Liver Function Tests
(LFTs)
Major Metabolic Functions of the Liver
• Synthetic functions
-
Proteins: plasma proteins albumin, globulins, coagulation factors…etc )
Lipids: cholesterol, triglycerides, fatty acids, phospholipids & lipoproteins (VLDL)
Carbohydrates: glycogen synthesis & gluconeogenesis
• Detoxification & excretion functions
- Detoxication of ammonia to urea (urea cycle)
- Billirubin conjugation & excretion into bile
- Excretion of cholesterol into bile
- Drug detoxication & excretion into bile
• Storage Function
- Storage of fat soluble vitamins (vitamins A, D, E & K)
-
Storage of vitamin B12
• Production of bile salts
- Help digestion of lipids
Liver function tests (LFTs)
Overview
LFTs are blood tests used to help to diagnose & monitor disease or damage of the liver
The tests measure the levels of certain enzymes & proteins in blood
Some of these tests measure how well the liver is performing its normal functions of producing
protein & clearing billirubin.
Other liver function tests measure enzymes that liver cells release in response to damage or
disease.
However,
1- Conditions other than liver disease or damage can lead to abnormal liver function test results
2- Test results can be normal in people who have liver disease or damage
Liver function tests can be used to:
1- Check certain enzymes & proteins levels in blood that if are higher or
lower than normal can indicate liver problems (diagnosis)
2- Screen for liver infections, such as hepatitis
3- Monitor the progression of a liver disease, such as viral or alcoholic
hepatitis & determine how well a treatment is working (prognosis)
3- Measure the severity of a liver disease especially liver cirrhosis
4- Monitor possible side effects of medications on liver
Routine Liver Function Tests (LFTs)
1- Serum Albumin
2- Blood Liver Enzymes:
Alanine amino transferase (ALT)
Aspartate amino transferase (AST)
Gamma glutamyl transferase (GGT)
Alkaline phosphatase (ALP)
3- Blood Billirubin (total, direct & indirect)
4- Blood Coagulation Factors (prothrombin & others)
Prothrombin Time (PT)
Others:
Markers of liver fibrosis
Serum Albumin
• Albumin is present in higher concentrations than other plasma proteins
( ~ 40 g/L in normal adults).
• Albumin is synthesized in the liver & has a half-life of 20 days.
• Very small amounts of albumin cross the glomerular capillary wall.
Accordingly, no more than traces of albumin may normally appear in urine
that can not be detected by ordinary laboratory means.
• Albuminuria :
In this case, albumin can be detected in urine by ordinary laboratory means
due to physiological or pathological conditions.
Serum Albumin cont.
Causes of hypoalbuminemia
Artfuctual : Diluted sample
Physiological : Pregnancy - Recumbence
Decreased amino acids : Reduced essential amino acids in diet & reduced synthesis of nonessential amino acids
Malnutrition
Malabsorption.
Increased catabolism :
Surgery
Trauma
Infections
Defective synthesis in liver: Chronic liver diseases
Increased loss : From the kidney:
Nephrotic syndrome
From GIT:
Protein loosing entropathies
Blood Aminotransferases
(ALT & AST)
•
Aminotransferases (ALT & AST) are normally intracellular enzymes
•
Plasma contains low levels of aminotransferases representing release of cellular
contents during normal cell turnover
•
Elevated blood levels of aminotransferases indicate damage to cells rich in these
enzymes (as disease to tissue or physical trauma )
•
Blood AST & ALT are of particular diagnostic value
Causes of elevated levels of blood ALT & AST
1- Viral , toxic or alcholic hepatitis
ALT & AST are elevated even before appearance of clinical signs (jaundice) & symptoms.
Marked increase in ALT & AST (Up to 20 - 50 - may reach up to 100 folds).
Peak values between 7 – 12 days of onset of the disease
In viral hepatitis, ALT is much elevated than AST
2- Cirrhosis (chronic liver diseases)
ALT & AST are increased to levels depending on the status of the process
(Moderate increase (up to 4 – 5 folds)
In chronic cases, AST is much elevated than ALT.
3- Obstructive jaundice:
ALT & AST are increased up to 3 folds (moderate increase)
4- After
alcoholic or drug intake (transient slight to moderate increase).
Alanine amino transferase (ALT)
ALT is more liver specific than AST.
ALT rarely increases in lesions other than the liver parenchymal
ALT elevations persist longer than do AST.
Aspartate transaminase (AST)
Blood levels of AST are increased with many diseases of various organs:
1- Liver diseases
2- Myocardial infarction (MI)
However, ALT may be also increased if liver congestion occurs secondary to congestive heart failure
3 - Progressive skeletal muscular dystrophy
4- Crush injury
5- Hemolytic diseases
6- Artifact: in hemolysed samples or if serum separation is delayed
Gamma glutamyl transferase (GGT)
GGT present in blood originates primarily from hepatobillary system
Causes of increased blood GGT:
1- Induction of GGT synthesis by these cells occurs without cell damage
by alcohol or drugs as anticonvulsants , phenobarbitone & phenytoin
2- Biliary obstruction :
GGT is markedly increased with obstructive jaundice (5 – 30 folds)
Increase earlier (more sensitive) than ALP
Persists longer than ALP
3- Viral, toxic & alcoholic hepatitis :
Increase is only 2 – 5 folds (less sensitive than ALT & AST)
4- Primary and secondary liver tumors:
GGT is elevated earlier than other enzymes in liver neoplasm.
Secondaries of other organ tumors in the liver can be early detected by
elevated GGT. (arouse suspicious that the diseases is metastatic to liver)
Alkaline Phosphatase (ALP)
Alkaline phosphatases (ALP) are group of enzymes that hydrolyze organic phosphates at
high pH (9 – 10.5)
Main Sources of ALP:
1- Cells of hepatobiliary tract (hepatocytes adjacent to the biliary canalculi)
Activity in the liver is localized on those parts of the cell membrane of the
parenchymal cell adjoining the biliary canalculi
2- Osteoblasts of bone :
he metabolic function of ALP is probably important for bone calcification.
Other Sources: Intestine and placenta & renal tubules
Alkaline Phosphatase (ALP) cont.
Clinical significance of increased serum ALP activities:
1-Physiological increase of ALP:
During periods of active bone growth in infancy and at puberty
Preterm infants total ALP is increased to 5 times the upper reference limit of adults
due to bone isoenzymes.
In children under 3 years, total ALP activity is increased up to 2.5 times the upper limit
Increased twice, during the second and third trimesters of pregnancy (placental ALP).
Alkaline Phosphatase (ALP) cont.
2- Pathological increase of ALP:
A- Bone causes (due to increased osteoblastic activity):
Tumors (osteogenic)
Paget`s Disease of bone
Marked increase , may be 10 – 25 folds)
due to osteoblastic cells action trying to rebuild bone that is resorped by activity of
osteoclasts
Primary osteogenic tumors
Secondary malignant deposits in bone if causing osteoblastosis e.g. cancer
prostate causing deposits in bones (osteoblastic tumor)
Rickets & osteomalacia (vitamin D deficiency)
Primary & secondary hyperparathyroidism (increased PTH)
Healing of bone fractures
Alkaline Phosphatase (ALP) cont.
B-Hepatobiliray tract
liver diseases with involvement of biliary tract
1- Obstructive jaundice (intrahepatic or extrahepatic)
Extrahepatic cholestiasis : (Marked increase, up to 10 – 12 folds)
Due to obstruction of to the flow of bile through the biliary tract by:
Stones, inflammation of biliary tract or pressure from outside by cancer head of pancreas.
Intrahepatic cholestiasis: (Moderate increase , ~ 3 -5 folds)
Bile secretion from the hepatocytes into the canalculi is impaired by:
Drugs (chlorpromazine), alcohol, inflammation of the biliary tract (cholangitis).
2- Viral, toxic & alcoholic hepatitis
Mild to moderate increase, less than 3 folds (ALP may be may be normal)
If ALP is elevated due to a bone disease
In this case, GGT is (or may be) normal
i.e. GGT is used to ascertain whether increased ALP is due to
bone or hepatobiliary disease
Coagulation factors
• The liver makes many of the proteins (prothrombin & other clotting factors)
needed to make blood clot
• In certain liver disorders the liver cannot make enough of these proteins and
so blood does not clot so well.
Therefore, blood clotting tests may be used as a marker of the severity of
certain liver disorders
• In liver disease, the synthesis of prothrombin & other clotting factors is
diminished,  prolonged prothrombin Time (PT)
• This may be one of the earliest abnormalities seen in hepatocellular
damage, since prothrombin has a short half-life (~ 6 hours)
Makers of Liver Fibrosis
• Procollagen type III terminal peptide
• Hyaluronic acid (hyaluronin)