Liver function tests (Liver Profile) and liver diseases.

Liver function tests (LFTs) are a group of blood tests used to evaluate the health of the liver. They measure the levels of proteins, enzymes, and other substances in the blood that are related to the liver. The tests can help diagnose and monitor a variety of liver diseases, including cirrhosis, hepatitis, and liver cancer.

LFTs measure the levels of two proteins, albumin and globulin, in the blood. Albumin is a protein produced by the liver that helps keep fluid in the bloodstream and transports vitamins, hormones, and other substances throughout the body. Globulin is a protein that helps the immune system fight infection. LFTs also measure the levels of enzymes that are released from the liver when it is damaged. These enzymes are called aspartate aminotransferase (AST) and alanine aminotransferase (ALT).

In addition to proteins and enzymes, LFTs also measure the level of bilirubin in the blood. Bilirubin is a yellowish pigment produced by the breakdown of red blood cells. High levels of bilirubin in the blood can indicate liver disease.

LFTs can also be used to measure the levels of other substances in the blood that are related to liver function. These include albumin/globulin ratio, alkaline phosphatase, gamma-glutamyl transpeptidase (GGT), cholesterol, and triglycerides.

LFTs are usually ordered when a person has symptoms of a liver disorder, such as jaundice, fatigue, abdominal pain, or loss of appetite. They can also be ordered to monitor the progress of a known liver condition or to screen for liver damage in people at risk, such as those with a history of alcohol abuse or viral hepatitis. Liver function tests can help diagnose and monitor a variety of liver diseases, and are an important part of a comprehensive diagnostic and treatment plan for any suspected or known liver disorder.  

Basis of liver function tests

Tests for AST and ALT assess the damage to liver tissue while Prothrombin time, activated partial thromboplastin time (aPTT), Albumin, and Bilirubin assess the synthetic function of the liver.

Damage to the liver tissue may increase levels of AST and ALT above the normal levels but are not specific for that since many other conditions could also alter their concentrations.

PT and APTT, which comes under coagulation studies, assess blood clotting ability. The liver synthesises many chemical factors involved in blood clotting; thus, an abnormality of clotting may indicate the liver's abnormal synthetic function. Delayed blood clotting times are associated with many other diseases and are not specific to liver diseases. 

Biochemical liver function tests rarely give a precise diagnosis on their own. Pathologies to which these tests are sensitive are also common for many other conditions. 

Liver function tests are inexpensive, widely available and non-invassive, making them necessary before going to deeper investigations.

More complex tests, imaging studies and liver biopsies follow up abnormal indications.

After prolonged usage of a specific drug, a physician may recommend a liver function test to asses any damage to the liver instead of going for more invasive liver biopsies.

Why does a liver function test is recommended?

• Assess the side effects of after a drug therapy.
• After a snake bite or any other poison ingestion.
• To assess the severity of cirrhosis (Liver fibrosis).
• To assess the extent of damage by alcoholic hepatitis and monitor the response to treatment.
• As a primary screening for liver infections.
  

Patient preparation for a liver function test.

Patients should always obtain medical guidance about the preparation because some drugs and foods may affect test reagents and change liver functions. 

Lipid profile indices:

ALT is an enzyme found in the liver cells. It is released to the blood when the liver is damaged. Increased ALT levels in blood are observed in liver infections, cirrhosis, tumors and when blood supply to the liver is reduced.

AST is an enzyme which is less specific than ALT for liver damage. It is also contained in heart and muscles. AST is present in blood in low levels and show an increase when muscle or liver damage occur. It may be a result of cirrhosis, hepatitis or any liver disease.

ALP is an enzyme found in the liver and bone and is less specific than ALT for liver disease. Rise of ALP may indicate liver damage, bone disease or an obstruction of bile duct.

Albumin is an blood protein synthesized by the liver. Low levels of albumin may result from decreased productive function of the liver. Decreased albumin level was observed in kidney diseases too.

Bilirubin originates from breakdown of red blood cells. It is conjugated in the liver to increase solubility. Upon conjugation bilirubin is secreted to the gut and it gives feces its yellowish color. When conjugation function of liver is decreased bilirubin gets accumulated in blood causing jaundice.

 

Most common liver diseases;

Hepatitis

Hepatitis is the inflammation of the liver resulting from injury or infection.
It may be acute, chronic, or a combination of both. Viral infections are the most common cause of hepatitis. Heavy alcohol usage, toxins, and other medications may also cause hepatitis.

Acute hepatitis

Acute hepatitis usually results from viral infections (particularly

with hepatitis viruses A, B, C, D and E, Epstein–Barr virus and cytomegalovirus). Overdosage of Paracetamol (acetaminophen) was also found to cause hepatitis. Standard liver function tests identify the typical underlying pathological process common to many clinical conditions.AST and ALT levels increase in the early stages. The rise of bilirubin concentrations is observed at the later stages. Increased bilirubin levels cause jaundice (Yellowing of skin, yellowish eyeballs) and discomfort. The appearance of bilirubin in urine when non-specific symptoms appear is vital in the presumptive diagnosis of hepatitis. Urobilinogen disappears when the jaundice progress. In a healthy human body, bilirubin is excreted (After conjugation as conjugated bilirubin) from blood to the gut through the liver. Within the gut, bilirubin is metabolized by bacteria to urobilinogen, which is absorbed and excreted by the kidney with urine. When the liver excretes no bilirubin, urobilinogen is not formed and disappears in urine.

Chronic hepatitis

Hepatitis persisting over six months is classified as chronic hepatitis. Infection with Hepatitis B or Hepatitis C virus, high alcohol usage or destruction of the liver tissue by immune responses (autoimmune hepatitis) leads to chronic hepatitis.

AST and ALT levels in the blood are usually elevated in chronic hepatitis, but other liver function tests remain normal unless cirrhosis develops. Untreated autoimmune hepatitis usually progresses to cirrhosis and is preventable with immunosuppressive treatment.

Cirrhosis 

Cirrhosis causes the liver's cells to die, which leads to fibrosis and scarring.

Cirrhosis can be brought on by drinking too much alcohol, contracting an infection, developing an autoimmune condition, or inheriting a metabolic disorder.Impaired hepatic function progress to liver failure.

Reference ranges liver profile test:

• Bilirubin – should be between 0.1 - 1.2 mg/dL

• Albumin – should be between 3.5 - 5.0 g/dL

 • ALT - should be between 7 - 55 U/L

 • AST – should be between 8 - 48 U/L

 • ALP – should be between 45 - 115 U/L

 • Total protein – should be between 6.3 - 7.9 g/dL

 • GGT – should be between 9 - 48 U/L

• PT - 11 -13.5 seconds (If blood thinning medications such as Warfarin are not used
• aPTT - 21- 35 second

Patients should take medical advice on any abnormal results and Always let your test report be interpreted by a qualified healthcare professional.