Liver Function Tests (LFTs): A Guide to Understanding Liver Health

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Introduction

The liver is one of the most important organs in the human body. It performs hundreds of essential functions, including processing nutrients, producing proteins, breaking down medications, regulating metabolism, storing vitamins, and removing harmful substances from the bloodstream. Because the liver is involved in so many physiological processes, diseases affecting this organ can have widespread effects on the body.

Liver Function Tests (LFTs) are a group of blood tests used to evaluate liver health, detect possible liver injury, assess bile flow, and investigate conditions that may affect the liver. These tests are frequently requested during routine medical checkups, investigations of unexplained symptoms, monitoring of medication effects, and follow-up of patients with known liver disease.

Despite their name, liver function tests do not measure liver function alone. Some tests primarily indicate injury to liver cells, while others assess the liver's ability to produce essential proteins or provide information about the flow of bile. Interpreting the results correctly requires understanding the purpose of each test, the pattern of abnormalities, the patient's symptoms, medical history, and sometimes additional investigations.

This comprehensive guide explains liver function tests in detail, including their components, normal reference ranges, clinical significance, causes of abnormal results, diagnostic interpretation, preparation, treatment considerations, and frequently asked questions.

1. What Are Liver Function Tests?

Liver Function Tests, commonly abbreviated as LFTs, are blood investigations used to evaluate different aspects of liver health.

An LFT panel commonly includes:

• Alanine aminotransferase (ALT).
• Aspartate aminotransferase (AST).
• Alkaline phosphatase (ALP).
• Gamma-glutamyl transferase (GGT).
• Total bilirubin.
• Direct bilirubin.
• Albumin.
• Total protein.

Some laboratories also report the globulin level, albumin-to-globulin ratio, or prothrombin time and international normalized ratio (PT/INR), depending on the requested panel.

Not every laboratory includes all these tests in its standard LFT panel. PT/INR is particularly important when assessing the liver's ability to produce clotting factors, but it may be ordered separately.

LFTs help clinicians identify patterns that may suggest liver inflammation, damage to liver cells, impaired bile flow, reduced protein production, or other disorders.

However, an abnormal LFT does not automatically mean that a person has serious liver disease. Likewise, normal results do not completely exclude liver disease. Some conditions, including early-stage fatty liver disease and certain chronic liver disorders, may occur with normal or only mildly abnormal enzyme levels.

2. Understanding the Liver and Its Functions

To understand LFT results, it is useful to understand what the liver normally does.

The liver is located primarily in the upper-right portion of the abdomen, beneath the diaphragm. It receives blood from the hepatic artery and the portal vein. The portal vein carries nutrient-rich blood from the digestive tract to the liver, allowing nutrients and many absorbed substances to be processed before entering the general circulation.

The liver performs several essential functions.

A. Metabolism of carbohydrates

The liver helps maintain normal blood glucose levels.

After a meal, excess glucose can be stored as glycogen. Between meals, the liver breaks down glycogen and produces glucose when necessary. This process helps supply energy to the brain and other tissues.

Severe liver dysfunction can interfere with glucose regulation, although blood glucose abnormalities have many other possible causes.

B. Metabolism of proteins

The liver processes amino acids and converts ammonia, a potentially toxic waste product of protein metabolism, into urea.

Urea is transported to the kidneys and removed through urine. When advanced liver disease impairs this process, ammonia may accumulate and contribute to hepatic encephalopathy in susceptible patients.

C. Production of plasma proteins

The liver produces albumin and many proteins involved in blood clotting.

Albumin helps maintain oncotic pressure, which keeps fluid within blood vessels, and transports substances such as hormones, fatty acids, and certain medications.

Reduced albumin production can occur in advanced liver disease, although low albumin also has nonhepatic causes, including malnutrition, inflammation, and protein loss through the kidneys or gastrointestinal tract.

D. Production and secretion of bile

The liver produces bile, which helps the body digest and absorb dietary fats.

Bile also provides a route for eliminating bilirubin, cholesterol, and certain waste products. Bile flows through the bile ducts toward the gallbladder and small intestine.

Conditions that obstruct or impair bile flow can cause elevations in ALP, GGT, and bilirubin.

E. Detoxification and drug metabolism

The liver modifies and helps eliminate many medications, alcohol, and other substances.

