Orange or very dark urine may be caused by liver disease, and your doctor will probably begin your evaluation with a panel of blood tests known as liver function tests, or LFTs. The liver is the largest internal organ and performs a wide variety of functions that are essential to life. The diseases to which it is susceptible are equally varied and numerous. LFTs represent a small minority of the diagnostic tools available to your doctor. The pattern of results from those tests will suggest certain specific diseases and guide the next steps in your evaluation.
An LFT panel includes measurements of several substances in your bloodstream that may indicate liver disease. Chemicals typically measured include bilirubin and enzymes designated by the abbreviations AST, ALT, ALP and GGT. Other substances may also be measured to assess your overall liver health.
Abnormal Red Blood Cell Destruction
Bilirubin is produced from the breakdown of old red blood cells. It has a yellowish color and is normally processed through the liver and into the intestine. When diseases or drugs cause abnormally rapid destruction of red blood cells, the liver's capacity to handle bilirubin is overwhelmed and blood levels rise. Some of the excess bilirubin from the bloodstream is excreted in the urine, causing it to appear deep yellow or orange. An elevated blood bilirubin is usually the only component of the initial LFT panel that is abnormal when you have liver disease.
Liver Cell Destruction
Hepatitis due to viruses, alcohol, and drugs damages liver cells, as do a host of other diseases, such as shock and generalized infections of the bloodstream. Liver cells contain certain enzymes, especially those called aminotransferases. ALT and AST are aminotransferases present in high concentrations in liver cells. Liver cell damage causes leakage of these enzymes into the bloodstream. When your ALT and AST are elevated along with bilirubin, your doctor will perform additional tests to determine what type of liver damage you are experiencing.
Bile Duct Obstruction
Enzymes known as ALP and GGT are distributed throughout your body but are particularly concentrated in the cells that line the bile ducts. Blockage of these ducts -- due to gallstones, cancer or other diseases or injury -- damages the lining cells and increases bilirubin, ALP and GGT levels. When these substances are elevated, the next step in evaluating your condition is likely to be a special x-ray or another means of inspecting the bile ducts.
Mild LFT Elevation and Orange Urine
Despite the name, abnormal LFTs do not always indicate liver disease. One or another of the substances measured may be modestly increased in normal people. Your doctor will consider other causes of orange urine -- such as dehydration, medications and dyes -- if your LFTs are minimally abnormal.