What happens to the fat we take in meals? When we eat fat, it is digested and absorbed in our gastrointestinal tract. Some fat is not absorbed and excreted. Fat is one of the three macronutrients of human food, along with carbohydrates and proteins. Fat is a very good source of energy and essential for cell formation and vitamin absorption. It is vital for good health. However, an excess of fat is hazardous for our health. Let us delve into the fate of fat in our body. Digestion of fat: Lipids are large molecules, and unlike carbohydrates and proteins, they are not soluble in water and do not mix with the watery blood. So, they like to cluster together in large droplets in a liquid surrounding the gastrointestinal tract. The digestive process breaks those large droplets of fat into smaller droplets, and then enzymes digest lipid molecules using enzymes called lipase. In the mouth: Chewing breaks food into smaller particles and mixes them with saliva. Lingual lipase be
Liver Function tests
This article
discusses different tests to diagnose liver diseases. Here, learn about the tests, procedures, indications,
and more.
Keywords: A/G ratio |SGPT| SGOT | Alkaline phosphatase| Alpha-fetoprotein| Hippuric acid test| Thymol turbidity test| Galactose
Index
Table of contents
|
1. |
Introduction |
|
2. |
Classification of
tests |
|
3. |
Recent advance |
|
4. |
Clinical |
|
5. |
Links |
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Introduction:
Liver function tests (LFTs) are blood tests that give information about the functional conditions of a patient's liver. For this, venous blood (collected in the morning after 12 hours of fasting), stool, and urine are tested.
 |
| Position of the liver in the human body This Photo is by an unknown author and is Licensed under CCBY. |
Indications of liver function tests are :
Unexplained fatigue,
lethargy, weakness,
Diagnose and treat jaundice,
Determine the causes of dark-colored urine, light-colored stool, abdominal pain,
In alcoholics and persons with a family history of congenital liver disease.
Utility:
1. Many
biochemical tests detect liver dysfunction and disease.
2. They
determine the degree of liver damage caused by the disease, drugs, or alcohol.
3. They are helpful
in the evaluation and management of liver diseases and
4. They help monitor the response to treatment.
The standard liver panel includes the following:
Estimation
of :
Total
bilirubin level,
Alaline transaminases (ALT or SGPT) ,
Aspartate
transaminases (AST or SGOT),
(AST/ ALT) ratio,
(ALP) alkaline phosphatase,
Gamma-glutamyltransferase (GGT),
Albumin, Globulin, and A/G ratio.
Other tests
may be essential with LFT to detect specific causes e.g.
Estimation
of 5Nucleotidase a glycoprotein
Analysis
of ceruloplasmin-an acute-phase protein,
Assessment
of α- fetoprotein (AFP),
Coagulation
test –International normalized ratio INR,
Analysis
of lactate dehydrogenase.
In liver function
tests, only a few tests inform about the liver's functions, while others indicate the liver's and biliary tract's cellular integrity.
Some tests
determine the status of liver functions, e.g.
(albumin synthesis),
Some tests indicate cellular integrity of the liver ( transaminases. ),
Some tests
inform about the functions of the biliary tract (alkaline phosphatase, gamma-glutamyl
transferase).
So it is clear
that some of these tests do not measure function; they may be called liver tests
or liver chemistries.
1.The liver transaminases are valuable
biomarkers of liver injury. They are : Aspartate transaminases (AST or SGOT), Alaline transaminases (ALT
or SGPT).
Measurements
of plasma protein: Albumin, Globulin, A/G ratio.
The liver
synthesizes albumin, which is the main plasma protein. The albumin level decreases
when the liver is not working correctly, e.g., chronic liver disease-cirrhosis
of the liver. An alternative to albumin measurement is the pre-albumin measurement,
which detects acute changes as its half-life is about two days compared to the half-life
of albumin, which is about two weeks.
Globulin is the
second most abundant plasma protein. It
is synthesized from plasma cells and not from the liver. So in liver diseases,
its concentration is not affected. As the amount of albumin decreases, but the
amount of globulin remains unaltered, not reduced, the A/G ratio rises. The
average value is 1.7/1. The ratio decreases
In liver insufficiency, and in
advance, liver disease may be A/G ratio may reverse.
Normal range
of
|
|
Name |
range |
|
|
1. |
Total plasma protein |
6.----8 gm./dL |
|
|
2 |
Serum albumin |
3.5---5gm/dL |
|
|
3 |
Serum globulin |
2- 3gm/dL |
|
|
4. |
Serum fibrinogen |
0.3 gm /dL |
|
|
5. |
Serum prothrombin |
0.04gm /dL |
|
In liver
insufficiency, except for serum globulin concentration of all proteins falls.
The Thymol
turbidity test is a laboratory test for the non-specific measurement of
globulin.
Add 1 volume
of serum to 60 volumes of a buffer supersaturated with thymol. Thymol–globulin interaction results in
turbidity. –a marked increase in thymol turbidity occurs in viral hepatitis and chronic
liver disease.