Certain drugs can injure liver cells, interfere with bile flow, or affect other liver processes. For this reason, LFTs may be monitored during treatment with medicines known to carry a risk of liver injury.

F. Storage of vitamins and minerals

The liver stores several nutrients, including vitamin B12, iron, and certain fat-soluble vitamins.

Liver disease can affect nutrient storage and metabolism, particularly when the disease is advanced.

G. Bilirubin processing

The liver takes up bilirubin from the blood, chemically conjugates it, and excretes it into bile.

Disruption of this process may increase bilirubin levels and cause jaundice, a yellow discoloration of the skin and the whites of the eyes.

Because the liver performs so many functions, no single blood test can completely describe its health.

3. Why Are Liver Function Tests Ordered?

Doctors may request LFTs for many reasons.

A. Investigation of symptoms

LFTs may be requested when a patient experiences symptoms that could indicate liver or biliary disease, such as:

• Yellowing of the eyes or skin.
• Dark-colored urine.
• Pale or clay-colored stools.
• Persistent itching.
• Unexplained fatigue.
• Nausea or vomiting.
• Reduced appetite.
• Discomfort in the upper-right abdomen.
• Abdominal swelling.
• Unexplained bruising or bleeding.

These symptoms are not specific to liver disease, so additional evaluation may be required.

B. Routine medical screening

LFTs may be included in a health assessment, particularly when a person has risk factors for liver disease.

Examples include obesity, type 2 diabetes, significant alcohol exposure, certain medication use, or possible exposure to viral hepatitis.

Routine testing should be guided by individual risk and clinical circumstances rather than assuming everyone requires the same testing schedule.

C. Monitoring known liver disease

Patients with conditions such as hepatitis, metabolic dysfunction-associated steatotic liver disease, cirrhosis, or autoimmune liver disease may need periodic blood tests.

The frequency depends on the diagnosis, disease severity, treatment, and changes in the patient's clinical condition.

D. Monitoring medications

Some medicines can cause liver injury. Depending on the medication and individual risk, clinicians may check liver enzymes before treatment and repeat them during therapy.

Examples of medicines associated with possible liver-related adverse effects include certain antibiotics, antiepileptic medicines, tuberculosis treatments, and some cholesterol-lowering medications.

Patients should not stop prescribed medication solely because they are concerned about an LFT result. The prescribing clinician should determine whether the medication needs adjustment or discontinuation.

E. Investigation of abnormal imaging

An ultrasound, CT scan, or MRI may reveal fatty liver, bile duct dilatation, a liver lesion, or another abnormality.

LFTs can provide additional information, although normal results do not necessarily exclude a structural liver problem.

4. Alanine Aminotransferase (ALT)

Alanine aminotransferase, or ALT, is an enzyme found mainly in liver cells.

It participates in amino acid metabolism. When liver cells become injured, ALT may leak into the bloodstream, causing its measured level to rise.

ALT is often considered more liver-specific than AST because a greater proportion of ALT activity is associated with the liver.

Normal ALT range

The reference range varies by laboratory, testing method, age, sex, and other factors. Many adult laboratories use an approximate range of 7–56 units per liter (U/L), although some use lower upper limits.

The laboratory's own reference interval should be used when interpreting an individual result.

Causes of elevated ALT

ALT may increase in several conditions:

• Metabolic dysfunction-associated steatotic liver disease (MASLD), commonly called fatty liver disease.
• Viral hepatitis, including hepatitis A, B, and C.
• Alcohol-associated liver disease.
• Medication-induced liver injury.
• Autoimmune hepatitis.
• Reduced blood flow to the liver.
• Some inherited metabolic disorders.
• Certain infections and systemic illnesses.

ALT can also rise after strenuous exercise or in association with muscle injury, although AST is often more prominent in muscle-related conditions.

What does a high ALT mean?

A raised ALT suggests that liver-cell injury may be occurring, but it does not directly measure how well the liver is functioning.

The degree of elevation provides useful information, but it must be interpreted in context.

A mild elevation may be associated with fatty liver disease, medications, or chronic viral hepatitis. A marked elevation can occur with acute viral hepatitis, severe drug-induced injury, or ischemic liver injury, among other causes.

The height of ALT alone cannot determine the amount of permanent liver damage.

Isolated ALT elevation

If ALT is elevated while other tests remain normal, clinicians may review alcohol consumption, medication use, metabolic risk factors, recent exercise, and viral hepatitis risk.

