What is the blood test for cancer? What is occult blood stool test?

Why does the doctor always order basic blood and urine tests for cancer? 

These simple tests, sometimes called CBC (complete blood count), SMA 12 (serum factors), and UA (urine analysis), give the doctor a great deal of basic information about your general health problems. They can usually be done in the doctor's office.

What does the complete blood count consist of? 

The technician takes whole blood from your vein as well as a blood smear from your finger and uses the samples to check the hemoglobin, white blood cell count, and complete red and white cells in the blood and the platelets. The hematocrit test requires that the blood be spun in a centrifuge and measures (usually on an automatic counting machine with computer printout) the volume of red cells as a percent of the total volume. This test can help detect if anemia is present, though it cannot identify the type of anemia. The hemoglobin test measures the number of grams of red cell pigment in 100 cubic centimeters of blood. A low count is a sign of some type of anemia. The white cell count (listed as WBC) shows the number of white cells per cubic millimeter of blood. Usually an elevation of this count points to infection.

The microscopic examination and count of the blood smear helps to determine the type of infection, type of anemia, or blood clotting conditions. The technician examines the smear to determine the proportions of various types and numbers of white cells (called differential), the size and shape of red cells, and the number of platelets present.

What does the urinalysis tell the doctor? 

The degree of concentration of the urine (weight of urine relative to plain water), called specific gravity (SG), indicates urinary obstruction with kidney damage if the count is low or dehydration if the count is high. Using a simple plastic strip with a series of chemically sensitive patches, the doctor or his nurse or technician can also check the amount of acidity, protein, sugar, and ketones in the urine to diagnose acidosis or alkalosis, kidney damage, diabetes, etc. The microscopic examination of centrifuged urine, called the urine sediment exam, checks for red cells, white cells, kidney cells, crystals, and microorganisms in the urine which might indicate kidney damage, urinary tract infection, or gout.

Are blood tests used for detecting cancer? 

At the present time there is no one blood test which conclusively tells if cancer is present, either for the initial diagnosis of cancer or for monitoring disease recurrence. The tests now available are not sufficiently accurate; they may be negative when no cancer is present and also when it is known that the person has cancer. Sometimes they are positive when cancer is not present. Therefore they are currently being used only along with other cancer detection exams.

Can a blood test detect cancer?


Are monoclonal antibodies being used to detect cancer? 

At present they are being used experimentally. Radioactive antibodies can be sent through the body to seek out specific cancer cells and to attach themselves only to those kinds of cells. The radioactive hot spots, where the antibodies have lodged, can be photographed with x-rays.

Has any progress been made in finding a blood test to detect cancer? 

Progress has been made in identifying what are called biological markers substances present in abnormal amounts in the blood or urine of a person with cancer. Such substances are produced either by the tumor itself or by the patient in response to the tumor tissue. Researchers are still hoping to develop a simple laboratory test, using a sample of blood or urine, to reveal the presence of cancer before other signs appear. Such a test has not yet been developed. However, some techniques presently used in cancer treatment are based on biological markers. For instance, the ability to determine estrogen and progesterone receptors helps doctors decide on treatments for breast cancer. The monitoring of carcinoembryonic antigen (CEA) is useful in determining whether or not colorectal cancer is shrinking or spreading during treatment. Unfortunately, neither of these indicators is useful in detecting the cancer itself. Markers can be produced by diseases other than cancer. They are not sensitive enough or levels remain normal in a certain percentage of cancer patients. Scientists hope that the use of monoclonal antibodies, along with an increased understanding of chromosome changes associated with cancer, will provide an increase in reliable tumor markers in the future.

Is the CEA (carcinoembryonic antigen) test now being used? 

The CEA test detects changes in the body that often accompany cancers. This test is now being used but only in combination with other established procedures for both diagnosing and managing cancer. Although it may be useful as an early indication of recurrence in some patients previously treated for cancer, alone it is not a conclusive test either for initial diagnosis or for monitoring disease recurrence.

What is the blood stool test? 

The blood stool test, also called the occult (hidden) blood test or the guaiac test, detects blood in the stool not visible to the naked eye. Many doctors give you this test to do at home following a regular physical examination. Do ityourself test kits can also be bought at most drugstores. To do the test, you are usually asked to follow a diet containing increased fiber and no meat for several days before and during the stool sampling period. You are also advised not to take aspirin or vitamin C pills during that time. A small amount of feces from three different stools is transferred with an applicator stick to a labeled card. A solution is added to each specimen on the card. If blood is present, the test paper turns from white to blue. If this happens, additional tests must be done to determine whether a precancerous or cancerous condition is present.

Tracking cancer with a blood test

What routine is followed in doing an ECG (EKG) exam? 

The electrocardiogram is an electrical record of the performance of the heart. When the heart muscle contracts and relaxes, changes are produced which can be picked up from the skin surface by electrodes applied to the various parts of the body. This test is part of most routine physical examinations when a patient is past 40, and is a part of most routine hospital examinations. The electrodes round, cold metal discs are smeared with a jellylike substance to heighten conductivity. They are attached to the wrists and ankles. Another disc is used by the operator to move in a series of prescribed positions on the chest. The wires or "leads" record the vertical peaks and horizontal lines made as the heartbeat travels from an upper chamber to the lower chamber of the heart. An inked stylus traces the pattern on graphed paper affixed to a drum that rolls through the electrocardiograph machine. From this tracing, the doctor has a graphic record of the patient's heartbeat.


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