Liver Function Tests (LFTs)

Vocabulary flashcards covering markers, metabolic functions, classifications, normal ranges, and clinical implications of Liver Function Tests (LFTs).

Liver Function Tests (LFTs)

Noninvasive methods for screening liver dysfunction, identifying general types of disorders, assessing severity, predicting outcome, and following up on disease and treatment.

Steatosis

A condition referring to fatty liver.

Hemochromatosis

A genetic disorder characterized by excessive iron storage.

Group I LFTs

Markers of liver dysfunction, including serum bilirubin (total and conjugated), urine bile salts and urobilinogen, total protein, serum albumin, albumin/globulin ratio, and prothrombin time.

Group II LFTs

Markers of hepatocellular injury, consisting of Alanine aminotransferase (ALT) and Aspartate aminotransferase (AST).

Group III LFTs

Markers of cholestasis, consisting of Alkaline phosphatase (ALP) and $\gamma$-glutamyltransferase (GGT).

Bilirubin

A byproduct of red blood cell breakdown and the yellowish pigment observed in jaundice.

Normal Serum Bilirubin Level

$$0.2 - 0.8\,mg/dL$$

Unconjugated (Indirect) Bilirubin Normal Range

$$0.2 - 0.7\,mg/dL$$

Conjugated (Direct) Bilirubin Normal Range

$$0.1 - 0.4\,mg/dL$$

Latent Jaundice Bilirubin Threshold

Serum bilirubin level above $1\,mg/dL$.

Jaundice Bilirubin Threshold

Serum bilirubin level above $2\,mg/dL$.

Pre-hepatic (Hemolytic) Jaundice

Jaundice caused by abnormal red cells, antibodies, drugs and toxins, thalassemia, hemoglobinopathies, Gilbert's syndrome, or Crigler-Najjar syndrome.

Hepatic (Hepatocellular) Jaundice

Jaundice caused by viral hepatitis, toxic hepatitis, or intrahepatic cholestasis.

Post-hepatic Jaundice

Jaundice caused by extrahepatic cholestasis, gallstones, tumors of the bile duct, or carcinoma of the pancreas.

Stercobilin

The brown pigment formed by bacterial oxidation of urobilinogen in the intestine, excreted in feces.

Urobilin

The yellow pigment converted from urobilinogen in the kidney that gives urine its characteristic color.

Urobilinogen (UBG) Normal Excretion

A fraction of urobilinogen excreted in urine, which is less than $4\,mg/day$.

Serum Albumin

The most abundant protein synthesized by the liver, with normal serum levels of $3.5 - 5\,g/dL$ and a half-life of $20\,\text{days}$.

Serum Globulin

Proteins with normal levels of $2.5 - 3.5\,g/dL$, composed of $\alpha$- and $\beta$-globulins synthesized by the liver, and immunoglobulins (IgG elevated in autoimmune hepatitis, IgA elevated in alcoholic liver disease).

Albumin to Globulin (A/G) Ratio

The normal ratio of serum albumin to globulin, which is $1.2/1 - 1.5/1$.

Prothrombin Time (PT)

A test measuring prothrombin (half-life of $6\,\text{hrs}$) to assess liver synthetic function; it becomes prolonged only when the liver loses more than $80\%$ of its reserve capacity.

Aspartate Aminotransferase (AST)

A marker of hepatocellular damage with a normal range of $8 - 20\,U/L$.

Alanine Aminotransferase (ALT)

A liver-specific marker of hepatocellular injury with a normal range of $13 - 35\,U/L$ in males and $10 - 30\,U/L$ in females.

Alkaline Phosphatase (ALP)

A non-specific marker of liver disease produced by bone osteoblasts and present on hepatocyte membranes, with a normal range of $40 - 125\,U/L$.

$\gamma$-glutamyltransferase (GGT)

An enzyme involved in glutathione synthesis with a normal range of $10 - 30\,U/L$; it is highly sensitive for detecting alcohol abuse.

Kupffer Cells

Specialized macrophages located in the liver that remove bacteria from portal blood, phagocytose damaged blood cells, and remove cellular debris.