone (isoenzyme ALP-2). There are also small amounts produced by cells lining the intestines (isoenzyme ALP-3), the placenta, and the kidney (in the proximal convoluted tubules). What is measured in the blood is the total amount of alkaline phosphatases released from these tissues into the blood. As the name implies, this enzyme works best at an alkaline pH (a pH of 10), and thus the enzyme itself is inactive in the blood. Alkaline phosphatases act by splitting off phosphorus (an acidic mineral) creating an alkaline pH.
The primary importance of measuring alkaline phosphatase is to check the possibility of bone disease or liver disease. Since the mucosal cells that line the bile system of the liver are the source of alkaline phosphatase, the free flow of bile through the liver and down into the biliary tract and gallbladder are responsible for maintaining the proper level of this enzyme in the blood. When the liver, bile ducts or gallbladder system are not functioning properly or are blocked, this enzyme is not excreted through the bile and alkaline phosphatase is released into the blood stream. Thus the serum alkaline phosphatase is a measure of the integrity of the hepatobiliary system and the flow of bile into the small intestine.
In addition to liver, bile duct, or gallbladder dysfunction, an elevated serum alkaline phosphatase can be due to rapid growth of bone since it is produced by bone-forming cells called osteoblasts. One would expect that growing children have higher levels than full-grown adults. The relationship of alkalinity to bone development warrants further discussion because it plays a major role in the prevention and reversal of osteoporosis. Just as calcium builds up around faucets, so is calcium laid down into bone. The reason the calcium deposits on your faucet is because the water is alkaline and calcium comes out of solution and crystallizes in an alkaline environment. The reverse is also true, “Lime -Away”, vinegar, or any other acidic solution dissolve the calcium deposits because they are acidic. It makes sense that osteoblasts by creating a local environment of alkalinity via alkaline phosphatase helps build bone. It also implies that in order to slow bone loss, one can not be in an acidic state. Studies have shown that giving bicarbonate of potassium is just as effective as calcium in correcting osteoporosis! One would expect then that in an acidic state, the body will compensate for this by increasing the bone alkaline phosphatase levels…
Because acid-alkaline is influenced by many other glands, the implications of serum alkaline phosphatase levels must consider more than just bone and liver function. Associated organs/glands include adrenals, uterus, prostate, and intestine.
The consequences of impaired bile flow are pervasive since bile is critical to your body’s ability to process fats. As a result, fats remain undigested in the digestive tract and can cause bloating, cramps, light colored stools, gaseousness, etc. especially after a rich food. Many patients report pressure or pain in the right upper area of their abdomen where the liver and gallbladder are located. You may have discomfort in the right shoulder or between your shoulder blades anywhere from your mid-back to the base of your neck. Many people say they “carry my stress in the upper back and neck.” This may due to gallbladder dysfunction. Unfortunately, a normal alkaline phosphatase does not exclude hepatobiliary dysfunction. In many cases, even the ultrasound shows no gallstones, etc. Rather the problem is that the bile does not flow freely throughout the system, which may result in insufficient bile action.
The consequences of impaired bile function involve the endocrine system in a major way because all of the steroid hormones are metabolized in part by the liver. These include the sex hormones (androgens and estrogens). As a result the menstrual cycle, sexual functions and sex characteristics can be affected.
The optimal range for alkaline phosphatase depends on your age. A growing adolescent will have a much higher alkaline phosphatase than a full grown adult because his/her osteoblasts are laying down bone very rapidly. For an adult, 50-75 mg/dl is considered a reasonable optimal range.
An increased serum Alkaline Phosphatase may be due to:
Congestion or obstruction of the biliary tract, which may occur within the liver, the ducts leading from the liver to the gallbladder, or the duct leading from the gallbladder through the pancreas that empty into the duodenum (small intestine). Any of these organs (liver, gallbladder, pancreas, or duodenum) may be involved.
*See the lab section on liver enzyme tests for more about causes of liver dysfunction.
An elevated alkaline phosphatase almost always requires other tests to determine the origin of the condition. For example, liver enzyme tests to check the integrity of the liver, x-rays or other bone images if a bone abnormality is evident. Although not used often, the isoenzyme profile of alkaline phosphatases can be determined to see if the elevation of alkaline phosphatase came primarily from liver (ALP-1), bone (ALP-2), or elsewhere. Most often, however there is a modest elevation from ideal but the actual value is within the laboratories reference range and the origin is inferred from the symptoms, exam, or existing lab results.
A decreased serum alkaline phosphatase may be due to: