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This document is NOT intended to provide you with medical advice. You should consult qualified practitioners in your area for such information. |
Our pages about bloods come in two parts with a third page showing a diagram of the various components of the blood. The current page contains descriptive information about the various components of blood and the various tests. Part Two, Sample Reference Ranges for Blood Tests, has a list of commonly used blood tests, their measurement units, and the "normal" range of results at one laboratory some of our members use. In addition, a diagram showing the various components of the blood may be helpful.
We provide this information to help educate patients about the usefulness
of these tests. As usual, you should consult qualified practitioners at
the medical center where you are treated for complete and accurate interpretation
of your own results.
A CBC is a complete blood count. This means that your doctor wants to know the amounts and proportions among the various components of your blood, explained below. The term differential refers to the fact that each person has several different kinds of white cells and each type performs a different function in our bodies. The differential measures each different kind of white cell and calculates the proportion of each as a percentage of all the cells in your blood.
White blood cell count: White blood cells are also called leucocytes (luke-o-sites). The white blood cell count is simply the number of white blood cells in your blood. It is often reported in thousands. Some labs report this as numbers like 4.6, i.e., 4600 white blood cells, while others report it as the whole number, i.e., 4600. Among patients this is frequently called whites, as in "What were your whites today?"
The whites and the differential are the two tools your oncologist uses to help figure out what's happening to your body while you're being treated and how your bone marrow is reacting.
Red blood cell count (also called erythrocyte count): Red blood cells are also called erythrocytes (ee-ree-throw-sites). The red blood cell count is simply the number of red blood cells in your blood. It is also often reported in millions. Some labs report this as 5.5 while others report it as the whole number, 550,000. Patients have also developed their own shorthand for this and often call it "reds".
The reds reflect more about what's happening with the chemistry and physics of your blood as you're being treated. The life of a red in your body is usually about 120 days (4 months).
Hemoglobin: Hemoglobin is the primary component of your red blood cells. This amount is reported as grams per deciliter (a deciliter is 1/10th of a liter). The hemoglobin carries oxygen and carbon dioxide around your bodies. It has one part called heme which contains iron and the characteristic red pigment of your blood called porphyrin (pore-fer-in). The other part is a protein called globin formed from a number of amino acids. The oxygen easily combines with the heme so it can get around to your body's cells. Because the oxygen actually attaches to your hemoglobin, it is important for your doctor to know how much hemoglobin you have.
Hematocrit: Hematocrit is a measure of the "mass" of your red blood cells. In this test, the blood cells and plasma are separated (that's what the word hematocrit means) and the proportion of reds in your whole blood is reported as a percentage. This value is calculated and, as such, is slightly less accurate than a hemoglobin count which is measured directly.
Mean corpuscular volume: This ratio is calculated for your doctor. The equation for the ratio is:
Mean corpuscular hemoglobin: This ratio is also calculated for your doctor and reported in your test results. The equation for this ratio is:
Red cell distribution width: Normal red cells are approximately round and have some variation in their width. But, abnormal variation in size, called anisocytosis (ann-iso-si-toe-sis), together with MCV, helps your doctor determine what kind of anemia you may have.
Platelet count: This is a simple count of the number of platelets in your blood. The result is reported in thousands by most laboratories, for example, 140, or, in other laboratories as the actual number, for example, 140,000. Platelets are critical to clotting and preventing bleeding.
Mean platelet volume: This measures the size of your platelets.
It is reported in femtoliters. Its values, with other information, help
your doctor evaluate low platelet counts.
Differential: Each of the various
kinds of white blood cells performs several different functions.
They include:
Blood chemistry tests
A group of these tests are usually performed together, primarily for cost-savings. For the cost of two or three of the individual tests, it is possible to perform many tests in an automated system. The combination of tests is usually called a chemistry panel, chem panel, or comprehensive metabolic panel. The various blood chemistry tests listed here are ones from the panel as well as some others that are often checked for certain patients.
CO2 content: Determining your CO2 level gives your oncologist an idea about whether your blood is acidic or alkaline. As with several of the tests in this list, this gives your doctor an idea about whether your treatment might be affecting your kidneys. Severe vomiting and severe diarrhea can also affect your CO2 levels. Finally, because some chemotherapy regimens also include diuretics, this can be used to see whether those are affecting you adversely.
Electrolytes
These are tests to be certain that cells in various parts of your body have the chemicals needed to operate properly. Except for calcium and phosphorus which are reported as milligrams per deciliter, electrolytes are reported in micromols per liter. The amount of nearly all these will decline whenever you become dehydrated, such as through sweating, vomiting, and diarrhea. When one or more of these becomes abnormally low, you are likely to develop serious physical problems so part of your treatment, especially during chemotherapy, will include replacing these chemicals.
Calcium: Most of your calcium is stored in your bones and teeth. But, for your muscles to flex, and for your heart to beat (it is, after all, a muscle flexing), your body needs what is called ionized calcium, that is, calcium in a specific form which is NOT part of your bones and teeth. If the level in your blood is abnormally low, your body will draw calcium from your bones and teeth, which can result in other problems. If your calcium is too high, your oncologist will institute specific therapies. See the discussion of phosphorus below as well.
Chloride: This helps your cells operate properly. In between your cells is an area called the extracellular spaces. Molecules that need to move into and out of your cells depend on a process called osmosis, which governs the movement of molecules through permeable membranes, including the walls of your body's cells. Chloride in the extracellular spaces helps osmosis work properly.
Phosphorus: Phosphorus is required together with calcium for your bones. However, some of it is found in other parts of your body as well. It is required so that new bone can be formed. It is also required to metabolize both glucose (the simple sugar found in your blood) as well as lipids (fats). As part of its role in metabolism, it also helps move energy around your body. There must be a balance between calcium and phosphorus in your body. When one increases, the other is decreased by excreting it through your kidneys. So, if you have excess calcium, you may have abnormally low phosphorus and vice versa.
Potassium: Potassium is the principal electrolyte in intracellular fluid, that is, fluid inside your cells. Even if you don't eat any potassium-containing foods (bananas and dark, green leafy vegies for example), your body still excretes potassium. It's quite likely that, if you're unable to eat for a period of time, your body will have a low potassium level and you might require a pill or other medication. Potassium is very important for conducting nerve impulses, for muscle functioning (again, especially the heart), and in the osmosis process mentioned in the discussion of chlorine. A low potassium level can be determined also by looking at an electrocardiogram which will show a U-wave in the absence of the proper amount of potassium. Too high a level of potassium can be fatal.
Sodium: Sodium is the principal electrolyte in our blood. The other electrolytes are there but not as prominant. Like potassium and chlorine, it is important in cell osmosis. It is also important in the transmission of nerve impulses. A number of compounds work at keeping the level of sodium in our bodies at an appropriate level and, even if we become dehydrated for some reason, it is quite difficult to reduce the amount of sodium circulating in our blood without fundamental, underlying health problems.
Glucose and related tests
Glucose: Glucose is a simple sugar. For anything you eat to be used by your body for energy, it needs to be converted to glucose. Not only are "big" sugars such as sucrose (found in granular sugar) or fructose (found in soft drinks and other "sugary" treats) converted to a simpler form, but lipids (fats) and complex carbohydrates (such as grains) are also converted to glucose. The big sugars convert to glucose most quickly and lipids convert most slowly to glucose. Complex carbohydrates convert to glucose at an intermediate rate. Glucose is reported in milligrams per deciliter. Elevated glucose levels, as in diabetes, can interfere with proper metabolism of your chemotherapy drugs and can otherwise interfere in your life.
Glycosylated hemoglobin: Glycosylated (gli-cos-i-lated) hemoglobin is a measure of your long-term control of blood glucose levels. This test is primarily used for monitoring diabetics. As reds circulate, they combine some of the glucose in your blood with hemoglobin to form a special form of hemoglobin called glycohemoglobin. The amount of this as a percentage of your total hemoglobin is reported in your test results. If good control of blood glucose levels does not occur, this test will indicate the situation to your doctor.
Metabolic products
Metabolic products are "waste products" of your cells. They need to be removed from your body. Your blood is one way that these are removed from your cells and the areas around them and moved to your body's garbage dumps for processing. The three metabolic tests listed below are reported in milligrams per deciliter.
Bilirubin, total: Bilirubin (billy-ru-bin) is a result of the breakdown of red blood cells which are then handled by your liver. If your reds are undergoing their normal process and your liver is fine, your bilirubin level will be within the normal limits. But, if your reds are damaged somehow or if your liver is inflammed, obstructed, or otherwise damaged, the amount of bilirubin is likely to go up because your blood will be hauling the damaged reds off to the liver for processing.
Blood urea nitrogen: This is sometimes also reported simply as urea nitrogen or as BUN. It describes how your kidneys are functioning. This test is less sensitive than the test for creatinine, but taken together, the two tests can help your doctor understand whether your chemotherapy, other treatment, or other disease is having a negative effect on your kidneys.
Creatinine: Creatinine (cree-ah-tuh-neen) is a measure of how your body metabolizes energy. It is produced at a steady rate and depends on the amount of muscle in your body. Larger people will produce more than smaller people. If the amount of muscle in your body changes, the amount of creatinine will change. Creatinine is normally excreted through your kidneys, so this also gives an indication of how well your kidneys are functioning.
