Establishing a diagnosis often involves bringing together information from several different sources. Any one source is often not enough to make a definitive diagnosis. Alkaline phosphatase is a marker for several conditions -- some normal, some associated with disease. An elevated alkaline phosphatase alone does not establish a particular disease, or even necessarily the presence of disease. It's used along with a medical history, physical exam, other laboratory work and possibly imaging to help make the diagnosis. Diagnosis and treatment of disease should be done with consultation of a health care professional.
Function and Sources
Alkaline phosphatase is an enzyme, which means that it's a protein that facilitates and speeds up chemical reactions in the body. This enzyme removes chemical groups called phosphates from molecules. It's found in all tissues of the body but is particularly concentrated in bone, liver, bile ducts, kidney and placenta. There are three slightly different versions of the protein: one in the GI tract, one in the placenta and one for all other tissues, says "Harrison's Principles of Internal Medicine" and "Robbins and Cotran Pathologic Basis of Disease."
Bone Diseases
Certain bone diseases, especially those associated with the formation of bone, can elevate alkaline phosphatase. The enzyme is expressed strongly by cells in the bone called osteoblasts that form new bone. Paget's disease is one example in which abnormal excessive bone formation leads to elevated alkaline phospatase. In addtion, cancer that metastasizes to bones, especially prostate, elevates the enzyme. Fractures and other bone disorders may also elevate alkaline phosphatase, according to "Harrison's Principles of Internal Medicine" and "Robbins and Cotran Pathologic Basis of Disease."
Liver Diseases
Liver and bile duct disorders can also elevate alkaline phosphatase. The bile ducts drain bile from the liver to the small intestine. A process that blocks or damages the bile ducts, such as a gallstone lodged in a main bile duct, can cause bile to back up and damage parts of the ducts and liver, releasing the enzyme from liver and bile duct cells into the blood. Other sources of damage can release the enzymes as well, such as certain drugs or cancer, according to the expert manuals mentioned earlier.
Blood Disorders
Certain conditions in the blood may also elevate alkaline phosphatase. Myelofibrosis occurs when the normal bone marrow is replaced with scar tissue, and can decrease and damage blood cells that are made in the marrow; it also leads to increased alkaline phosphatase. Polycythemia vera is a disorder in which bone marrow overproduces red blood cells, and increases levels of alkaline phosphatase. Infections can increase it, too.
Other Conditions
Elevated alkaline phosphatase is also found in children, pregnant women, and those taking contraceptive medications. There is also a condition called transient hyperphosphatasaemia of infancy, whic is a short-lived reaction to infection. Certain syndromes such as hyperphosphatasia with mental retardation syndrome can also elevate alkaline phosphatase, as can a type of cancer known as a seminoma, according to "Harrison's Principles of Internal Medicine" and "Robbins and Cotran Pathologic Basis of Disease."
References
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci et al; 17th Ed 2008
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar et al; 8th Ed 2009
