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Blood tests help doctors review your chemical make-up
Published: Wednesday, February 09, 2011, 12:03 AM
Blood carries many secrets about our health. Pumped by the heart and circulated through your body, blood supplies tissues and organs with vital nutrients and oxygen and, at the same time, draws toxins and waste products for disposal.
By testing your blood, a doctor can review the chemical make-up of your system, evaluate how well your organs are working, diagnose diseases, learn whether you have risk factors for heart disease or monitor your response to medications.
Interestingly, although blood tests are an excellent diagnostic tool, many adults don’t understand why they are done. Among the respondents in a statewide poll conducted by the Pennsylvania Medical Society’s Institute for Good Medicine, nearly 60 percent of those who had blood work did not know what it was for.
To help demystify blood tests, we interviewed Dr. Kathryn M. Frantz of Susquehanna Internal Medicine Associates in Camp Hill and Judy Darr, PinnacleHealth’s laboratory administrative director, to summarize the most common blood tests, why they are given and what the results can prove.
Comprehensive Metabolic Panel (CMP)
What is it?
This is the No. 1 test in reviewing the body’s chemistry, as well as the status of the kidneys and liver.
What does it measure?
BUN (blood urea nitrogen) and creatinine are waste products that are filtered out of the blood by the kidneys and are indicators of kidney function. Increased levels might point to a kidney problem. High creatinine might indicate the possible malfunction or failure of the kidneys.
Enzymes are found in the liver and other tissues. Bilirubin is a waste product of the liver. High levels of any of these indicate dysfunction, disease or inflammation.
Calcium guards against osteoporosis. Abnormal levels might be a sign of kidney problems, bone or thyroid disease, cancer, malnutrition or other disorders.
Glucose is the type of sugar your body uses for energy. Abnormal levels might indicate diabetes.
Electrolytes are the minerals that help maintain fluid levels and acid-base balance in the body. They include potassium, sodium, CO2 (bicarbonate and carbon dioxide) and chloride. Electrolyte imbalance can be present with a wide range of acute and chronic illnesses.
Why is it given?
It’s given to patients who take Lipitor or another medication that might affect the liver, or to patients who take medicines that might affect the kidneys, such as diuretics (commonly known as water pills), blood pressure pills or antidepressants. It’s often part of an overall physical check-up for adults who have not had recent blood work. According to Frantz, every one of the components revealed in the CMP relates to a medical issue. The Basic Metabolic Panel (BMP), is similar to the CMP, but does not include liver function results.
Complete Blood Count (CBC)
What is it?
The CBC is a common test that gives your doctor a baseline measurement of the concentration of white blood cells, red blood cells and platelets in your blood. If the cell populations are within normal limits, you might not require another CBC until your health status changes or your doctor feels that it is necessary.
What does it measure?
A CBC reveals the number of your cells, information on the distribution of white cells, the size of red cells and a statistical analysis of those cells.
Why is it given?
Symptoms or medical problems such as fatigue, shortness of breath, belly pain, chest pain, arthritis or previous anemia often merit a CBC in order to give a proper diagnosis. Also, it’s given if you have other diseases such as malaria, leukemia, sickle cell anemia or are awaiting surgery. Significant increases in white blood cells might help confirm an infection. A decrease in the number of red blood cells (anemia) might indicate a problem or loss of these cells. A platelet count that is low or extremely high also can be a sign of a bone marrow disease such as leukemia. .
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Lipid Screen or Lipid Panel
What is it?
It screens the cholesterol levels in your body.
What does it measure?
HDL — High-density lipoproteins or “good” cholesterol. It takes cholesterol away from cells and transports it to the liver for removal.
LDL — Low-density lipoproteins or “bad” cholesterol. It contains the greatest percentage of cholesterol and deposits it on artery walls.
Triglycerides — Fat in the blood responsible for providing energy to cells.
Why is it given?
Patients at risk for coronary heart disease, hypertension or diabetes receive the test. Elevated cholesterol is associated with an increased risk of heart disease. Fasting is generally required for the test.
Hemoglobin A1c
What is it?
Routinely given to diabetics or those whose sugar is borderline. The test monitors the patient’s glucose control over time.
The test provides a picture of the average amount of glucose in the blood over the last few months, which helps the doctor and diabetic patient determine if the measures being taken to control this disease are working or need adjustment.
Why is it given?
Diabetics need to keep their blood glucose levels close to normal, and this helps minimize the complications caused by chronically elevated levels. Fasting before the test is often required.
Thyroid Stimulating Hormone (TSH) Test
What is it?
The TSH test is most often used as a screening test for fatigue, weight gain, weight loss, anxiety, severe diarrhea or constipation.
What does it measure?
The test measures the levels of TSH, a hormone made and released by the pituitary gland. The pituitary can sense whether there is enough thyroid hormone in the bloodstream and releases TSH when it detects insufficient thyroid hormone.
Why is it given?
It helps diagnose a thyroid condition, such as hypothyroidism or hyperthyroidism.
