Important blood tests in relation to the heart – Cardiology Basics

Important blood tests in relation to the heart – Cardiology Basics

Here are some important blood tests in relation to the heart. Normal ranges of some of these tests may vary between labs.
Cholesterol is a type of fat found in the blood and has a role in the development of atherosclerosis in the coronary arteries as well as other arteries. Desirable value of total cholesterol in blood is less than 200 milligrams per decilitre.

Triglycerides is another type of fat found in the blood. Desirable value is less than 150 milligrams per decilitre. Very high levels of triglycerides carry a risk of pancreatitis. Calorie restriction is important in reducing triglyceride levels in addition to fat restriction. This is because excess calories, typically carbohydrates, get converted to triglycerides in the body.

HDL cholesterol or high density lipoprotein cholesterol is called good cholesterol as it is involved in reverse cholesterol transport from the blood vessels to the liver. It is nice to have HDL cholesterol above 60 milligrams per decilitre. HDL levels can be increased by regular exercise programs. Pharmacological approaches to increase HDL have not be useful so far. Higher values of HDL cholesterol are better for you, though there is a concern that extremely high values could be deleterious.

LDL cholesterol or low density lipoprotein cholesterol is called bad cholesterol. Excess LDL cholesterol in blood can lead to atherosclerosis in the important arteries and lead to stroke and myocardial infarction. LDL levels can be reduced by diet control, regular exercise and medications if needed. Statins are the most commonly used medications to lower LDL cholesterol.

PCSK9 inhibitors are a more powerful, but expensive option, especially in those who cannot tolerate statins or are unable to achieve target levels with statins. Generally, the desirable LDL level is below 100 milligrams per decilitre, though lower values are recommended for those with coronary artery disease. VLDL cholesterol or very low density lipoprotein cholesterol is another form of bad cholesterol.

The importance of getting lipid profile estimated in the fasting state is coming down. But if it is for triglyceride levels, postprandial increase in triglycerides have to be kept in mind. Yet, there is also some indication that an undue postprandial rise in triglyceride levels also conveys a risk for cardiovascular disease.

Creatine phosphokinase–MB (CPK-MB) is a cardiac marker used for the diagnosis of myocardial infarction. It is an enzyme released from the myocardium on damage. Though currently troponins are the sheet anchor for the diagnosis of myocardial infarction, they cannot be used for detection of early re-infarction due to persistence in blood for a longer period. In such a situation CPK-MB is still useful. CPK-MB though relatively specific for heart muscle injury, it can be elevated in massive skeletal muscle injury.

Cardiac troponins are proteins released from the myocardium after damage. It is the most important blood test used for detection of a myocardial infarction. Delta troponin or serial rise in high sensitivity troponin level over a period of one or two hours have been useful in detecting myocardial infarction in the usual window period before six hours needed for a regular troponin rise. For using delta troponin, we need the lab normal ranges for the interval at which it is being estimated.

Troponin elevation without supporting evidence of myocardial infarction is designated as myocardial injury and can occur in a large number of conditions like burns and renal failure. Earlier these were considered as false positives. Though there is no role for cardiac interventions in these cases, prognosis of troponin elevation in myocardial injury is equally bad if not worse than myocardial infarction.

BNP and NT-ProBNP are blood tests used for detection of heart failure in the emergency department. NT-proBNP is used more often than BNP with a shorter half-life. Natriuretic peptides are useful in diagnosis as well as prognosis evaluation. Levels can be unduly high in chronic kidney disease.

Angiotensin II Receptor Blocker Neprilysin Inhibitor (ARNI) use is another situation which can alter BNP levels, but not NT-proBNP levels. This is because BNP degradation is prevented by ARNI and levels rise, though one would have expected a fall due to improvement in heart failure [1].

C-reactive protein or CRP is a predictor for risk of cardiovascular disease. Risk increases as the value rises. According to the American Heart Association levels of high sensitivity CRP lower than 1.0 mg/dl indicate low risk of developing cardiovascular disease while levels higher than 3.0 mg/dl indicates high risk. The risk is moderate with levels in between. Predictive value of hs-CRP is independent of LDL levels and addresses the inflammatory component of cardiovascular risk.

Elevated Antistreptolysin O (ASO) titer indicates recent streptococcal infection. It is a supportive test in the diagnosis of rheumatic fever, not a diagnostic one. But associated clinical or echocardiographic evidence is needed for the diagnosis of rheumatic fever. It may be noted that even in an epidemic of streptococcal sore throat, only about 3% will develop rheumatic fever, while the remaining persons will also have elevated ASO titre! Usually, ASO elevation will not be there in chorea and indolent carditis, which are also major manifestations of rheumatic fever.

Reference

1. Myhre PL, Vaduganathan M, Claggett B, Packer M, Desai AS, Rouleau JL, Zile MR, Swedberg K, Lefkowitz M, Shi V, McMurray JJV, Solomon SD. B-Type Natriuretic Peptide During Treatment With Sacubitril/Valsartan: The PARADIGM-HF Trial. J Am Coll Cardiol. 2019 Mar 26;73(11):1264-1272.