Having cold symptoms when you have a scheduled blood test is a common dilemma. This article clarifies how a common cold can impact blood test results and offers guidance on when to proceed or postpone testing.
How a Cold Can Influence Blood Test Results
A common cold triggers temporary inflammatory responses as the immune system fights the virus, affecting certain blood markers. While overall white blood cell (WBC) count may not change dramatically, the differential count can shift, and lymphocyte counts may increase.
Inflammatory markers such as C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can show temporary elevations during a cold. CRP, produced by the liver, often rises in viral infections. Similarly, ESR, which measures how quickly red blood cells settle, can also increase due to inflammation.
These temporary changes in blood markers could complicate interpretation, especially for routine screening or monitoring a chronic condition. An elevated CRP or ESR might be misinterpreted as a more serious underlying inflammatory condition, rather than a transient response to a cold. Knowing a cold can influence these values is important for proper diagnostic consideration.
When a Blood Test is Advisable During a Cold
While a common cold generally does not necessitate a blood test, testing becomes important with severe, persistent, worsening, or atypical symptoms. Seeking medical attention and a blood test is advisable. Red flag symptoms include a high fever, severe body aches, difficulty breathing, or chest pain.
These symptoms could indicate a more serious condition mimicking a cold, such as a bacterial infection like pneumonia or strep throat, or other viral illnesses like influenza or COVID-19. A complete blood count (CBC) can help differentiate between viral and bacterial infections; for instance, a high neutrophil count might suggest a bacterial cause. Specific viral tests, such as PCR for influenza or COVID-19, directly identify the pathogen causing the illness. Inflammatory markers can also help assess the severity of the infection and guide treatment decisions.
Important Considerations Before Your Blood Test
If you have a cold and a blood test is scheduled or being considered, communicating your symptoms to your healthcare provider or the lab technician beforehand is important. For routine or non-urgent tests, rescheduling might be the best course of action to ensure the most accurate results and avoid potential misinterpretation. This allows your body to return to its baseline state, providing a clearer picture of your health.
For urgent blood tests, openly communicating your cold symptoms is still important. This information allows the medical professional to interpret any altered results within the context of your current illness, helping them differentiate between changes caused by the cold and those related to the condition being investigated. Additionally, staying well-hydrated before a blood test is generally recommended, as it can make the blood collection process easier.