Liver function tests

# Overview
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 diseases 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.

# General approach
- Patients with hepatocellular process, have higher elevations in the serum aminotransferases compared to alkaline phosphatase. However, patients with cholestatic process have the opposite lab findings.
- The elevated serum bilirubin is a non-specific finding and can be elevated in both hepatocellular and cholestatic conditions.
- The presence of bilirubin in the urine reflects direct hyperbilirubinemia and hepatobiliary disease.
- Unconjugated bilirubin is tightly bound to albumin and is not filtered by the glomerulus. Thus, presence of unconjugated bilirubin in urine suggest an underlying kidney disease.
- Conjugated bilirubin may be found in the urine when the total serum bilirubin concentration is normal. This is so, because the renal capacity for resorption of conjugated bilirubin is low. Additionally, the methods used can detect urinary bilirubin as low as 0.05 mg/dL. Thus, bilirubinuria can be an early sign of liver disease.
- A low albumin suggests a chronic process such as cirrhosis or cancer, while a normal albumin suggests a more acute process such as viral hepatitis or choledocholithiasis.
- Elevated Prothrombin time suggests either vitamin K deficiency, malabsorption of vitamin K or significant hepatocellular dysfunction. Failure in correction of prothrombin time with parenteral vitamin K indicates severe hepatocellular injury.
- Approach to mild (less than 4 times the upper limit of normal) chronic ( 6 months) elevation in aminotransferase:
Medications - Albendazole, Nonsteroidal anti-inflammatory drugs, acetaminophen, antibiotics, statins, antiepileptic drugs, and antituberculous drugs, herbal preparations and illicit drug. Drugs as a cause for elevation of aminotransferases can be suggested by: lack of symptoms and lab abnormalities prior to consumption of the drug, and improvement in these once the drug is withdrawn.
Alcoholism -  An AST to ALT ratio of 2:1 or greater is suggestive of alcohol abuse. Of note, a similar AST/ALT ratio can also be seen in nonalcoholic steatohepatitis, and hepatitis C with development of cirrhosis. A 2 fold elevation of the gamma glutamyltransferase (GGT) in patients whose AST to ALT ratio is greater than 2:1 strongly suggests alcohol abuse.
Assess for hepatitis B and C - The risk for Hepatitis B & C is increased in patients with history of IV drug use, transfusion, and in patients from parts of the world where a high disease prevalence exists (eg, Southeast Asia, and sub-Saharan Africa). The following tests should be ordered in patients with suspected Hepatitis B: Hepatitis B surface antigen (HBsAg), Hepatitis B surface antibody (HBsAb), Hepatitis B core antibody (HBcAb)
Assess for hemochromatosis, and fatty liver.
- Medications - Albendazole, Nonsteroidal anti-inflammatory drugs, acetaminophen, antibiotics, statins, antiepileptic drugs, and antituberculous drugs, herbal preparations and illicit drug. Drugs as a cause for elevation of aminotransferases can be suggested by: lack of symptoms and lab abnormalities prior to consumption of the drug, and improvement in these once the drug is withdrawn.
- Alcoholism -  An AST to ALT ratio of 2:1 or greater is suggestive of alcohol abuse. Of note, a similar AST/ALT ratio can also be seen in nonalcoholic steatohepatitis, and hepatitis C with development of cirrhosis. A 2 fold elevation of the gamma glutamyltransferase (GGT) in patients whose AST to ALT ratio is greater than 2:1 strongly suggests alcohol abuse.
- Assess for hepatitis B and C - The risk for Hepatitis B & C is increased in patients with history of IV drug use, transfusion, and in patients from parts of the world where a high disease prevalence exists (eg, Southeast Asia, and sub-Saharan Africa). The following tests should be ordered in patients with suspected Hepatitis B: Hepatitis B surface antigen (HBsAg), Hepatitis B surface antibody (HBsAb), Hepatitis B core antibody (HBcAb)
- Assess for hemochromatosis, and fatty liver.

# Standard liver panel

# 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 out.

## 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.