Depending on the level and duration of elevation, repeat testing or additional investigations may be appropriate.

5. Aspartate Aminotransferase (AST)

Aspartate aminotransferase, or AST, is another enzyme involved in amino acid metabolism.

AST is found in the liver but also in skeletal muscles, heart muscle, red blood cells, kidneys, and other tissues.

Therefore, an elevated AST level does not necessarily indicate liver disease.

Normal AST range

Many adult laboratories use an approximate range of 10–40 U/L. However, reference intervals differ between laboratories.

Causes of elevated AST

AST may increase because of:

• Acute or chronic liver inflammation.
• Alcohol-associated liver disease.
• Fatty liver disease.
• Medication-related liver injury.
• Muscle injury.
• Intense physical exercise.
• Hemolysis of blood cells.
• Reduced blood supply to tissues.
• Certain cardiac or systemic conditions.

If AST is elevated disproportionately to ALT, clinicians may consider alcohol-associated liver disease, advanced fibrosis, or muscle injury, among other possibilities.

However, the AST-to-ALT ratio cannot independently establish a diagnosis.

AST-to-ALT ratio

The AST-to-ALT ratio compares the two enzyme values.

An AST-to-ALT ratio greater than 2 may support alcohol-associated liver disease in an appropriate clinical setting. Nevertheless, this pattern is not exclusive to alcohol-related injury and may occur in other conditions, including advanced liver fibrosis.

A ratio below 1 is frequently seen in many forms of fatty liver disease and viral hepatitis, but it is not diagnostic of any one condition.

The ratio should never be interpreted without considering the actual enzyme values, medical history, and other findings.

6. Alkaline Phosphatase (ALP)

Alkaline phosphatase is an enzyme found in several tissues, including the liver, bile ducts, bones, intestines, and placenta.

In liver-related conditions, ALP often increases when bile flow is impaired or when cells lining the bile ducts are affected.

Normal ALP range

A commonly used adult reference interval is approximately 40–130 U/L, but the range differs by laboratory and age.

ALP can be physiologically higher during childhood and adolescence because of bone growth. It can also rise during pregnancy, particularly later in pregnancy, because the placenta produces an ALP form.

Causes of elevated ALP

Possible causes include:

• Bile duct obstruction.
• Gallstones.
• Cholestasis.
• Primary biliary cholangitis.
• Primary sclerosing cholangitis.
• Certain liver tumors or infiltrative diseases.
• Bone growth.
• Bone fractures.
• Some bone disorders.
• Pregnancy.

An isolated ALP elevation does not automatically mean that the liver is responsible.

How can the source of ALP be identified?

GGT is often measured when ALP is elevated.

If ALP and GGT are both elevated, a hepatobiliary source becomes more likely. If ALP is high but GGT is normal, a bone-related source may be considered, although this pattern is not definitive.

Additional testing may include bone-specific ALP, calcium, phosphate, vitamin D, or imaging, depending on the clinical situation.

7. Gamma-Glutamyl Transferase (GGT)

Gamma-glutamyl transferase, commonly called GGT, is an enzyme associated with the liver and biliary system.

It helps transfer amino acid components across cell membranes and is used clinically as a marker that can support the interpretation of other liver-related tests.

Normal GGT range

Reference intervals vary substantially. Many adult laboratories use approximate upper limits in the range of 40–60 U/L, with differences according to sex and laboratory method.

The laboratory's reported range is the most appropriate reference for an individual result.

Causes of elevated GGT

GGT can increase in:

• Bile duct obstruction.
• Cholestatic liver disease.
• Alcohol-associated liver disease.
• Fatty liver disease.
• Medication-related enzyme induction.
• Certain forms of hepatitis.
• Some pancreatic and systemic disorders.

GGT may also rise with certain medicines even when substantial liver injury is not present.

Is GGT specific for liver disease?

No. GGT is sensitive in some clinical situations but is not highly specific.

For example, a raised GGT can be associated with alcohol exposure, obesity, diabetes, and certain medications. An isolated increase does not prove alcohol misuse or establish a particular liver diagnosis.

GGT is most useful when interpreted alongside ALP, ALT, AST, bilirubin, and the patient's clinical history.

8. Bilirubin: Total, Direct, and Indirect

Bilirubin is a yellow pigment produced mainly during the breakdown of aging red blood cells.

