Liver function tests (LFTs) help your doctor make some assumptions that there is a problem with the liver. But do not misunderstand about this test. While LFTs are often used to reflect a well-functioning liver condition, this test may be wrong because not all tests accurately assess all of the different functions of the liver. In fact, there are usually 3 major type of LFTs which are listed below
Bilirubin is a metabolic product of hemoglobin and heme-containing enzymes. 95% of bilirubin is produced by red blood cell degradation. Bilirubin consists of two components: Unconjugated bilirubin and Conjugated bilirubin. Unconjugated bilirubin, also known as indirect bilirubin, is fat-soluble, bound to plasma albumin and therefore not glomerular. When it comes to the liver, unconjugated bilirubin is conjugated with glucuronic acid to become Conjugated bilirubin. This bilirubin is also known as direct bilirubin, which is soluble in water and secreted into the bile secretions.
- Increased unconjugated bilirubin. Rarely due to liver disease, possibly due to increased production of bilirubin (hemolysis, ineffective erythropoiesis, reabsorption from hematoma) Bilirubin in hepatocytes (Gilbert’s syndrome) or reduction of bilirubin conjugation due to glucuronyl transferase deficiency (Crigler-Najjar syndrome).
- Increased conjugated bilirubin. is associated with hepatic disease, possibly due to reduced bilirubin secretion in the gallbladder or by cholestatic or extrahepatic bile duct. Clinically, it is often difficult to distinguish between cholestatic hepatitis (hepatitis, cirrhosis, primary liver cirrhosis) with extrahepatic biliary obstruction (cholelithiasis, gallbladder cancer, pancreatic cancer, Primary biliary atresia). Causes of cholestasis may be due to rare hereditary diseases (Dubin-Johnson syndrome, Rotor’s syndrome); Drugs and gallstone can also be risky factors. When bilirubin is elevated, a portion of bilirubin attaches to plasma albumin, which is not excreted in the urine. As a result, jaundice usually decreases more slowly after the cause of the bile has been resolved. The rest of the bilirubin, which is not attached to albumin, is excreted in the urine, limiting hyperbilirubinemia.
- Increased total Bilirubin is usually due to a combination of mechanisms (hemolytic co-morbidities in the liver that lead to bile clogging)
Liver is the only organ that synthesizes albumin for the body. Albumin maintains intraocular pressure in the arteries and is a carrier of substances in the blood, especially drugs. Due to the large storage capacity of the liver and the prolonged half-life of albumin (about 3 weeks), blood albumin levels are reduced only in chronic liver disease (cirrhosis) or when severe liver damage occurs. In patients with cirrhosis of the ascites, albumin levels decrease due to leakage into the epidermis.
Decreased serum albumin is also found in malnutrition or abnormal albuminuria (nephrotic syndrome) or gastrointestinal (chronic colitis) loss. In patients with dark jaundice, albumin may be artificially reduced due to elevated bilirubin, which may interfere with albumin determination.
The testing group assesses the curriculum status
AST (Aspartate aminotransferase) or SGOT (Serum Glutamic Oxaloacetic Transaminase)
Presence in cytoplasm and mitochondria of the cell. AST is present in myocardium and rhabilians more than in the liver. In addition, AST also exists in the kidneys, brain, pancreas, lung, leukocyte and red blood cells.
ALT (Alanine aminotransferase) or SGPT (Serum Glutamic Pyruvic Transaminase)
Presumably present in the hepatocellular cytoplasm, an increase in ALT is more sensitive and specific than AST in liver diseases.
In adults, concentrations of AST and ALT in men are higher than for women and also vary with age and weight. These enzymes are released into the bloodstream when cell membrane damage increases permeability. However, elevation of liver enzymes was not completely correlated with hepatic necroinflammation. The origin and mechanism of eliminating AST and ALT into the blood are mostly unknown. Transaminases increase in almost all liver diseases but are not completely specific for the liver because they increase in other diseases such as
- Myocardial infarction
- Myeloid injury (myocarditis, hypothyroidism)
Conversely, these enzymes can be artificially reduced with increased blood urea. AST elevation may occur in the case of macro-AST (AST attached to an immunoglobulin).
In general, LFTs are not the perfect marker to pinpoint the exact disease. Nonetheless, it warns the physicians that something is wrong with the liver. Further, it helps them determine the need for additional tests. And by combining these extra test results with LFTs, doctors will have a better evidence to diagnose whether the liver is diseased or not. By storing a series of LFTs results from previous months and years, in some cases both the physician and the patient can predict whether the liver condition is stable, has improved, has recovered or worse.
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Review Date: May 24, 2017 | Last Modified: May 24, 2017
WebMD, What is a Liver Function Test, http://www.webmd.com/hepatitis/hepc-guide/liver-function-test-lft#1. Accessed on April 5, 2017
Shivaraj Gowda,1 , & Prakash B. Desai, Vinayak V. Hull, 1 Avinash A K. Math, Sonal N. Vernekar, and Shruthi S. Kulkarni, A review on laboratory liver function tests. Accessed on April 5, 2017