Protein tests
The two major protein tests, albumin and total protein are reported in grams per deciliter. Proteins are responsible for many functions in our bodies, including transporting certain molecules to the parts of our bodies where they're needed, regulating certain enzymes that govern our bodies' functions, and as immunologic agents.
Albumin: The levels of albumin are another clue that your oncologist uses to see how your treatment is affecting your body. For example, when you have IVs, become dehydrated, or have decreases in your liver or kidney functions, the amount of albumin circulating in your blood will change.
Total protein: The total amount of protein in your blood will change when you become dehydrated or when your blood becomes hemoconcentrated due to fluid loss for some reason. This is also an indicator of a number of different problems with various organs of your body. So, this test is used together with other tests to monitor your progress.
Enzyme tests
These enzyme tests are reported in units per liter. The various enzymes are present in a variety of situations in your body. Each one is a measure of how well (or poorly) a particular organ or group of organs is functioning.
Alkaline phosphatase: Alkaline phosphatase (alka-leen fos-fuh-taze) is found primarily in the bone and liver and somewhat in the kidney and colon. It is a measure of liver and bone disease and, thus, in some sense is also a tumor marker. If you have new bone that's just forming, (osteoblasts are the cells that do this), this measure will change.
ALT (SGPT): This stands for alanine transaminase (al-a-neen trans-am-in-ase), which is an enzyme present in the liver, with lesser concentrations in the heart, muscle, and kidneys. It is used primarily to diagnose liver disease of various kinds.
AST (SGOT): This stands for aspartate transaminase (ass-par-tate trans-am-in-ase) which is an enzyme present in areas of your body that are metabolizing glucose rapidly. When cells are injured or die, AST is released into the blood stream. Because it measures the presence of damaged cells, it gives your oncologist a clue as to how your treatment is progressing and how it's affecting various parts of your body. Aspartate transaminase is present in your liver, muscles, and lungs, among other organs.
LD: LD is short for lactic acid dehydrogenase (dee-hyd-rog-en-ase). It is an enzyme within your cells that is present especially in the kidneys, liver, brain, lung, heart, reds, and skeletal muscles. It is useful in monitoring the status of the organs in which it is particularly present. It is reported in units per liter.
Lipoprotein tests
Lipoproteins are proteins related to fat in your body.
Cholesterol: This test is the most commonly used indicator of your risk for atherosclerosis and related heart disease. You're likely to have this test on a regular basis, if you had a high value at initial testing. if you're trying to lower your cholesterol by diet, or if you're on a cholesterol-lowering medication. It is reported in milligrams per deciliter.
Triglycerides: This test measures your body's ability to metabolize fats. It, like cholesterol, is a measure of risk for atherosclerosis and related heart disease; but, because triglyceride levels are independent of cholesterol level, doctors often want to know both values to make a better evaluation of risk. Because this test is very sensitive to diet, it is always measured on a fasting basis, i.e., you cannot have had anything to eat or drink (except water) for twelve hours before your blood is drawn for this test.
Lipoprotein electrophoresis: Often determined at the same time as a triglyceride test, this test measures the amounts of the various kinds of lipoproteins in your blood. Two types are most frequently reported:
CEA (carcinoembryonic antigen): This tumor marker is found in about 60 percent of human all breast cancer tumors. The marker is reported in nanograms per milliliter. It is also found in a large percentage of colorectal cancers. It is used as a monitor to follow the effects of chemotherapy and/or surgery. It is NOT a screening test, i.e., it is NOT used to determine whether or not you have cancer..
CA 27.29: This is a relatively new test which replaces the CA15-3 test that many of us have had.
HER-2/neu : This is a monoclonal antibody. It is not commonly found in normal lab tests. However, in order to be treated using Herceptin, you will need to have your her-2/neu level tested based on your original tumor blocks. At this point in time, the laboratories which were involved in the Phase III trial of Herceptin are the ones with lots of experience in this arena. Your her-2/neu value reports you as being an "over-expressor" or not being an over-expressor. Over-expression means that the area of your DNA where this sequence appears has multiple copies, not just a few extra but many, many copies of the sequence of DNA information referred to as her-2/neu. The latest test for HER-2/neu overexpression is called a FISH test (fluorescence in situ hybridization test) which is a DNA probe assay. It is only approved for use in women with primary breast cancer (not metastatic disease) who are node-negative. Approximately 30 percent of patients with breast cancer will be HER-2/neu overexpressors. Something more than 60 percent of patients with inflammatory breast cancer (IBC) will be overexpressors.
Infrequently seen measurement terms
fL = femtoliters (1/1000th of a microliter)
pg = picograms (per cell) for MCH
mml = micromol (1/1000th of a mol -- remember the mol without an "e"
from high school chemistry?)
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