Hemoglobin from red blood cells is broken down, producing substances that are ultimately converted into bilirubin. The liver processes this bilirubin so that it can be excreted in bile.

When bilirubin accumulates in the bloodstream, jaundice may develop.

A. Total bilirubin

Total bilirubin represents the combined amount of conjugated and unconjugated bilirubin measured in the blood.

A commonly used adult reference range is approximately 0.2–1.2 mg/dL, although laboratories differ.

An elevated total bilirubin level may occur because of increased bilirubin production, impaired liver uptake or processing, liver-cell injury, or obstruction of bile flow.

B. Direct bilirubin

Direct bilirubin largely represents conjugated bilirubin.

After bilirubin enters liver cells, it is conjugated with glucuronic acid, making it more water-soluble and allowing it to be excreted into bile.

Direct bilirubin may increase in conditions such as:

• Bile duct obstruction.
• Cholestasis.
• Hepatitis affecting bilirubin excretion.
• Certain inherited disorders of bilirubin transport.

C. Indirect bilirubin

Indirect bilirubin is generally estimated by subtracting direct bilirubin from total bilirubin.

It largely represents unconjugated bilirubin, which circulates bound to albumin before being processed by the liver.

Indirect bilirubin may rise because of:

• Increased red blood cell breakdown, known as hemolysis.
• Certain inherited conditions, including Gilbert syndrome.
• Ineffective production of red blood cells in some disorders.
• Reduced hepatic uptake or conjugation of bilirubin.

D. What is jaundice?

Jaundice is a yellow discoloration of the skin, mucous membranes, and whites of the eyes caused by increased bilirubin.

It may occur in liver disease, bile duct obstruction, hemolytic disorders, and other conditions.

Jaundice is a clinical sign, not a diagnosis. New jaundice in an adult requires prompt medical assessment, particularly when accompanied by abdominal pain, fever, vomiting, confusion, or bleeding.

E. Why does urine become dark?

Conjugated bilirubin is water-soluble and may enter the urine when its concentration in the blood increases.

This can make urine dark brown or tea-colored. Pale stools may occur when insufficient bile pigment reaches the intestine.

However, dark urine and pale stools have other possible causes and should be interpreted with the overall clinical picture.

9. Albumin: A Marker of Protein Production

Albumin is the most abundant protein in blood plasma. It is produced by the liver and has several important functions.

It helps maintain fluid within blood vessels and transports substances such as hormones, fatty acids, bilirubin, and many medications.

Normal albumin range

A common adult reference interval is approximately 3.5–5.0 grams per deciliter (g/dL), depending on the laboratory.

Causes of low albumin

Low albumin may be associated with:

• Advanced chronic liver disease.
• Poor nutritional intake or malnutrition.
• Chronic inflammation.
• Kidney disease causing albumin loss.
• Protein-losing gastrointestinal disorders.
• Severe illness.
• Significant burns or fluid-related changes.

Low albumin is not specific to liver disease.

What does low albumin indicate in liver disease?

Albumin has a relatively long half-life, around three weeks. Consequently, it may remain normal during early or acute liver injury.

A persistently low albumin level may support the presence of chronic or advanced liver dysfunction, particularly when accompanied by other clinical findings.

In chronic liver disease, low albumin may contribute to swelling of the legs and fluid accumulation in the abdomen. However, these findings can also result from heart disease, kidney disease, and other conditions.

10. Total Protein and the Albumin-to-Globulin Ratio

Total protein measures the combined concentration of albumin and globulins in the blood.

Globulins include several groups of proteins, including immunoglobulins, which are important components of the immune system.

Normal total protein

Many adult laboratories use an approximate reference interval of 6.0–8.3 g/dL.

Causes of abnormal total protein

Low total protein may occur with malnutrition, reduced protein production, kidney protein loss, or gastrointestinal protein loss.

High total protein may occur with dehydration, chronic inflammation, or increased immunoglobulin production.

Albumin-to-globulin ratio

The albumin-to-globulin ratio, or A/G ratio, compares albumin with globulin.

A low ratio may occur when albumin decreases, globulins increase, or both occur together. This can be seen in certain chronic inflammatory disorders, autoimmune conditions, and liver diseases.

A high ratio may occur when globulin levels are reduced or in other specific circumstances.

The ratio is a supportive finding rather than a stand-alone diagnostic test.

