Liver-The Factory of Human Body
Liver has many functions in the body. This factory acts as a storage organ for the absorbed nutrients
and detoxifies drugs and other chemicals. It breaks down the complex carbohydrates into its simplest
form- glucose, as well as stores fat soluble vitamins. The majority of the serum proteins such as albumin,
coagulation factors, plasma Carrier proteins, and lipoproteins are synthesized by the liver. Other functions
that are carried out by this organ are, excretion of toxic ammonia and the synthesis of bile acid which
functions as an emulsifier essential for absorption of fats and fat-soluble nutrients. Any change in liver
functioning disrupts the array of activities performed by it.
Importance Of Enzyme Detection
laboratory tests for enzymes are fully automated and are commonly accepted as a part of routine
annual checkup. Screening tests include measurement of serum alanine aminotransferase (ALT),
aspartate aminotransferase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transferase
(GGT). The challenges faced by the physicians are the patients having abnormal result on measurement
of either serum aminotransferases or alkaline phosphatase that is otherwise asymptomatic.
In asymptomatic patients, persistent elevation of liver enzymes require further test to detect the
cause of hepatobiliary (concerned with liver along with bile duct and gall bladder injury since the
magnitude of enzyme does not always reflect severity of disease. Pattern of enzyme elevations are
essential for proper evaluation of the condition. The pattern can either be Hepatic, wherein the
elevation of enzymes results from liver tissue damage: or can be Cholestatic, where the bile flow
is obstructed. Elevated levels of alanine aminotransferase and aspartate aminotransferase are
observed in hepatic condition, while cholestatic includes elevation of alkaline phosphatase and
gamma-glutamyl transferase levels.
Enzymes in Action
Alanine Aminotransferase (ALT)
Also known as serum glutamatic pyruvic transaminase (SGPT) ALT is an enzyme produced in different
tissues but prominently in hepatocytes, and hence acts as specific marker of hepatocellular injury or
damage. This enzyme reversibly catalyzes transamination of the alanine to pyruvate, an important
intermediate in cellular energy production. Healthy individuals usually have low levels of ALT in the
circulation as body uses it for breakdown of food into energy. Liver damage results in excessive release
of ALT into blood, much before the onset of jaundice or any other symptom and thus enabling early
detection Elevated ALT level are also associated with reduced insulin sensitivity, adiponectin and
glucose tolerance as well as increased free fatty acids and triglycerides. ALT has a serum half-life
of about 40 to 48 hours.
Normal range
In females: 10-28 U/L; In males: 13-40 U/L
Aspartate Aminotransferase (AST)
Also known as serum glutamic oxaloacetic transaminase (SGOT), AST is an enzyme which carries
out the reversible transfer of an alpha-amino group between aspartate and glutamate which is
important in amino acid metabolism. It is produced in liver cells and also present in heart muscle,
skeletal muscle, kidney tissues, etc. Elevation of AST levels in conjugation with ALT indicates
hepatocellular injury. AST possesses serum half-life of about 16 to 18 hours.
Normal range
In females: 0 - 31 U/L; In males: 0 - 37 U/L
Alkaline Phosphatase (ALP)
It is produced in the membrane of bile ducts lining and are also present in kidney, intestine,
leukocytes, pancreas, bone, etc. This enzyme helps in transportation of lipid in the intestine and
calcification of bone. It is present on the surface of bile duct epithelia, where it is required for fat
digestion. Increase in the levels of ALP is found in condition like Cholestasis, that enhances the
accumulation of bile salts and increases its release from the cell surface. Hence, ALP level rises
late in bile duct obstruction slowly decreases on the resolution of the condition. Children and
adolescents have high levels of ALP in blood due to the ongoing bone growth. Therefore, different
normal reference value ranges of ALP test must be interpreted for children and adults.
Normal range
In females: 42 - 98 U/L; In males, 53 - 128 U/L
Gamma-Glutamyl Transferase (GGT)
It is a microsomal enzyme found in several cells such as hepatocytes (liver cells), biliary epithelial
cells, and other regions such as renal tubules, pancreas and intestine. This enzyme is involved in
glutathione metabolism and carries out the transport of peptides into the cell across the cell
membrane. Due to absence of GGT in bones, they do not play any major role in bones. Elevated
levels of both GGT and ALP are observed in liver diseases. GGT is majorly associated with structural
liver damage, hepatic microsomal enzyme induction.
Normal range
In females: 0 - 38 U/L; In males, 0 - 55 U/L.
AST/ALT ratio
AST/ALT ratio provides more clinical utility than the assessment of elevated levels of AST & ALT
individually. Different conditions can be differentiated on the basis of varying ratios.