Another use
of this test is in the differential diagnosis of jaundice.
Today thymol
turbidity test is rarely used.
Total
bilirubin: Measurement of Total bilirubin
Total
bilirubin =Conjugated +unconjugated bilirubin.
Normal
levels:
Total bilirubin: 1.2 mg/dl of blood.
Unconjugated
bilirubin: 0.9 mg/dl of blood.
Conjugated
bilirubin: 0.3 mg/dl of blood.
The causes of
the increase in unconjugated bilirubin are the overproduction of bilirubin due to the:
1. Reabsorption
of hematoma, ineffective erythropoiesis-increased red blood cell destruction,
2. Reduced hepatic
uptake of the unconjugated bilirubin.
3. Reduced conjugation
of bilirubin-‘Gilbert syndrome' and 'Crigler Najjar syndrome.'
The
bilirubin level is measured by a transcutaneous bilirubinometer or bilimeter.
In the liver, the insufficiency level of blood ammonia ( normal range is20-80 μg/dL.) and urine ammonia (normal range is 400-1200
mg/day)increases, but blood urea(normal range is 20-45 mg/dL) decreases as the liver
converts ammonia into urea.
Bilirubin
and bile salts are absent when the liver is normal, but they are present in
urine in liver insufficiency.
Urine
urobilinogen normal <4 mg/day. In the early
case of liver insufficiency, it increases, but in the advanced case, it is
absent.
Stercobinogen
in stool normal is 20-250 mg/ dL; in early liver disease, it is in excess, but
in the advanced stage, it is absent.
Usually, less
than <7% ingested fat is excreted in the stool, but it
may go as high as 40% in liver diseases causing steatorrhoea-
bulky, foul-smelling stool.
ALT (SGPT) is
present mainly in the liver but may be in the kidneys, heart, and
muscles. Its average level is 5-55 IU/L. of serum. A rise of up to 500 IU/L is
specific for the liver. It can be due to hepatitis, toxins, and ischemic liver
injury.
Two isozymes
of AST (SGOT) are present, 1. Mitochondrial specific for myocardial infarction, and 2.Cytoplasmic, specific for liver cirrhosis. The normal range is 5-40 IU/L
of serum. This is not very specific.
AST/ALT
ratio increases liver dysfunction.
Alkaline
phosphatase (ALP) is mainly present in the
biliary ducts of the liver. Its average level is 20-140 IU/L of blood. In liver disease, the increase is slight, but
in biliary disease –the obstruction increase is more.
Alpha-fetoprotein
(AFP) normal range is 10 ng/ml to 20 ng/ml. A very high blood level of 400-500 ng/mL indicates hepatocellular carcinoma and other cancers.
Coagulation the test:-The liver synthesizes many coagulation factors –their concentrations
decrease in insufficiency of the liver. International normalized ratio (INR) can be
used as a marker of synthetic functions of the liver as it includes factor VII.
Prothrombin
time (average is 11-15 sec) increases in liver insufficiency. The liver
cannot synthesize prothrombin from vitamin K injection.
Hippuric
acid test: In the liver and kidneys, sodium benzoate is conjugated with glycine
and forms hippuric acid.
The subject
ingests 6 gm of sodium benzoate. In normal conditions, 2.7-3.5 gm of sodium
benzoate is excreted in urine as hippuric acid in the next 4 hours. In liver
insufficiency, hippuric acid excretion decreases, provided kidneys are normal. Nowadays, it is not in use.
Bromsulphalein
(BSP) excretion test: BSP in a dose of 5
mg /kg body weight is given by I.V. route, then blood samples are collected
after 5 and 45 minutes. After 5 minutes, the blood concentration falls to 85%, and after 45 minutes to 5% in a normal subject. If the blood concentration of dye is
>10% liver is not working correctly.
BSP is
phenol and tetra bromsulphalein disodium sulphonate. It is removed by normal
hepatocytes from the blood and excreted in bile. This test is not in use.
Galactose Index: The subject ingests 40 gm of galactose. Blood galactose is measured half-hourly for two hours, i.e., four values are obtained. The sum of the four values is usually 70-160 mg/dL.
Estimation of fat: Normal ranges are as follows:
|
Sr.no |
Name |
Normal range |
|
|
1. |
Cholesterol |
120-200 mg/dL |
|
|
2. |
Triglyceride |
40-160 mg/dL |
|
|
3. |
HDL |
40-60 mg/dL |
|
|
4. |
LDL |
<150 mg/dL |
|
|
5. |
VLDL |
<30mg/dL |
|
Many factors affect their average values.
Ultrasound scans, Isotope scans, CAT scans, liver biopsy, etc., are not included in the liver function tests but are very helpful in diagnosing liver diseases.
Hashtags: A/G ratio# SGPT # SGOT# Alkaline phosphatase# Alpha-fetoprotein# Hippuric acid test# Thymol turbidity test# Galactose Index.
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