11. Prothrombin Time (PT) and International Normalized Ratio (INR)

Although PT/INR is not included in every standard LFT panel, it is an important investigation when assessing the liver's ability to produce clotting factors.

The liver synthesizes many proteins required for normal blood clotting. When the liver's synthetic capacity is severely impaired, PT may become prolonged and INR may increase.

What is PT?

Prothrombin time measures how long blood takes to clot through a specific laboratory pathway.

The result is usually reported in seconds.

What is INR?

The international normalized ratio standardizes PT results to improve comparison between laboratories.

In a person not taking anticoagulant medication, INR is commonly around 0.8–1.2, although the reference range varies.

Causes of prolonged PT/INR

Possible causes include:

• Severe liver dysfunction.
• Vitamin K deficiency.
• Certain anticoagulant medicines.
• Some clotting-factor disorders.
• Disseminated intravascular coagulation and other serious conditions.

A prolonged INR does not automatically mean that the liver is the cause.

Why is INR important in acute liver injury?

In a patient with acute liver injury, a rising INR can indicate worsening synthetic dysfunction.

When acute liver injury is accompanied by confusion or altered mental status, urgent assessment is essential because acute liver failure may be developing.

INR must be interpreted in the context of anticoagulant use, vitamin K status, and the patient's clinical condition.

12. What Is the Difference Between Liver Enzymes and Liver Function?

This is one of the most important concepts in interpreting LFTs.

Liver enzymes, including ALT and AST, mainly provide information about cell injury. ALP and GGT can provide clues about bile flow and biliary injury.

By contrast, albumin and PT/INR provide information about the liver's ability to synthesize important proteins, although both are affected by factors unrelated to the liver.

Bilirubin provides information about bilirubin production, processing, and excretion.

Therefore, a patient can have very high liver enzymes while still maintaining adequate synthetic function. Another patient with advanced chronic liver disease may have only mildly elevated enzymes but have low albumin, an increased INR, or other evidence of impaired liver function.

This distinction explains why the severity of liver disease cannot be judged from ALT or AST alone.

13. Understanding Common Patterns of Abnormal LFTs

Doctors do not interpret each test in isolation. Instead, they evaluate the pattern of abnormalities.

Three broad patterns are commonly recognized: hepatocellular, cholestatic, and mixed.

A. Hepatocellular pattern

A hepatocellular pattern occurs when ALT and AST rise more prominently than ALP.

Potential causes include:

• Viral hepatitis.
• Medication-induced liver injury.
• Autoimmune hepatitis.
• Fatty liver disease.
• Alcohol-associated liver disease.
• Ischemic liver injury.

The cause depends on the magnitude and timing of the elevation, associated symptoms, medication history, and other investigations.

B. Cholestatic pattern

A cholestatic pattern occurs when ALP rises more prominently than ALT and AST, often with an increase in GGT.

Possible causes include:

• Gallstones obstructing bile flow.
• Bile duct strictures.
• Primary biliary cholangitis.
• Primary sclerosing cholangitis.
• Medication-induced cholestasis.
• Certain infiltrative liver disorders.

Ultrasound is often an initial imaging investigation when bile duct obstruction is suspected.

C. Mixed pattern

A mixed pattern includes substantial elevations in both aminotransferases and ALP.

This may occur with certain medications, viral illnesses, autoimmune disorders, and biliary disease.

Additional investigation is usually required to identify the cause.

D. Isolated bilirubin elevation

When bilirubin is elevated but other liver tests are relatively normal, clinicians may consider Gilbert syndrome, hemolysis, or other disorders affecting bilirubin production or processing.

The direct and indirect bilirubin fractions help narrow the possibilities.

E. Isolated ALP elevation

An isolated ALP elevation may originate from bone, liver, placenta, or other sources.

GGT, clinical history, and sometimes additional laboratory testing can help establish the source.

14. The R Ratio in Drug-Induced Liver Injury

In clinical practice, specialists sometimes use the R ratio to classify suspected drug-induced liver injury.

The ratio compares the degree of ALT elevation with the degree of ALP elevation relative to their respective laboratory upper limits of normal.

The calculation is:

R ratio = (ALT ÷ ALT upper limit of normal) ÷ (ALP ÷ ALP upper limit of normal)

An R ratio of 5 or greater generally indicates a hepatocellular pattern, an R ratio of 2 or less indicates a cholestatic pattern, and a value between 2 and 5 indicates a mixed pattern.

