Cyanosis is a symptom of an underlying disease rather than a condition or disease in itself. Cyanosis refers to the bluish discoloration of skin, lips, fingers and toes and mucous membranes.

There are two types of cyanosis – Central and peripheral. In case of peripheral cyanosis there is usually a problem with circulation of the blood in the fingers and toes that turn blue. Some conditions like exposure to cold alone may lead to peripheral cyanosis.

On the other hand central cyanosis usually means a deeper and more serious disease of the heart or lungs. This needs to be evaluated.

Children and infants with central cyanosis that manifests as bluish discoloration around lips, mouth, tongue and oral mucous membrane usually need admission and evaluation.

Diagnosis of an underlying cause includes taking a medical history, a physical examination and so forth. (1-5)

Detailed medical history

The doctor initially will take a detailed medical history. He or she will ask about when the blue coloration developed and if it appeared suddenly or deepened over time.

The physician will ask if the lips, nail beds and tongue are blue or if it is blue all over.

There is enquiry about exposure to cold or sudden visit to a high altitude.

There is enquiry about any poisoning or any intake of drugs. Other symptoms and their intensity and duration is enquired. This includes symptoms such as breathing difficulty, ankle or foot swelling, cough, chest pain etc.

Physical examination

This includes listening to the breathing sounds and heart sounds. The attending physician assesses the blood pressure and strength of the pulse.

If the pulse is weak or the blood pressure is low there may be a circulatory shock. This patient needs to be immediately stabilized with fluids and drugs given via injections and intravenous route before further investigation into the cause of the condition.

Other clinical features include fever (in case of infections), clubbing of fingers, growth retardation in children with cyanotic heart disease etc.

There may be raised jugular venous pressure in the neck. This is seen in patients with heart failure.

Respiratory examination

Respiratory examination shows a poor chest expansion as is seen in asthma and chronic bronchitis.

The chest on percussion (a special test using fingers that are tapped gently over the test) emits a dull sound in cases of pneumonia and pleural effusion. There are sounds of crepitation over the lungs.

Cardiovascular examination

Cardiovascular examination shows abnormal heart sounds. There may be murmurs and other sounds signifying heart defects.

Tests for cyanosis

Tests are performed to assess the situation. These include the following:

• The commonest test is the Arterial blood gas analysis and Blood oxygen saturation by pulse oximetry. These tests are performed to assess the amount of oxygen in the arterial blood.

• A complete blood count is prescribed. This helps detect features like a low Red blood cell count (anemia), low haemoglobin (anemia) or high RBC count (polycythemia) etc. High counts of white blood cells are indicative of infections.
• A chest X ray may be suggested to detect lung pathologies like pleural effusion etc.
• ECG or Electrocardiogram is recommended to detect abnormalities of the heart rhythm and rate.

Type of abnormality or defect of the heart in congenital heart defects can be detected by imaging tests such as:

• • Echo cardiography,
  • Transesophageal echocardiogram (TEE),
  • Cardiac Doppler with Echo or Ultrasound,
  • Cardiac or chest CT scan and MRI scan.

Echocardiography may be used to look inside the heart to detect the structural defect. Doppler helps detect the adequate direction and amount of blood flow across the heart and the large vessels.

• Cardiac catheterisation gives information about exactly how the blood is being pumped through the heart. This involves insertion of a small flexible tube, called a catheter into a blood vessel in the arm or groin. The tube is threaded up to the heart.

The end of the tube has a small blood pressure monitor, which can be used to take blood pressure readings in different parts of the heart. Further a colored dye is used to see the movement of blood through the heart.

• Other tests for heart defects include Nuclear imaging tests and cardiac Electrophysiologic study (EPS).
• In pneumonia and lung infections sputum is tested for microorganisms. Blood cultures for infection may also be prescribed.
• Ventilation-perfusion scan is recommended in patients with pulmonary embolism. A lung angiography helps to visualize the blood vessels of the lungs and is helpful in detection of the embolism
• If methemoglobin or sulfhemoglobin is suspected a Haemoglobin spectroscopy is prescribed.
• For detection of arterial occlusion a Digital subtraction angiography may be prescribed. Similarly a Duplex Doppler or venography is prescribed for acute venous occlusion.