Liver Function Tests
Liver is the versatile organ in which maximum metabolism & other biochemical functions are takes place.
The importance of liver function tests are –
- To assess the severity of liver damage.
- To differentiate different type of Jaundice.
- To find out the present of latent liver disease.
Major functions of the Liver
- Metabolic functions:
- Carbohydrate metabolism: Glycolysis, glycogen synthesis, breakdown, gluconeogenesis & HMP shunt.
- Lipid metabolism: Fatty acid synthesis, ketogenesis, cholesterol synthesis & excretion, bile acid synthesis, lipoprotein synthesis etc.
- Protein metabolism: Synthesis of plasma proteins, synthesis of urea, synthesis of some coagulation factors.
- Hormone synthesis: Metabolism & excretion of steroid hormones & metabolism of peptide hormones.
- Synthetic function :
Synthesis of plasma proteins, clotting factors, cholesterol, TAG & lipoproteins.
- Excretory function :
Excretion of bile pigments & bile salts into the bile.
- Detoxification :
Detoxification of ammonia, drugs & other xenobiotics & their excretion.
- Regulation of blood glucose : (Hepatic glycogenesis and gluconeogenesis).
- Storage function : Glycogen, Vitamins-A, D, K, B12 & Iron.
Classification of Liver function Tests
A. Biochemical classification
I. Tests based on liver excretory function
- Serum-bilirubin: Total, conjugated and unconjugated
- Urine: Bile pigments, bile salts and urobilinogen
- II. Liver enzymes
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
- Alkaline phosphatase (ALP)
- Gamma glutamyl transpeptidase (GGT)
III. Tests for synthetic function of liver
- Total proteins
- Serum albumin, globulins, A/G ratio
- Prothrombin time
- Special tests
- Ceruloplasmin
- Ferritin
- a-Fetoprotein
- Clinical classification
- Markers of liver dysfunction
- Serum bilirubin: Total, conjugated
- Urine: Bile pigments, bile salts and urobilinogen
- Total protein, serum albumin and A/G ratio
- Prothrombin time
- Blood ammonia
- Markers of hepatocellular injury
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
III. Markers of cholestasis (obstruction to the flow of bile)
- Alkaline phosphatase (ALP)
- Gamma glutamyl transpeptidase (GGT)
Tests based on Excretory functions of liver
Serum bilirubin
- Normal serum bilirubin level varies from 0.2 to 1.0 mg/dl. Of this, the unconjugated bilirubin (bilirubin–albumin complex) varies from 0.2 to 0.4 mg/dl and conjugated bilirubin varies from 0.2 to 0.6 mg/dl.
Van den bergh reaction
- Jaundice is the most common characteristic clinical manifestation occurring due to fluctuations in serum bilirubin.
- Principle: When serum bilirubin is treated with Van den berghs diazo reagent to form a purple red colored “azo bilirubin”. (Diazo reagent consist of sulfanilic acid in HCL and Sodium nitrite)
- Procedure: Take 0.3 ml of serum into each two test tubes, Add 0.3 ml of D.W. to one which serves as control and 0.3 ml of freshly prepared diazo reagent into second test. Mix both the tubes and observe.
- 1. If red or purple color develops within 30 seconds – Direct positive test, due to presence of conjugated bilirubin.
- 2. If color is not obtained, then add methanol & mix. Color develops (within 30 minutes) – Indirect positive test, due to presence of unconjugated billirubin.
- 3. Biphasic test: serum contains both D & I billirubin; Purple color produced immediately which is further intensified by methanol addition.
Tests for Bilirubin in urine:
- The presence of bilirubin in urine suggests the increased level of conjugated bilirubin in blood which is due to hepatic or obstructive jaundice.
- Van den Bergh’s test
- Gmelin’s test
- Cole’s test
- Fouchet’s test
- Ehrlich’s test
Bile salts:
- Bile salts are excreted along with bile pigments and these are detected by
- Hay’s sulphur powder test
- Pettenkoffer’s test
- Oliver’s test
- Bile salts are excreted in urine in Obstructive Jaundice and may be in hepatocellular Jaundice.
Test for Stercobilinogen and Stercobilin in feces:
- Normally 50-300 mgs of bile pigments are excreted daily in the feces.
- Increase of this value indicates Jaundice.
- In Obstructive Jaundice or in extreme case of hepatic jaundice the value decreases.
- In Hemolytic Jaundice the amount of bile pigments in feces increases.
Note : –
- 1. Increased urobilinogen in urine and absence of bilirubin in urine are strongly suggestive of Hemolytic Jaundice.
