What is the Difference Between ABG CBG and VBG

The key difference between ABG CBG and VBG is that ABG test uses blood drawn from an artery while CBG test uses blood drawn from capillaries, and VBG test uses blood drawn from a vein.

Blood gas analyses are done in order to assess levels of oxygen and carbon dioxide, acid-base balance, and efficiency of lungs. ABG, CBG, and VBG are three types of tests done for a common purpose. ABG stands for arterial blood gas while CBG stands for capillary blood gas, and VBG stands for venous blood gas. Out of the three test types, ABG is the most effective test. However, due to certain conditions of patients (severity and age), CBG and VBG are performed as alternate methods.

CONTENTS

1. Overview and Key Difference
2. What is ABG
3. What is CBG 
4. What is VBG
5. Similarities – ABG CBG and VBG
6. ABG vs CBG vs VBG in Tabular Form
7. Summary – ABG vs CBG vs VBG

What is ABG?

ABG or arterial blood gas is a test that measures the different parameters of blood moving along an artery. In a healthy individual, when the blood moves, passing through the lungs, oxygen moves into the blood, and carbon dioxide moves out of the blood effectively. ABG test provides a quantitative and qualitative measurement for the effectiveness of lungs to transport oxygen into the blood and remove carbon dioxide from the blood. An ABG test measures partial pressure of oxygen, partial pressure of carbon dioxide, pH, bicarbonate, oxygen content, and oxygen saturation.

Figure 01:  Impact of ABG

This test is done in order to assess different illnesses associated with lungs and breathing. ABG test is mainly done to check severe breathing difficulties and lung diseases. These diseases include cystic fibrosis, asthma, and COPD (chronic obstructive pulmonary disease). Apart from this, ABG test can assess the level of functioning of the lung, requirement of additional oxygen and measure the acid-base level of blood of patients with kidney failure, heart failure, and uncontrolled diabetes. ABG test is done by drawing blood from an artery, usually from the radial artery (inside of the wrist). But the femoral artery and the brachial artery are also used to draw blood to conduct the test.

What is CBG?

CBG or capillary blood gas is a test performed in infants or kids and elderly patients with fragile veins. This test asses parameters such as oxygen, carbon dioxide, and acid-base balance. CBG is an alternative test to ABG and is performed only when sampling is difficult, especially in neonates, infants, small kids, and elderly patients with fragile veins. Severe respiratory disorders that occur in such groups of individuals need to be treated immediately in order to prevent complications. Hence, capillary blood gas test is a vital method practiced at different medical institutes.

Figure 02: Capillary Blood Gas Exchange

During this test, blood is drawn by puncturing the cutaneous layer of the skin at a place of high vascularization. Usually, before the test, the vascularized area is warmed up to dilate the blood vessels and to accelerate the blood flow. This also reduces the difference between arterial and veinous gas pressures. CBG test is done due to several reasons. These include unavailability of venous or arterial access for blood gas analysis, abnormal readings of transcutaneous oxygen values, end-tidal carbon dioxide values, pulse oximetry values. In addition, CBG is done to minimize multiple arterial and venous blood drawing from infants, to avoid ventral or arterial access and thereby reduce the risk of infection. CBG test consists of several rare complications such as infection, nerve damage, haematoma, skin breakdown, and bone calcification.

What is VBG?

VBG or venous blood gas is a traditional test performed to analyze ventilation conditions and blood acid-base balance. This is done as an alternative method to arterial blood gas (ABG) test when the individual has diminished pulses due to poor peripheral blood circulation or low blood pressure. At normal levels, VBG test is performed with a venous blood sample drawn by vein puncture.

VBG is a convenient test, especially in intensive care units since patients already have a central venous catheter. Instead of the central venous blood sample, VBG test is performed by peripheral venous sample (by peripheral venous catheter) or mixed venous sample (from distal port of pulmonary artery catheter). Instead of peripheral venous blood gases, central venous blood gasses are preferred more since they correlate well with arterial blood gases and are proven by research and clinical experience. A VBG test provides venous oxygen tension, carbon dioxide tension, acidity, haemoglobin saturation, and serum bicarbonate concentration. Generally, specimen volume is 01 mL (minimum 0.5 mL), and it is stable for 30 minutes.

What are the Similarities Between ABG CBG and VBG?

  • ABG, CBG, and VBG are blood gas tests.
  • All three types of tests analyze similar parameters.
  • The main analyzed parameter that is common to all three tests is the effectiveness of the lungs for gas exchange.
  • Whole blood is the specimen type for all three tests.
  • All three tests use a specimen of 1 mL with a minimum of 0.5 mL

What is the Difference Between ABG CBG and VBG?

ABG uses arterial blood while CBG uses capillary blood, and VBG uses veinous blood. Thus, this is the key difference between ABG CBG and VBG. ABG is the most clinically significant test. But due to various difficulties in obtaining samples, CBG and VBG are two alternate tests conducted. CBG is performed for infants and adults with fragile arteries and veins. VBG is common and utilized more in intensive care units.

The below infographic presents the differences between ABG CBG and VBG in tabular form for side by side comparison.

Summary – ABG vs CBG vs VBG

Blood gas tests assess levels of oxygen and carbon dioxide, acid-base balance, and efficiency of lungs. With the type of blood drawn, there are three types of tests as ABG, CBG, and VBG. ABG is the most clinically significant blood gas test, whilst CBG and VBG are done as alternative tests. CBG is done for infants and elderly patients with fragile veins and arteries. The main analyzed parameter common to all three tests is the effectiveness of the lungs for gas exchange. Whole blood is the specimen type for all three tests. So, this is the summary of the difference between ABG CBG and VBG.