This calculation is mainly used in the clinical evaluation of suspected drug-induced liver injury. It does not identify the specific cause and should not replace a full medical assessment.

15. Common Causes of Abnormal Liver Function Tests

Many different diseases and exposures can produce abnormal LFT results.

A. Fatty liver disease

Metabolic dysfunction-associated steatotic liver disease (MASLD) occurs when excess fat accumulates in the liver in association with metabolic risk factors.

Risk factors include:

• Obesity, particularly excess abdominal fat.
• Type 2 diabetes.
• Insulin resistance.
• Abnormal cholesterol or triglyceride levels.
• High blood pressure.
• Other metabolic abnormalities.

Some patients have simple steatosis, while others develop liver inflammation and progressive fibrosis. Advanced fibrosis can eventually lead to cirrhosis.

ALT and AST may be mildly elevated, but LFTs can also be normal despite the presence of fatty liver disease.

Diagnosis and risk assessment may require clinical evaluation, imaging, and noninvasive fibrosis assessment.

B. Viral hepatitis

Viral hepatitis occurs when a virus infects and inflames the liver.

Important types include hepatitis A, B, C, D, and E.

Hepatitis A and E are often transmitted through contaminated food or water, although transmission patterns vary. Hepatitis B is commonly transmitted through infected blood and body fluids, including during childbirth. Hepatitis C is primarily transmitted through blood exposure.

Acute viral hepatitis may produce marked ALT and AST elevations. Chronic hepatitis B or C may cause mild abnormalities or even normal enzyme levels for periods of time.

Specific blood tests are needed to identify the virus. LFTs alone cannot determine which type of viral hepatitis is present.

C. Alcohol-associated liver disease

Excessive alcohol exposure can cause liver fat accumulation, inflammation, fibrosis, and cirrhosis.

Some patients have elevated AST and ALT, and the AST-to-ALT ratio may exceed 2. GGT may also be elevated.

However, these patterns are not diagnostic on their own, and alcohol-associated liver disease may occur without dramatic enzyme abnormalities.

Reducing or avoiding alcohol is an important part of management when alcohol contributes to liver injury. Patients with possible alcohol dependence should seek medical advice before abruptly stopping, because withdrawal can be dangerous.

D. Drug-induced liver injury

Certain medications, herbal products, and dietary supplements can cause liver injury.

The pattern may be hepatocellular, cholestatic, or mixed. Symptoms may include fatigue, nausea, itching, dark urine, or jaundice, but some cases are detected only through blood testing.

Acetaminophen, also called paracetamol, can cause severe liver injury when taken in excessive amounts. The risk may be increased by taking multiple products that contain the same ingredient.

Suspected overdose requires immediate emergency assessment, even if the person initially feels well.

E. Gallstones and bile duct obstruction

Gallstones may remain in the gallbladder without causing symptoms. If a stone obstructs the common bile duct, bilirubin and cholestatic enzymes may increase.

Patients may experience upper abdominal pain, jaundice, dark urine, pale stools, or itching.

Fever and abdominal pain with jaundice can indicate acute cholangitis, a potentially life-threatening infection requiring urgent treatment.

F. Autoimmune hepatitis

Autoimmune hepatitis develops when the immune system attacks liver tissue.

It can cause elevated ALT and AST, fatigue, jaundice, and other symptoms. Some patients have few symptoms initially.

Diagnosis may involve immunoglobulin levels, autoantibodies, exclusion of other causes, and sometimes a liver biopsy.

Treatment often involves medicines that suppress inappropriate immune activity under specialist supervision.

G. Primary biliary cholangitis

Primary biliary cholangitis is a chronic autoimmune disease that damages small bile ducts within the liver.

It commonly produces a cholestatic pattern, particularly elevated ALP. Symptoms may include fatigue and persistent itching.

Specific antibodies and other investigations help establish the diagnosis.

H. Primary sclerosing cholangitis

Primary sclerosing cholangitis is a chronic disorder characterized by inflammation and scarring of bile ducts.

It can cause cholestatic LFT abnormalities and may be associated with inflammatory bowel disease, particularly ulcerative colitis.

Imaging of the bile ducts, often using magnetic resonance cholangiopancreatography, may be required.

I. Cirrhosis

Cirrhosis is advanced liver scarring that alters normal liver architecture and may impair blood flow through the liver.