Prothrombin Time (P-TIME)
What is it?
It’s a test that measures how quickly your blood clots.
What does it measure?
Prothrombin is a protein produced by the liver that aids in your blood clotting. During this process, prothrombin turns into thrombin. The P-Time test measures the time it takes for this to occur.
Why is it given?
It’s used to check for bleeding problems, especially if you are going to have surgery or are taking a blood-thinning medication. Patients taking these medicines might have the P-Time done frequently to monitor the medication’s effectiveness.
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Dr. Jeff Hersh: Understanding blood tests
By Dr. Jeff Hersh.
GateHouse News Service
Posted Feb 08, 2011 @ 12:11 PM
Q: I had a routine blood test, and my doctor told me my white blood cell count was low. Should I be worried?
A: Several different types of white blood cells fight bacterial, fungal, viral and/or parasitic infections, as well as serving other functions. In adults, a white blood cell count less than 3,500 cells per microliter is considered low; the normal threshold in children varies with age.
White blood cells are made in the bone marrow and are released into the blood stream. They then circulate in the blood stream or take up residence in the vascular endothelium system or certain body tissues/organs. Old white blood cells are cleared from the blood stream by the spleen and liver.
The white blood cell count is measured by evaluating the concentration of white blood cells in the bloodstream. Falsely low measurements can occur due to clumping of the white blood cells or from other factors.
A truly low white blood cell count can be from a congenital cause or it can be acquired. There are many different congenital conditions that cause low white blood cell counts. An acquired low white blood cell count can be due to:
Decreased bone marrow production: This may be due to infections (viral infections are the most common cause), medication reactions (the second most common cause), certain congenital conditions, medication effects (such as from chemotherapy agents) or from cancer/infections/other conditions that infiltrate the bone marrow "crowding out' its ability to produce normal white blood cells. In addition, certain autoimmune conditions can affect the hormones that trigger white blood cell production, hence "turning off the switch" that tells the bone marrow to produce white blood cells. There are also many conditions that may directly affect the cells that make the white blood cells, causing ineffective production of normally functioning cells. High thyroid levels and/or certain vitamin or mineral deficiencies (such as B-12 or folate deficiencies) can cause inadequate white blood cell production as well.
Increased destruction of white blood cells in the bloodstream: This may be due to autoimmune conditions (possibly triggered by medication reactions) or many other conditions.
Increased clearance of white blood cells (even normally functioning ones): This may be due to an enlarged spleen (from whatever cause).
Using them up faster than they can be replaced: Overwhelming infections can do this.
Migration of the cells out of the bloodstream: In some conditions white blood cells can migrate to the vascular endothelium or other tissue pools/organs.
The type, risk and severity of any clinical problem from low white blood cells depends on the type of white blood cells that are affected and how severe the deficit is. Many of the conditions that cause a low white blood cell count are benign, causing minimal or no clinical problems. However, since white blood cells are one of the main ways the body fights infections, a low white blood cell count can lead to an increased risk of infection.
Polymorphonuclear cells (PMNs) are the most common type of white blood cells and, hence, low white blood cells almost always implies a low PMN count. Since PMNs fight bacterial infections, overall this is the most common infection from low white blood cells.
Low white blood cell count is more common in African Americans; 5 percent to 10 percent of black Americans have low neutrophil counts, as opposed to less than 1 percent of white Americans. Thankfully, this is usually due to a benign inherited condition, so most of these patients do not have clinical problems.
In patients with a mildly decreased white blood cell count noted on a routine blood test who do not have a history of infections, other testing may not be required. However, in patients with a history of infections, or those with other concerning results of their blood test, other testing may be indicated.
For example, if transient neutropenia is suspected (a condition where a patient's PMNs drop for several days every few weeks, predisposing them to infection) blood tests to check their white blood cell count may be required several times per week for several weeks. If decreased cell production is suspected, a bone marrow biopsy may be required. If an autoimmune condition is suspected screening tests for a collagen vascular disease or other testing may be needed. If a chronic infection is suspected -- for example, HIV infection -- other tests may be indicated.
Many patients with low white blood cells do not require treatment. However, good dental care (since this can be a source of infection) and increased vigilance when they have a fever or appear ill is indicated.
Depending on the cause of the low white blood cells, some patients may benefit from antibiotics to minimize their risk of acquiring an infection. For example, certain HIV patients are put on specific types of antibiotics.
For some patients -- like those receiving chemotherapy for certain cancers -- medications that stimulate the bone marrow to increase production of white blood cells may be beneficial.
A low white blood cell count should trigger a discussion with your health care provider. He or she can evaluate your history and risk factors, as well as the other details of the test results, and determine what other testing and/or treatments may be required.
Jeff Hersh, Ph.D., M.D., F.A.A.P., F.A.C.P., F.A.A.E.P., can be reached at DrHersh@juno.com.
MetroWest (Mass.) Daily News
Copyright 2011 The Milford Daily News.
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