Carbon Dioxide (P-) – Analysis of Acid-Base Balance
P-Carbon dioxide, also called total carbonic acid, is a blood test that primarily reflects the amount of bicarbonate in plasma. Bicarbonate is an important part of the body's buffer system and helps to keep the pH of the blood within a normal range.
The analysis is used as an indicative measure of the metabolic part of the body's acid-base balance. A deviating value can provide guidance on, for example, metabolic acidosis or metabolic alkalosis and can be particularly relevant in conditions that affect kidney function, fluid and electrolyte balance or metabolism.
Why analyze Carbon Dioxide (P-)?
A Carbon Dioxide (P-) analysis can be used for several purposes:
- Assess acid-base balance – The test can provide an initial indication of whether the metabolic part of the acid-base balance is disturbed.
- Investigate low bicarbonate – A low value can be seen in metabolic acidosis, for example in renal failure, diabetic ketoacidosis or certain gastrointestinal losses.
- Investigate high bicarbonate – A high value can occur in metabolic alkalosis, for example in prolonged vomiting or certain fluid and electrolyte disorders.
- Assess the influence of the kidneys on acid-base balance – The kidneys have an important role in the regulation of bicarbonate and the excretion of acids, which makes the analysis relevant in cases of impaired renal function.
- Complement other blood tests – Carbon dioxide (P-) is often assessed together with, for example, sodium, potassium, chloride, creatinine, glucose and, if necessary, blood gas.
Reference values for Carbon Dioxide (P-)
The reference range varies depending on age:
- Adults ≥18 years: 22–28 mmol/L
Reference intervals may vary between different laboratories. The result should therefore be assessed against the reference interval stated on the current test result.
What can an abnormal Carbon Dioxide (P-) mean?
A low Carbon Dioxide (P-) usually means that the bicarbonate level is lowered and can occur in metabolic acidosis, among other things. A high value usually means an elevated bicarbonate level and can occur in metabolic alkalosis, among other things.
Respiratory conditions can also affect the result because the lungs and kidneys together regulate the body's acid-base balance. Carbon Dioxide (P-) is therefore an indicative analysis and cannot be used alone to establish a specific diagnosis.
How is the blood sample taken?
Carbon Dioxide (P-) is analyzed through a standard venous blood sample. The sample requires proper handling as contact with air can affect the carbon dioxide content and give a falsely low result.
Analysis of Carbon Dioxide (P-) may be relevant for those who want to get a better picture of the body's acid-base balance or follow up on conditions that may affect the kidneys' or metabolism's regulation of bicarbonate. In case of deviating results, additional samples, such as electrolytes, kidney function tests or blood gas, may be needed for a more complete assessment.
