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Blood tests: Seeking clues about your heart’s health
Your blood offers many clues about your health. It can indicate, for instance, whether you're having a heart attack or if you're likely to have one down the road. If your doctor suspects you have a heart problem or that you might be at increased risk of heart disease, your blood is one of the first places to start searching for early indications of trouble. That's because the presence or absence of certain substances in your blood can reveal a problem. Excess "bad" cholesterol, for instance, can alert you and your doctor that you could be at risk of developing life-threatening blockages (plaques) in your coronary arteries. And if a particular enzyme appears in your blood, it might indicate that you're in the midst of having a heart attack. Here's a look at some specialized blood tests that might be ordered to help predict or detect heart problems. Some can be done in your doctor's office, while others might be done in a lab or even the emergency room, depending on your situation.
BNP levelSevere shortness of breath — air hunger — is often the main symptom of heart failure. But difficulty breathing can also be a symptom of other problems, such as emphysema and pneumonia. A simple, rapid test to check the concentration of BNP in your blood can help doctors quickly determine what's really causing your symptoms. BNP, or B-type natriuretic peptide, is a protein your heart and blood vessels naturally produce. BNP acts as a diuretic, eliminating fluid, relaxing vessels and funneling sodium into the urine. When you're in heart failure, though, very high levels of BNP are secreted into your blood in an effort to ease the potentially dangerous strain on your heart. The BNP concentration can even offer some evidence of how severe your heart failure might be. Check with your doctor about normal ranges for your situation. C-reactive proteinA simple and inexpensive blood test to detect inflammation within your blood vessels may indicate whether you're at increased risk of developing heart disease. A protein called C-reactive protein (CRP) is produced by the liver as part of a normal immune system response to injury or infection. High levels of CRP in the blood also have been associated with an increased risk of cardiovascular disease, including heart attack and stroke. In fact, some researchers say that CRP is a better predictor of your risk of heart disease than cholesterol levels are. If your cholesterol is low but your CRP is high, evidence shows you're at an increased risk. CRP alone, however, isn't enough to predict your risk of heart disease. In addition, a very high level CRP probably isn't related to blood vessel disease. That's because your CRP level can be elevated by other conditions, such as connective tissue diseases, or infections, such as gingivitis or a urinary tract infection. And CRP's role in heart disease isn't yet clear. Researchers think that buildups of cholesterol and fatty material (plaques) that line the blood vessels can become inflamed as the body sends in white blood cells to fight what it thinks is infection. As the inflammation increases, it can cause plaques inside the arteries to rupture. Blood clots then form on the ruptured plaque, blocking the vessel and cutting off blood supply to the heart or brain, causing a heart attack or stroke. Guidelines issued jointly by the American Heart Association and the Centers for Disease Control and Prevention in January 2003 suggest whose CRP level should be checked. The CRP test shouldn't be used as a standard screening tool for the general public. And if you've already got heart disease, or are at a very high risk of developing it, you don't need the test, either, because you should be getting standard treatment anyway. Rather, the test is recommended only if you have an intermediate risk of developing coronary heart disease in the next 10 years. The test can help your doctor decide on further evaluations or whether you need more aggressive therapy to help prevent cardiovascular disease. To test for CRP, blood is drawn with a simple, inexpensive finger-prick test or from a vein. Testing is generally done twice, two weeks apart. C-reactive protein is measured in milligrams per liter (mg/L) of blood. What the results indicate:
If your CRP is greater than 10mg/L, the result is likely due to an infection or other condition. In that case, the test should be repeated in the future to assess cardiovascular risk. The guidelines recommend that the CRP test be used only in conjunction with assessments of known risk factors, such as cholesterol levels. Cardiac enzymesEnzymes are proteins your body produces to help promote chemical reactions. Low levels are normally present in your bloodstream. But when the levels become elevated, it can be a sign that your body has suffered damage of some sort, such as heart muscle damage. Doctors commonly order a blood sample to measure the enzymes specific to your heart (cardiac enzymes) if you have chest pain or might be having a heart attack, or to check for heart damage after surgery. Common cardiac enzymes analyzed:
Because the normal ranges for these enzymes often vary by lab, as well as by age and sex, check with your doctor for the values that apply to your specific situation. Lipid panelA lipid panel usually includes four measurements: three types of fats (lipids) in your blood, plus a total: Low-density lipoprotein (LDL) cholesterol. This is sometimes called the "bad" cholesterol because too much of it in your blood causes an accumulation of plaques in your arteries (atherosclerosis), leading to heart disease. High-density lipoprotein (HDL) cholesterol. This is sometimes called the "good" cholesterol because it can carry away LDL cholesterol, helping keep arteries open and your blood running more freely. Triglycerides. These lipids help your body store fat and are usually found in the fat tissue, with only low levels in your blood. Total cholesterol. This is the sum of your blood's cholesterol content. Together, the four numbers can provide clues about your risk of having a heart attack. Although these lipids are necessary for your body to function normally, the kind and amount present in your blood might indicate if you're at increased risk of developing heart disease.
If your numbers are anything but optimal, talk to your doctor about making changes in your diet and lifestyle or taking medications. Oxygen levelThe amount of oxygen in your blood (oxygen saturation) can also be telling. Normally, blood in the arteries picks up oxygen in the lungs, so it's rich in oxygen to then distribute to the rest of your body. Once depleted of oxygen, the blood flows back to your heart and lungs through veins. An imbalance in oxygen saturation can indicate that your heart or lungs aren't functioning normally. To check your oxygen saturation, a small device called a pulse oximeter can be painlessly clipped to the end of a finger or to the earlobe. If more precise information is necessary, the oxygen saturation can be measured in blood drawn from your radial artery, which is located on the inside of your wrist below the thumb. Local anesthetic can be used to numb the area first. Abnormally low results might indicate that your body isn't getting enough oxygen. Because the normal ranges can vary by lab, as well as by age and sex, check with your doctor for the optimal values for your specific situation. Prothrombin timeProthrombin is a plasma protein in your blood that helps it clot. The prothrombin test is one measure of how long it takes your blood to begin clotting. This measurement is important if you're taking blood-thinning medications (anticoagulants) or have a medical condition that could cause problems with clotting. If you have an abnormal heart rhythm (atrial fibrillation) or deep vein thrombosis, or you've had a heart valve replaced, your blood is more likely to form clots. And clots can block blood vessels, putting you at risk of a heart attack or stroke. The result of the prothrombin test is usually reported as an international normalized ratio (INR) in which 1.0 is the normal value if you're not taking anticoagulants. Talk to your doctor about the appropriate INR for your situation because it can vary by lab. And if you're taking anticoagulants, talk to your doctor about how frequently you'll need testing. The prothrombin time can help ensure you're getting the right dosage of medication. Special preparationsMany of these blood tests require fasting overnight for the greatest accuracy. Some require you to restrict fat or alcohol in your diet before the test. In addition, medications, herbs or supplements might skew the results. Talk to your doctor about any special preparations to make before you have such tests. And remember, blood tests alone usually aren't enough to make an accurate diagnosis or rule out a condition. In many cases you might need other tests to check the health of your heart and cardiovascular system, such as chest X-rays, echocardiography or an electrocardiogram, for instance.
Dry Skin (xerosis)
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Creatine kinase (CK or
CPK). Creatine kinase (CRE-uh-tin KI-nase) is an enzyme normally found in the brain, heart and skeletal muscle. Levels begin to rise within 4 to 6 hours of a heart attack, peak in 18 to 24 hours, and return to normal in a few days. Your doctor might repeat the test several times to detect a pattern. 