What blood tests are done in suspected CHD? 

Blood tests in suspected Congenital Heart Disease (CHD) are primarily used to measure heart stress, assess oxygen levels, and identify underlying genetic conditions. While imaging like an echocardiogram provides the definitive structural diagnosis, blood tests such as B-type natriuretic peptide (BNP) help clinicians quantify the strain on the heart muscle. Additionally, arterial blood gases are used to measure the exact concentration of oxygen and carbon dioxide in the bloodstream, which is critical for babies with cyanotic defects. 

In clinical practice, blood tests act as a supportive tool alongside physical examinations and pulse oximetry. For newborns and infants, these tests can differentiate between heart failure and respiratory infections. For adults with CHD, regular blood monitoring is essential to track the impact of the defect on other organs, such as the kidneys and liver, and to monitor the effectiveness of medications like diuretics or anticoagulants. 

What We’ll Discuss in This Article 

• Markers of heart stress and failure, specifically BNP and NT-proBNP. 

• The role of blood gases in measuring oxygenation and pH levels. 

• Complete blood counts and their importance in detecting anaemia. 

• Genetic and chromosomal blood testing for associated syndromes. 

• Emerging 2024-2025 research on neonatal dried blood spot biomarkers. 

• Pre-operative blood panels used to ensure surgical safety. 

Heart Stress Markers: BNP and Troponin 

The most significant blood tests for evaluating heart function in suspected CHD are natriuretic peptides. When the heart chambers are stretched or under pressure due to a defect—such as a large hole or a narrow valve—the heart muscle releases a protein called B-type natriuretic peptide (BNP). High levels of BNP or its more stable counterpart, NT-proBNP, provide a clear indication that the heart is struggling to pump efficiently. 

While BNP measures stress, troponin tests are used to detect actual injury to the heart muscle. Although more common in adult heart attacks, troponin levels can be elevated in infants with severe CHD or those experiencing myocarditis (inflammation of the heart muscle). According to the European Heart Journal, Guo, H., et al. (2025). ‘First trimester maternal infections and offspring congenital heart defects: a meta-analysis.’  maternal infections in the first trimester increase the risk of these structural defects, often necessitating the early use of these biomarkers to monitor neonatal cardiac stability. 

Oxygenation and Metabolic Blood Tests 

For babies who appear ‘blue’ (cyanotic) or have low oxygen readings on a pulse oximeter, an arterial blood gas (ABG) test is often performed. This test involves taking a small sample of blood from an artery to measure the exact partial pressure of oxygen (PaO_{2}) and carbon dioxide (PaCO_{2}). This is far more accurate than skin-based sensors and helps clinicians determine if the low oxygen is caused by a heart defect or a lung problem. 

The table below summarizes common blood tests used in the diagnostic workup for CHD: 

Test Name	What it Measures	Clinical Significance in CHD
BNP / NT-proBNP	Heart wall stress protein	Detects heart failure and pumping strain.
Blood Gases (ABG)	Oxygen, $CO_{2}$, and pH	Assesses the severity of ‘blue’ heart defects.
Complete Blood Count	Red/white cells & platelets	Checks for anaemia, which worsens heart strain.
Electrolytes	Sodium, Potassium, Calcium	Monitors the effects of ‘water pills’ (diuretics).
CRP / Procalcitonin	Inflammatory markers	Helps rule out infection as a cause of distress.
Genetic Karyotype	Chromosomal structure	Identifies conditions like Down’s or DiGeorge.

Genetic and Chromosomal Analysis 

Because approximately 20% to 30% of CHD cases are linked to genetic conditions, blood-based genetic testing is a standard part of the diagnostic process. If a baby is born with a heart defect and other physical features, clinicians may order a ‘karyotype’ or ‘microarray’ test. These tests look for extra or missing pieces of DNA that could explain the heart’s malformation. 

• Down’s Syndrome (Trisomy 21): Frequently associated with Atrioventricular Septal Defects (AVSD). 

• DiGeorge Syndrome (22q11.2 deletion): Strongly linked to conotruncal defects like Tetralogy of Fallot. 

• Turner Syndrome: Often involves a narrowing of the aorta (coarctation). 

Identifying a genetic cause is vital because it helps the medical team look for other associated health issues and provides parents with information regarding the risk of CHD in future pregnancies. 

Cutting-Edge Data: Neonatal Biomarker Screening 

New research from late 2024 has introduced the possibility of using ‘dried blood spot’ (DBS) samples similar to the standard ‘heel prick’ test to screen for CHD. By measuring a combination of NT-proBNP and a protein called IL-1 RL1 in just 3 \mu L of blood, scientists have achieved a 95% accuracy rate in identifying high-risk CHD cases that were missed by pulse oximetry or prenatal scans. This emerging technology could lead to earlier diagnoses for asymptomatic babies who might otherwise be discharged from the hospital without detection. 

Conclusion 

Blood tests for suspected CHD provide essential data on how well the heart is coping with a structural defect. From measuring heart stress with BNP to assessing blood gases for oxygen levels, these tests guide the clinical team in planning treatment and surgery. While no single blood test can ‘diagnose’ CHD on its own, they are indispensable for monitoring heart failure and identifying genetic triggers. The recent findings in the European Heart Journal emphasize that early laboratory testing is increasingly important for children born following first trimester maternal exposures. 

If your baby shows signs of a heart problem, such as blue-tinted skin, rapid breathing, or excessive sweating during feeding, call 999 immediately. 

If you notice a sudden worsening of breathlessness or a blue tinge to the lips and nails in an older child or adult, call 999 immediately. 

Authority Snapshot (E-E-A-T Block) 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician (MBBS) with postgraduate certifications in ACLS and BLS. Dr. Petrov has extensive clinical experience in general medicine and emergency care, having worked in hospital wards and intensive care units where blood markers like BNP and blood gases are vital for cardiac assessment. His expertise ensures this information on CHD blood testing is accurate, safe, and aligned with current NHS and NICE clinical standards.