Causes include chronic viral hepatitis, alcohol-associated liver disease, MASLD-related liver injury, autoimmune disease, and inherited conditions.

Patients may have normal or mildly abnormal aminotransferases despite significant disease.

Low albumin, elevated bilirubin, prolonged INR, low platelet counts, abdominal fluid accumulation, or other findings may provide evidence of advanced disease.

J. Reduced blood flow to the liver

Severe hypotension, shock, or certain cardiac conditions can reduce blood supply to the liver.

This may cause a rapid and marked rise in ALT and AST, sometimes referred to as ischemic hepatitis.

Management focuses on treating the underlying cause and supporting the patient's circulation.

K. Other causes

Abnormal LFTs may also occur in conditions such as hemochromatosis, Wilson disease, alpha-1 antitrypsin deficiency, celiac disease, thyroid disorders, muscle disease, and certain systemic infections.

This wide range of causes is why abnormal LFTs should be evaluated systematically rather than attributed to one disease without sufficient evidence.

16. Symptoms Associated With Liver Disease

Some people with liver disease have no symptoms, particularly during early stages.

When symptoms develop, they may include:

• Persistent fatigue.
• Reduced appetite.
• Nausea.
• Discomfort in the upper-right abdomen.
• Yellowing of the eyes or skin.
• Dark urine.
• Pale stools.
• Generalized itching.
• Swelling of the legs.
• Abdominal enlargement from fluid accumulation.
• Easy bruising or bleeding.
• Unintentional weight loss.
• Confusion or changes in alertness in advanced disease.

These symptoms can arise from multiple conditions, and their presence does not automatically confirm liver disease.

Nevertheless, jaundice, new abdominal swelling, confusion, vomiting blood, or black tarry stools warrant urgent medical assessment.

17. How Are Liver Function Tests Performed?

LFTs are generally performed using a blood sample collected from a vein, usually in the arm.

A trained healthcare professional cleans the skin, inserts a needle into a vein, and collects blood into one or more tubes.

The sample is sent to a laboratory, where instruments measure the requested analytes.

The procedure usually takes only a few minutes. Mild discomfort or bruising may occur at the needle site.

Is fasting required?

Fasting is not always required for an LFT panel alone.

However, a clinician may request fasting if the LFTs are being performed alongside other tests, such as certain glucose or lipid investigations, or if a particular laboratory protocol requires it.

Patients should follow the instructions given by their healthcare provider or laboratory rather than fasting unnecessarily.

Should medications be stopped before testing?

Patients should not stop prescribed medications without medical advice.

It is helpful to tell the clinician about all prescription medicines, over-the-counter products, herbal remedies, vitamins, and supplements being taken.

Recent alcohol exposure, strenuous exercise, acute illness, and other factors may also affect interpretation.

18. How to Interpret an LFT Report Step by Step

A structured approach helps avoid common interpretation errors.

Step 1: Review the laboratory reference ranges

Different laboratories use different reference intervals. Compare each result with the range printed on the report.

A value slightly outside the reference range does not always indicate disease, while a result within the range does not rule out every liver condition.

Step 2: Examine ALT and AST

Determine whether the aminotransferases are normal, mildly elevated, or markedly elevated.

Consider liver disease, medication exposure, alcohol, muscle injury, recent illness, and other relevant factors.

Step 3: Examine ALP and GGT

If ALP is elevated, GGT may help determine whether a liver or biliary source is likely.

An increase in both tests can suggest cholestasis or bile duct disease, although further evaluation may be necessary.

Step 4: Review bilirubin

Determine whether total bilirubin is elevated and, when available, whether the direct or indirect fraction predominates.

This can help distinguish impaired bile excretion from increased bilirubin production or reduced conjugation.

Step 5: Assess albumin and PT/INR

These tests provide information about synthetic function, but their results can be affected by nutrition, inflammation, vitamin K deficiency, anticoagulant medication, and other conditions.

Step 6: Consider the clinical picture

Age, symptoms, medical history, pregnancy status, medication exposure, alcohol use, metabolic risk factors, and previous test results all matter.

Step 7: Decide whether further testing is needed

Depending on the pattern, a clinician may request repeat LFTs, hepatitis testing, autoimmune markers, iron studies, ultrasound, elastography, or other investigations.

Persistent or unexplained abnormalities may require specialist assessment.