1. Ratio helps to differentiate non-alcoholic steatohepatitis (NASH) from alcoholic liver
2. A ratio of less than 1: seen in acute viral Hepatitis and toxic hepatitis
3. A ratio greater than 1: indicates advanced liver fibrosis and chronic hepatitis C infection
4. Ratio greater than 2: is observed in alcoholic hepatitis
5. A mean ratio of 1.4: is found in patients with cirrhosis related to NASH
6. Above 4.5: is observed in Wilson's disease and similar such altered ratio is found even
in Hyperthyroidism.
Liver Function Tests (LFT)
The backbone of liver diagnosis, it is the most commonly used non-invasive screening test for
assessing liver disorders. There are lots of speculations surrounding the name of this test,
it can rightly be called as 'liver injury tests'.
This test includes 3 main parameters
1. Proteins
Serum albumin is synthesized in the liver and its synthesis directly reflects the extent of functioning
of liver cells. Hence, decrease in the level of albumin suggests liver damage. Except for the acute
liver diseases, all other chronic diseases are indicated by decreased albumin level. In case of acute
viral hepatitis, obstructive jaundice, and hepatotoxicity, the albumin levels are normal.
Globulin or gamma globulin proteins, in liver are produced by B lymphocytes of hepatocytes.
Their levels elevate against the chronic liver diseases like chronic active hepatitis, and cirrhosis.
Increased levels of IgG in autoimmune hepatitis, IgM in primary biliary cirrhosis and IgA is in
alcoholic liver disease are observed.
Serum albumin/globulin ratio is also assessed to check the improper functioning of the liver.
Normal range
Total protein: 5.7 - 8.2 g/dl, serum globulin: 2.5-3.4 g/dl, and serum albumin: 3.2-4.8 g/dl.
2. Bilirubin
It is the yellowish substance formed due to lysis of RBCS, which releases hemoglobin that further
splits into heme and globin. This heme part is catabolized to produce bilirubin. Urine samples are
mandatory for examining liver disorders, hemolytic anemia, and neonatal jaundice.
Unconjugated Bilirubin (Indirect): It is hydrophobic in nature and hence is bound to albumin for
its transportation through blood to liver. Increased level is indicative of increased red cell destruction
as in hemolytic anemia.
Normal range 0-0.90 mg/dl.
Conjugated Bilirubin (Direct): In the liver, unconjugated bilirubin gets attached with glucuronic
acid and forms hydrophilic conjugated bilirubin, which is then excreted via bile into the small
intestine. Elevated levels indicate decreased elimination of bilirubin from the liver cells and might
be a result of viral hepatocellular disease, cholestatic injury, intrahepatic cholestasis, primary
biliary cirrhosis, etc.
Normal range 0-0.30 mg/dl.
Total Bilirubin: It is the total count of both conjugated and unconjugated bilirubin. This blood tests
determines elevated level of bilirubin substance that may indicate liver diseases.
Normal range 0.3 -1.20 mg/dl.
3. Enzymes
Elevated levels of the above mentioned enzymes ALT, AST, ALP, and GGT are assessed to detect
liver damage or its dysfunction and disorders associated to liver.
Other Tests
1.5' Nucleotidase (5'NT)
5'NT is an intrinsic membrane transport protein generally disseminated throughout the body,
hydrolyzing the 5'-nucleotides to their corresponding nucleosides. Despite its ubiquitous distribution,
serum concentrations of 5'NT reflect hepatobiliary diseases especially, intrahepatic obstruction.
The advantage of this test over ALP is that, the serum 5'NT activity is not elevated in any other
cases such as, in infancy, childhood, pregnancy, or osteoblastic disorders.
2. Coagulation test
Abnormal or decreased clotting factor synthesis is associated with the impairment of hemostatic
function linked to liver. To assess the liver impairment, clotting profile includes levels of prothrombin
time (PT) and activated partial thromboplastin time (aPTT) which would be a predictive indicator
of abnormal coagulation.
3. Lactate dehydrogenase (LDH)
LDH is an enzyme responsible for the production of energy in the cells as well as majorly found in
heart, liver, kidney, lungs, and in blood cells in high amounts. It can be used as a general indicator
of acute or chronic tissue damage. On damage to liver cells, LDH is released from cells into the
blood circulation, and hence blood LDH levels are considered as an indicator of cell or tissue damage.
LDH can also detected in tissue fluids such as cerebrospinal fluids, peritoneal fluid in the brain
and lung injuries respectively.
Importance of Liver can be understood with the fact that, functional liver failure does not occur
until much of the liver tissue has been damaged, but once it crosses this capacity the damage
is irreparable. Hence, a preventive outlook is very crucial to maintain this super factory called
liver stay healthy and monitor its proper functioning with timely screening.
Testing @ Thyrocare
Thyrocare offers Liver Function Tests Profile for the qualitative and quantitative analysis of serum
proteins, bilirubin and enzymes indicative of liver functioning using advanced and sophisticated
automated technology of Photometry at highly affordable rates.
The only organ with the blessing of regeneration, super power of detoxification & many more
such astonishing functions, deserves utmost care... Love your liver!!
