Your blood offers many clues about your heart health. Excessive levels of "bad" cholesterol in your blood, for instance, can be a sign that you're at increased risk of developing life-threatening blockages in your coronary arteries. C-reactive protein (CRP) may indicate whether you're likely to have a heart attack.

Click on the tabs at the left to look at some blood tests you may encounter in the diagnosis, treatment and management of heart disease.

Cardiac enzymes are proteins your body produces to help promote natural biochemical reactions that keep cells functioning normally. Damage to your heart can send excessive levels of cardiac enzymes into your bloodstream. Common tests include:

• Creatine kinase (CK or CPK), which is an enzyme normally found in the brain and in heart and skeletal muscle. There are several subtypes of CK. Your CK levels may signal if you've had a heart attack.
• Lactate dehydrogenase (LDH), which is found in almost all body tissues, including the heart. High levels can indicate a heart attack or other heart damage. This test is only rarely used.
• Troponin, which helps heart muscle contract. Elevated levels of the different types of troponin can indicate whether you've had a heart attack.

C-reactive protein (CRP) is a protein your liver produces as part of your immune system response to injury or infection. It's also produced by muscle cells within the coronary arteries. CRP is a nonspecific sign of inflammation, which means it may not be clear what's causing the inflammation. Inflammation plays a central role in atherosclerosis, in which fatty deposits clog your arteries.

High levels of CRP in your blood may be associated with an increased risk of heart attack, stroke and sudden cardiac death. Some researchers contend that CRP is a better predictor of your heart disease risk than is cholesterol. Although the evidence behind CRP is growing, the American Heart Association doesn't yet recommend CRP screening for the general public — only those at known risk of heart disease.

Cholesterol-lowering statin medications may reduce CRP levels and decrease your cardiovascular risk.

Fibrinogen is a protein in your blood that plays a central role in blood clotting. But too much may promote excessive clumping of platelets, the type of blood cell largely responsible for clotting. That can cause a clot to form in an artery, leading to a heart attack or stroke.

Fibrinogen may also be an indicator of inflammation that accompanies atherosclerosis. It may also aggravate existing injury to artery walls.

Your doctor may check your fibrinogen level if you have an increased risk of cardiovascular disease. Smoking, inactivity, excessive alcohol consumption and supplemental estrogen — whether from birth control pills or hormone therapy — may elevate fibrinogen.

Homocysteine is an amino acid your body uses to make protein and to build and maintain tissue. But excessive levels in your blood may increase your risk of stroke, certain types of heart disease, and disease of the blood vessels of the arms, legs and feet (peripheral artery disease).

Your doctor may check your homocysteine level if you've had cardiovascular problems but don't have any of the traditional risk factors, such as smoking. Your doctor may also advise screening if any family members developed heart problems at a young age or have high homocysteine levels.

Homocysteine levels may drop if you get plenty of folate and B vitamins in your diet through foods such as green, leafy vegetables and fortified grain products or through supplements. But it's not known if reducing your homocysteine level actually reduces your risk of death from cardiovascular disease.

A lipid panel measures the fats (lipids) in your blood. The measurements can indicate your risk of having a heart attack or other heart disease. The panel typically includes:

• Low-density lipoprotein (LDL) cholesterol, the "bad" cholesterol, which promotes accumulation of fatty deposits (plaques) in arteries. These plaques choke off blood supply to the heart and other vital organs.
• High-density lipoprotein (HDL) cholesterol, the "good" cholesterol, which protects against heart disease by helping clear excess cholesterol from your body. This keeps your arteries open and your blood circulating more freely.
• Triglycerides, which help your body store fat and usually reside in the fat tissue, with only low levels in your blood. Higher levels increase your risk of heart disease.
• Total cholesterol, which is the sum of your blood's HDL cholesterol and a portion of triglycerides. Higher levels may put you at greater risk of cardiovascular disease.

Lipoprotein(a) is a type of blood fat (lipid). It's known as Lp(a), or Lp little-a. It forms when a low-density lipoprotein (LDL) cholesterol particle attaches to a specific protein.

The protein that carries Lp(a) may disrupt your body's ability to dissolve blood clots. High levels of Lp(a) may be associated with an increased risk of cardiovascular disease, including early heart disease, heart attack and stroke.

Your doctor may check your Lp(a) level if you or a family member has early-onset coronary artery disease or if you have coronary artery disease but don't have any of the traditional risk factors.

Brain natriuretic peptide, also called B-type natriuretic peptide (BNP), is a protein that your heart and blood vessels produce. BNP acts as a natural diuretic, eliminating fluid, relaxing blood vessels and funneling sodium into the urine.

The BNP concentration in your blood can help in the diagnosis and evaluation of heart failure and other heart conditions. When your heart is failing, your body secretes very high levels of BNP into your bloodstream in an effort to ease the potentially dangerous strain on your heart. BNP levels may also rise if you have new or increasing chest pain (unstable angina) or after a heart attack. BNP levels can also help indicate your treatment progress over time.

A variation of BNP called N-terminal BNP may also be useful in diagnosing heart failure.

Prothrombin is a protein in your blood that helps it clot. The prothrombin test (PT) is one measure of how long it takes your blood to begin clotting. PT tests may be performed differently at the same laboratory or in different labs. Those differences would mean PT measurements aren't standardized and couldn't be compared. To compensate for those differences, results are standardized with the international normalized ratio (INR). This calculation adjusts for variations in normal values of PT tests at different labs.

Prothrombin 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. Clots can block blood vessels, putting you at risk of a heart attack or stroke. Measuring prothrombin time also can help ensure you're getting the right dosage of anticoagulants.