Common Tests
Information on medical tests, including how to prepare, what to expect, and what the results mean.
BLOOD TESTS
Cholesterol and Triglycerides Tests
Test Overview
Cholesterol and triglyceride tests are blood
tests that measure the total amount of fatty
substances (cholesterol and triglycerides)
in the blood.
Cholesterol travels through the blood attached
to a protein. This cholesterol-protein package
is called a lipoprotein. Lipoprotein analysis
(lipoprotein profile or lipid profile) measures
blood levels of total cholesterol, LDL cholesterol,
HDL cholesterol, and triglycerides.
- Cholesterol The body uses cholesterol
to help build cells and produce hormones.
Too much cholesterol in the blood can build
up along the inside of the artery walls,
forming what is known as plaque. Large amounts
of plaque increase your chances of having
a heart attack or stroke.
- HDL (high-density lipoprotein) cholesterol
helps remove fat from the body by binding
with it in the bloodstream and carrying it
back to the liver for disposal. It is sometimes
called “good” cholesterol. A
high level of HDL cholesterol may lower your
chances of developing heart disease or stroke.
- LDL (low-density lipoprotein) cholesterol
carries mostly fat and only a small amount
of protein from the liver to other parts
of the body. It is sometimes called "bad
cholesterol." A high LDL cholesterol
level may increase your chances of developing
heart disease.
- VLDL: (very low-density lipoprotein) cholesterol
contains very little protein. The main purpose
of VLDL is to distribute the triglyceride
produced by your liver. A high VLDL cholesterol
level can cause the buildup of cholesterol
in your arteries and increases your risk
of heart disease and stroke.
- Triglycerides are a type of fat the body
uses to store energy. Only small amounts
are found in the blood. Having a high triglyceride
level along with a high LDL cholesterol may
increase your chances of having heart disease
more than having only a high LDL cholesterol
level.
Some medical experts recommend routine cholesterol
and triglyceride testing to screen for problems
that affect the way cholesterol is produced,
used, carried in the blood, or disposed of
by the body. Others may choose to routinely
measure only total cholesterol and HDL levels.
- National Cholesterol Education Panel (NCEP)
guidelines for cholesterol screening
- U.S. Preventive Services Task Force (USPSTF)
guidelines for cholesterol screening
- American College of Physicians (ACP) guidelines
for cholesterol screening
- American Heart Association guidelines for preventing coronary artery disease and stroke
Blood Glucose
Test Overview
A blood glucose test measures the amount of a type of sugar, called glucose, in your blood. Glucose comes from carbohydrate foods. It is the main source of energy used by the body. Insulin is a hormone that helps your body use and control the amount of glucose in your blood. Insulin is produced in the pancreas and released into the blood when the amount of glucose in the blood rises.
Normally, your blood glucose levels increase slightly after you eat. This increase causes your pancreas to release insulin so that your blood glucose levels do not get too high. Blood glucose levels that remain high over time can damage your eyes, kidneys, nerves, and blood vessels.
Several different types of blood glucose tests are used.
- Fasting blood sugar (FBS) measures blood glucose
after you have not eaten for at least 8 hours.
It often is the first test done to check for
diabetes.
- 2-hour postprandial blood sugar (2-hour PC)
measures blood glucose exactly 2 hours after
you eat a meal.
- Random blood sugar (RBS) measures blood glucose
regardless of when you last ate. Several random
measurements may be taken throughout the day.
Random testing is useful because glucose levels
in healthy people do not vary widely throughout
the day. Blood glucose levels that vary widely
may indicate a problem. This test is also called
a casual blood glucose test.
- Oral glucose tolerance test is used to diagnose prediabetes and diabetes. An oral glucose tolerance test is a series of blood glucose measurements taken after you drink a sweet liquid that contains glucose. This test is commonly used to diagnose diabetes that occurs during pregnancy (gestational diabetes). For more information, see the medical test Gestational Diabetes. This test is not commonly used to diagnose diabetes in a person who is not pregnant.
