Liver function tests 211923 221822216 2008-06-26T07:14:41Z 207.13.167.2 /* Lactate dehydrogenase (LDH) */ '''Liver function tests''' (LFTs or LFs), which include '''liver enzymes''', are groups of [[clinical biochemistry]] laboratory blood assays designed to give information about the state of a patient's [[liver]]. Most [[liver disease]]s cause only mild symptoms initially, but it is vital that these diseases be detected early. Hepatic (liver) involvement in some diseases can be of crucial importance. This testing is performed by a [[medical technologist]] on a patient's serum or [[Blood plasma|plasma]] sample obtained by [[Venipuncture|phlebotomy]]. Some tests are associated with functionality (eg. albumin); some with cellular integrity (eg. [[transaminase]]) and some with conditions linked to the biliary tract ([[gamma-glutamyl transferase]] and [[alkaline phosphatase]]). '''LIVER ENZYMES''' - Albumin (Alb) Albumin is a protein made specifically by the liver, and can be measured cheaply and easily. It is the main constituent of total protein; the remaining fraction is called globulin (including the immunoglobulins). Albumin levels are decreased in chronic liver disease, such as cirrhosis. It is also decreased in nephrotic syndrome, where it is lost through the urine. Poor nutrition or states of protein catabolism may also lead to hypoalbuminaemia. The half-life of albumin is approximately 20 days. Albumin is not considered to be an especially useful marker of liver synthetic function; coagulation factors (see below) are much more sensitive. 3.9 to 5.0 g/dL [1] -Alanine transaminase (ALT) || [[Alanine transaminase]] (ALT), also called Serum Glutamic Pyruvate [[Transaminase]] (SGPT) or Alanine aminotransferase (ALAT) is an [[enzyme]] present in [[hepatocyte]]s (liver cells). When a cell is damaged, it leaks this enzyme into the blood, where it is measured. ALT rises dramatically in acute liver damage, such as [[viral hepatitis]] or [[Paracetamol#toxicity|paracetamol (acetaminophen) overdose]]. Elevations are often measured in multiples of the upper limit of normal (ULN). -Aspartate transaminase (AST) [[Aspartate transaminase]] (AST) also called Serum Glutamic Oxaloacetic Transaminase (SGOT) or aspartate aminotransferase (ASAT) is similar to ALT in that it is another enzyme associated with liver parenchymal cells. It is raised in acute liver damage, but is also present in red cells, and cardiac and skeletal muscle and is therefore not specific to the liver. The ratio of AST to ALT is sometimes useful in differentiating between causes of liver damage. || 10 to 40 IU/L -Alkaline phosphatase (ALP) || [[Alkaline phosphatase]] (ALP) is an enzyme in the cells lining the [[biliary tract|biliary ducts]] of the liver. ALP levels in plasma will rise with large bile duct obstruction, intrahepatic [[cholestasis]] or infiltrative diseases of the liver. ALP is also present in [[bone]] and [[placenta]]l tissue, so it is higher in growing children (as their bones are being remodelled) and elderly patients with [[Paget's_disease_of_bone|Paget's disease]]. || 30 to 120 IU/L -Total bilirubin (TBIL) || [[Bilirubin]] is a breakdown product of [[heme]] (a part of [[haemoglobin]] in red blood cells). The liver is responsible for clearing the blood of bilirubin. It does this by the following mechanism: bilirubin is taken up into [[hepatocytes]], ''conjugated'' (modified to make it water-soluble), and secreted into the [[bile (biology)|bile]], which is excreted into the intestine. Increased total bilirubin causes jaundice, and can signal a number of problems: * 1. '''Prehepatic''': Increased bilirubin ''production''. This can be due to a number of causes, including hemolytic anemias and internal hemorrhage. * 2. '''Hepatic''': Problems with the liver, which are reflected as deficiencies in bilirubin ''metabolism'' (e.g. reduced hepatocyte uptake, impaired conjugation of bilirubin, and reduced hepatocyte secretion of bilirubin). Some examples would be cirrhosis and viral hepatitis. * 3. '''Posthepatic''': Obstruction of the bile ducts, reflected as deficiencies in bilirubin ''excretion''. (Obstruction can be located either within the liver or [[Bile duct|outside the liver]].) | 2 - 14 μmol/L -Direct bilirubin || The diagnosis is narrowed down further by looking at the levels of direct bilirubin. * If direct (i.e. conjugated) bilirubin is normal, then the problem is an excess of unconjugated bilirubin, and the location of the problem is upstream of bilirubin excretion. Hemolysis, viral hepatitis, or cirrhosis can be suspected. * If direct bilirubin is elevated, then the liver is conjugating bilirubin normally, but is not able to excrete it. [[Bile duct]] obstruction by gallstones or cancer should be suspected. | 0 - 4 μmol/L -Gamma glutamyl transpeptidase (GGT) || Although reasonably specific to the liver and a more sensitive marker for cholestatic damage than ALP, [[Gamma glutamyl transpeptidase]] (GGT) may be elevated with even minor, sub-clinical levels of liver dysfunction. It can also be helpful in identifying the cause of an isolated elevation in ALP. GGT is raised in alcohol toxicity (acute and chronic). In some laboratories, GGT is not part of the standard LFTs and must be specifically requested. || 0 to 51 IU/L ==Other tests commonly requested alongside LFTs:== ===5' nucleotidase (5'NTD)=== 5' [[nucleotidase]] is another test specific for cholestasis or damage to the intra or extrahepatic biliary system, and in some laboratories, is used as a substitute for GGT for ascertaining whether an elevated ALP is of biliary or extra-biliary origin. ===Coagulation tests (e.g. INR)=== The liver is responsible for the production of [[coagulation]] factors. The [[international normalized ratio]] (INR) measures the speed of a particular pathway of coagulation, comparing it to normal. If the INR is increased, it means it is taking longer than usual for blood to clot. The INR will only be increased if the liver is so damaged that synthesis of [[vitamin K]]-dependent coagulation factors has been impaired: it is not a sensitive measure of liver function. It is very important to normalize the INR before operating on people with liver problems (usually by transfusion with blood plasma containing the deficient factors) as they could bleed excessively. ===Serum [[glucose]] (BG, Glu)=== The liver's ability to produce glucose ([[gluconeogenesis]]) is usually the last function to be lost in the setting of fulminant liver failure. ===Lactate dehydrogenase (LDH)=== [[Lactate dehydrogenase]] is an enzyme found in many body tissues, including the liver. Elevated levels of LDH may indicate liver damage. ==External links== * [http://www.elevatedliverenzymes.net Elevated liver enzymes] * {{MeshName|Liver+function+tests}} * [http://www.mayoclinic.com/health/liver-function-tests/AN00876 Overview] at [[Mayo Clinic]] [[Category:Blood tests]] [[Category:Chemical pathology]] [[Category:Gastroenterology]] [[Category:Hepatology]] [[pt:Testes de função hepática]]