- 2. Absence of urobilinogen but presence of bilirubin in urine is strongly suggestive of Obstructive Jaundice.
Tests based on Metabolic function of liver
Tests based on carbohydrate metabolism
- Since liver is involved in glycogenesis and in the conversion of other sugars to glucose, the abnormality in these functions may lead to hepatic disease.
- The various tests based on carbohydrate metabolism are as follows :
- Glucose Tolerance Test
- Galactose Tolerance Test
- Fructose Tolerance Test
- Epinephrine Tolerance Test
- Test based on abnormalities of lipids :
- Determination of Serum Cholesterol and cholesterol ester and their ratio. (Normal ratio of free & esterified cholesterol is 30:70 )
- Test based on detoxification function:
- Hippuric acid test:
- Reduction in hippuric acid excretion indicates liver damage.
- Estimation of blood urea & ammonia.
Tests based on Synthetic function of liver:
- Serum albumin
- Ceruloplasmin
- A1-Antitrypsin
- Haptoglobin
- A2-Macroglobin
- Transferrin
- A-Fetoprotein
- Prothrombin time (PT)
- Electrophoretic separation of plasma proteins
Estimation of total plasma proteins & A:G ratio.
- Many plasma proteins and coagulation proteins are synthesized in liver and decreased synthesis of these proteins in pathological conditions affecting liver will lead to decrease in their plasma concentration.
- Since albumin has a fairly long half-life of 20 days, in all chronic diseases of the liver, the albumin level is decreased & A:G ratio will be reversed due to hypo-albuminemia & associated hypergammaglobulinemia.
Estimation of plasma fibrinogen.
Determination of Prothrombin Time (PT):
Normally PT is 14-16 seconds. It increases in liver diseases (decrease in concentration of plasma clotting factors).
Tests based on Enzyme Activity of Liver
Liver cells contain many enzymes which are released into blood in hepatic damage. Measuring of the levels of these enzymes can be used to assess the liver function & in the diagnosis of various liver diseases.
Most commonly & routinely test employed in laboratories are two :
Estimation of ALT & AST and
Estimation of Serum ALP.
Enzyme Aminotransferases (ALT, AST)
The levels of ALT & AST in serum are elevated in all liver diseases but ALT is more sensitive & reliable.
Normal levels:
ALT/ SGPT: 5-40 IU/L (cytoplasmic);
AST/ SGOT: 5-45 IU/L (cytoplasmic & mitochondrial).
Very high levels (more than 1000 units) are seen in acute hepatitis (viral & toxic).
Moderate elevation between 100-300 U/L is seen in alcoholic hepatitis.
Minor elevation less than 100 U/L is seen in chronic viral hepatitis ( Hepatitis-C ) & fatty liver.
Estimation of Serum Alkaline Phosphatase (ALP)
Normal range is 3-13 KA Units/dl
Very high levels of ALP are seen in patients with Cholestasis.
Rise in ALP with Bilirubin: Indicator of billliary obstruction (Obstructive jaundice)
Bile duct obstruction induces the synthesis of the enzyme by biliary tract epithelial cells.
Gamma Glutamyl Transferase (GGT)
GGT is clinically important because of its sensitivity to detect alcohol abuse.
GGT level in alcoholic liver disease roughly parallels the alcohol intake.
Increased levels of GGT are observed in chronic alcoholism and biliary obstruction.
5’-Nucleotidase:
Elevated level of 5’-Nucleotidase is seen in obstructive liver disease (hepatobiliary disease).
It’s activity is parallel to that of ALP.
Other Enzymes:
Elevated levels:
- Isocitrate Dehydrogenase (ICD),
- Leucine Amino Peptidase(LAP),
- LDH 4 & LDH5
Decreased levels:
- Choline esterase
Jaundice
- Yellow coloration of sclera and skin.
- Elevated serum bilirubin beyond 2mg/dl.
- Hemolytic: Increased Hemolysis of erythrocytes
- Malaria, sickle cell anemia
- Hepatic jaundice: Dysfunction of the liver
- Viral hepatitis, cirrhosis, toxins & poisons
- Obstructive jaundice:
- Eg: Obstruction in the bile duct
Biochemical changes in Jaundice:
| Test name | Hemolytic | Obstructive | Hepatic |
| Serum Bilirubin | unconjugated ↑ | conjugated ↑ | both ↑ |
| Van den Berghs | Indirect postive | Direct positive | Biphasic |
| Bile pigments in urine | Urobilinogen | Conjugated bilirubin | Urobilinogen and conjugated bilirubin |
| Serum Enzymes | ALT, AST, ALP — | ALP↑↑,
ALT, AST marginal ↑ |
ALT, AST ↑↑
ALP marginal ↑ |
Kidney Function Tests
Functions of Kidney
- Maintenance of homeostasis:
- Regulation of water-electrolyte and acid-base balance in the body.