PROSTATE
Prostate-Specific
Antigen (PSA)
Test Overview
A prostate-specific antigen (PSA) test measures the amount of prostate-specific antigen in the blood. PSA is released into a man's blood by his prostate gland. Healthy men have low amounts of PSA in the blood. The amount of PSA in the blood normally increases as a man's prostate enlarges with age. PSA may increase as a result of an injury, a digital rectal exam, sexual activity (ejaculation), inflammation of the prostate gland (prostatitis), or prostate cancer.
Prostate cancer often grows very slowly, without causing major problems. Detecting prostate cancer early and treating it may prevent some health problems and reduce the risk of dying from the cancer. However, some treatments for prostate cancer can cause other problems, such as controlling urination (incontinence) or erection problems (erectile dysfunction). Some men may choose not to have a PSA test or treat prostate cancer if it is detected. For example, a man older than age 75 who has no bothersome symptoms of prostate cancer may choose not to treat the cancer if it is found, so he would not need a PSA test.
LIVER
Alanine Aminotransferase (ALT)
Test Overview
An alanine aminotransferase (ALT) test measures
the amount of this enzyme in the blood. ALT is
found mainly in the liver, but also in smaller
amounts in the kidneys , heart , muscles, and pancreas . ALT formerly
was called serum glutamic pyruvic transaminase (SGPT).
ALT is measured to see if the liver is damaged
or diseased. Low levels of ALT are normally found
in the blood. However, when the liver is damaged
or diseased, it releases ALT into the bloodstream, which makes
ALT levels go up. Most increases in ALT levels are caused by liver
damage.
The ALT test is often done along with other tests
that check for liver damage, including aspartate
aminotransferase (AST), alkaline phosphatase, lactate dehydrogenase
(LDH), and bilirubin. Both ALT and AST levels are reliable tests
for liver damage.
Aspartate Aminotransferase (AST)
Test Overview
An aspartate aminotransferase (AST) test measures
the amount of this enzyme in the blood. AST is normally found
in red blood cells, liver, heart, muscle tissue, pancreas, and
kidneys. AST formerly was called serum glutamic oxaloacetic transaminase
(SGOT).
Low levels of AST are normally found in the blood.
When body tissue or an organ such as the heart or liver is diseased
or damaged, additional AST is released into the bloodstream. The
amount of AST in the blood is directly related to the extent of
the tissue damage. After severe damage, AST levels rise in 6 to
10 hours and remain high for about 4 days.
The AST test may be done at the same time as a
test for alanine aminotransferase, or ALT. The ratio of AST to
ALT sometimes can help determine whether the liver or another
organ has been damaged. Both ALT and AST levels can test for liver
damage.
PRO-TIME
Prothrombin Time
Test Overview
Prothrombin time (PT) is a blood test that measures
how long it takes blood to clot. A prothrombin
time test can be used to check for bleeding problems.
PT is also used to check whether medicine to prevent blood clots
is working.
About 12 blood clotting factors are needed for
blood to clot (coagulation). Prothrombin, or factor
II, is one of the clotting factors made by the liver. Vitamin
K is needed to make prothrombin and other clotting factors. Prothrombin
time is an important test because it checks to see if five different
blood clotting factors (factors I, II, V, VII,
and X) are present. The prothrombin time is made longer by:
- Blood-thinning medicine, such as heparin. Another
test, the activated partial thromboplastin time
(APTT) test, is a better test to find out if
the right dose of heparin is being used.
- Low levels of blood clotting factors.
A change in the activity of any of the clotting factors. - The absence of any of the clotting factors.
- Other substances, called inhibitors, that affect
the clotting factors.
- An increase in the use of the clotting factors.
An abnormal prothrombin time is often caused by liver disease or injury or by treatment with blood thinners.
Another blood clotting test, called partial thromboplastin
time (PTT), measures other clotting factors.
Partial thromboplastin time and prothrombin time
are often done at the same time to check for bleeding problems
or the chance for too much bleeding in surgery.