An arterial blood gas (ABG) test provides a snapshot of a patient’s respiratory and metabolic well-being. This diagnostic tool measures the levels of oxygen and carbon dioxide in arterial blood, along with its acid-base balance, expressed as pH. Clinicians rely on ABG results to quickly assess lung function and how effectively the body manages its metabolic processes. The accuracy of these results is influenced by how the blood sample is handled after collection. Leaving an ABG specimen at room temperature for too long can significantly alter its measured values, leading to incorrect clinical assessments.
Why Temperature Affects ABG Samples
Blood contains active cells, such as white blood cells and platelets, that continue metabolic activities after collection. These cells consume oxygen and glucose, producing carbon dioxide and lactic acid.
This ongoing metabolic process directly influences the concentrations of gases and acids in the sample. The rate of these biochemical reactions is highly sensitive to temperature. At room temperature, cellular metabolism proceeds at a faster pace compared to cooler conditions, leading to more rapid changes in the blood gas parameters.
How ABG Values Change Over Time
When an ABG specimen remains at room temperature, specific changes occur. The partial pressure of oxygen (PaO2) typically decreases as cells consume oxygen. Conversely, the partial pressure of carbon dioxide (PaCO2) increases because cellular metabolism produces carbon dioxide as a waste product.
The pH of the blood sample also declines, becoming more acidic. This drop in pH is a direct consequence of increased carbon dioxide levels, which form carbonic acid, and the accumulation of lactic acid. Glucose levels diminish as cells utilize it, and lactate levels rise. Bicarbonate levels may also shift, reflecting changes in pH and carbon dioxide, as the sample’s buffering systems are no longer active.
Impact of Incorrect ABG Results
Receiving inaccurate ABG results due to improper sample handling can have serious consequences for patient care. Misleading values might lead to a misdiagnosis, such as falsely indicating respiratory acidosis or hypoxia. This can cause clinicians to administer inappropriate treatments. For example, a falsely low PaO2 might prompt unnecessary oxygen administration, or incorrect ventilator settings could be applied based on skewed PaCO2 readings.
Such errors can delay appropriate and effective treatment. When clinicians act on flawed data, they may miss the underlying issue, prolonging illness or worsening the patient’s condition. Patient safety is compromised when medical decisions are based on unreliable laboratory results.
Correct Handling of ABG Samples
Proper handling of ABG specimens is important for ensuring accurate results. The most effective measure is prompt analysis of the sample, ideally within 10 to 15 minutes of collection. If immediate analysis is not possible, particularly when delays extend beyond 15-30 minutes, the sample should be placed in an ice slurry. Chilling the sample significantly slows the metabolic activity of blood cells, minimizing changes to gas and pH values.
Before analysis, the sample must be thoroughly mixed to ensure homogeneity and prevent clotting. Any air bubbles introduced during collection should be expelled immediately, as they can alter the gas concentrations. While chilling helps preserve sample integrity, a chilled sample typically remains stable for up to an hour, though some parameters may show changes beyond this timeframe.