- Excretion of metabolic waste products
- Urea, creatinine, Uric acid, sulfate and phosphate
- Retention of substances vital to the body
- Glucose, amino acids
- Hormonal functions: Endocrine
- Erythropoietin, Calcitriol, Renin
Kidney/Renal function tests: May be divided into four groups.
- Tests to assess glomerular function
All the clearance tests (creatinine, urea and so on) are useful in measuring the glomerular filtration rate (GFR). Measuring the proteinuria reflects glomerular permeability.
- Tests to assess tubular function
Urine concentration and dilution tests, urine acidification test and secretion tests are used to text tubular function.
III. Analysis of blood/serum
Estimation of blood urea, serum creatinine, protein and electrolytes are often used to assess renal function.
- Complete urine analysis
Examination of urine for volume, pH, specific gravity, osmolality and presence of any abnormal constituents is also useful to assess the kidney function.
Tests to assess Glomerular functions of kidney
Clearance tests:
- Measurement of GFR.
- Most useful in assessing the renal function.
- Clearance may be defined as the volume of plasma that would be completely cleared of substance per minute.
- Expressed as ml/minute
Creatinine clearance test:
Creatinine clearance may be defined as the volume of plasma that would be completely cleared of creatinine per minute.
U × V
C = −−−−−−
P
U = Urine concentration of creatinine (mg/dl)
V = Urine output in ml/min (24-hour urine volume divided by 24 × 60)
P = Plasma concentration of creatinine (mg/dl)
Reference volumes: The normal range of creatinine clearance is about 120–145 ml/min.
Diagnostic application:
- A decrease in creatinine clearance (<75% normal) indicates a decreased GFR reflecting renal damage.
- Useful for early detection of impairment in kidney function, before clinical manifestations seen.
- Higher than GFR, as it is secreted by the tubules
Urea clearance test:
Urea clearance is defined as the volume of plasma that would be completely cleared of urea per minute. It is calculated by:
U × V
Cm = −−−−−−
P
Cm = Maximum urea clearance
U = Urea concentration in urine (mg/dl)
V = Urine excreted per minute in ml
P = Urea concentration in plasma (mg/ml)
The above calculation is applicable when the output of urine is more than 2 ml per minute. This is referred to as maximum urea clearance (Cm) and the normal value is about 75 ml/min.
Diagnostic interpretation:
- A urea clearance value below 75% normal indicates renal damage.
- Urea after filtered by the glomeruli, it is partially reabsorbed by the tubules, So it is less than GFR.
- It is also influenced by protein content of the diet.
- Urea clearance is not as sensitive as creatinine clearance for assessing renal function
Clearance Tests: External
- Inulin : Plant carbohydrate: Fructosan
- Diodrast
- PAH (Para Amino Hippuric Acid)
Diagnostic importance: The normal inulin clearance rate is 125 ml/min. A comparison of the clearance of a given substance with the clearance of inulin provides information about the renal transport processes.
Tests for Tubular function of Kidney
- Specific gravity and osmolality of urine
- Simplest test for tubular function
- Accurate measurement of specific gravity depends on concentration of solutes in urine.
- Urine concentration test
- Involves the measurement of specific gravity of concentrated urine sample.
- Urine dilution test
- Involves the measurement of specific gravity of diluted urine sample
- More sensitive than concentration test.
Analysis of Blood/Serum
- Estimation of blood urea (15-40 mg/dl) and serum creatinine (0.7-1.5 mg/dl).
- Less sensitive than clearance tests
- Serum creatinine is better indicator of renal function than serum urea.
- GFR must fall to 50% of its normal value before significant increase in urine creatinine occurs.
- Normal serum creatinine level does not necessarily means all is well with the kidney.
Complete Urine analysis
Physical examination- Color, Appearance, Odor, pH, Specific gravity
Chemical analysis for abnormal constituents in urine sample: Glucose, Proteins, Bile salts , Bile pigments, blood, ketone bodies
Choice of Renal function tests:
Routine urine examination followed by blood urea and serum creatinine estimation and finally specific test to assess tubular and glomerular function.