Cyanosis: Differential Diagnosis, History, Examination

The Cyanosis is the abnormal bluish or purple discoloration of the skin and/or mucous membranes due to reduced hemoglobin in the blood (less than 5 g/dL). We are going to put differential diagnosis of Cyanosis, then discuss History, Examination and Investigations.

Cyanosis is of two types: Central and Peripheral. Central occurs due to poor oxygenation in lungs while Peripheral occurs due to inadequate or obstructed circulation.

Differential Diagnosis


  1. Severe respiratory disease
  2. Pulmonary edema
  3. Pulmonary embolism
  4. Congenital cyanotic heart disease


  1. Methaemoglobinaemia
  2. Sulphaemoglobinaemia
  3. All causes of central cyanosis
  4. Cold exposure
  5. Raynaud’s phenomenon
  6. Arterial occlusion
  7. Venous occlusion
  8. Acrocyanosis


Central cyanosis


Cyanosis due to congenital heart disease causing anatomical right to left shunts may have been present from birth or the first few years of life. Immediate onset may be due to pulmonary emboli or cardiac failure. Acute onset may be precipitated by pneumonia and asthma. Patients with COPD develop it over many years. Accompanying polycythemia may exacerbate it in these patients.

Chest pain

Cyanosis associated with pleuritic chest pain may be due to pulmonary emboli or pneumonia. Dull, aching chest tightness is experienced by patients who develop it from pulmonary edema as a complication of myocardial infarction.


Sudden onset of dyspnea can occur with pulmonary emboli and pulmonary edema, while conditions such as asthma may produce a more gradual onset.

Past medical history and drug history

Any co-existing respiratory disease is significant, as it can result from any lung disease of sufficient severity. Consumption of drugs such as phenacetin and sulphonamides may precipitate methaemoglobinaemia and sulphaemoglobinaemia, respectively.

Peripheral cyanosis

General history

Acrocyanosis is a condition in which the hands are persistently blue and cold; it is not associated with pain. Raynaud’s phenomenon is the episodic three-color change that occurs, with arterial vasospasm (white), cyanosis (blue) and reactive hyperemia (red). It may be idiopathic or be associated with connective tissue diseases, and drugs such as beta blockers.

Peripheral type may also result from acute arterial occlusion and is accompanied by pain and mottling of the skin. Iliofemoral deep venous thrombosis can produce a painful blue leg, termed phlegmasia cerulea dolens.



Pneumonia and pulmonary emboli may be associated with pyrexia.


It is often difficult to detect minor degrees of it cyanosis. Central type produces a blue discoloration of the mucous membranes and digits; peripheral type produces blue discoloration only of the digits. Episodic peripheral type may be due to Raynaud’s disease and this may be associated with small areas of infarction on the fingertips.

The presence of clubbing may be due to congenital cyanotic heart disease. Classically, patients with chronic bronchitis appear cyanosed with a poorly expanding barreled chest. The JVP is elevated with congestive cardiac failure.

Respiratory examination

Poor chest expansion occurs with chronic bronchitis and asthma. Unilateral impairment of expansion may occur with lobar pneumonia; in addition, dullness to percussion is experienced over the area of consolidation. Localized crepitation may be auscultated with lobar pneumonia, but is more widespread with bronchopneumonia, pulmonary edema and chronic bronchitis.

Air entry is poor with chronic bronchitis and asthma. Bronchial breathing may be auscultated over an area of consolidation, and additional sounds such as wheezing may be heard with asthma.

General Investigations

Oxygen saturation

Saturation is usually below 85%


Decreased pO2 all severe lung disease


Hb increased chronic cyanosis. WCC increased pneumonia and pulmonary embolism


Features of myocardial infarction. Non-specific abnormalities with pulmonary emboli


Pneumonia, pulmonary infarct, cardiac failure

Specific Investigations

Sputum and Blood cultures


V/Q scan or CT pulmonary angiography

Pulmonary embolus


Cardiac failure

Hb spectroscopy

Methaemoglobinaemia, sulphaemoglobinaemia

Digital subtraction angiography

Acute arterial occlusion

Duplex Doppler or venography

Acute venous occlusion

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