From the Guidelines
Very dark blood during a phlebotomy typically indicates deoxygenated blood, which is normal and not usually a cause for concern. Blood appears darker when it contains less oxygen, such as in venous blood drawn during routine blood tests. This is a normal physiological finding since venous blood has already delivered much of its oxygen to tissues before returning to the heart.
Key Points to Consider
- In some cases, extremely dark blood might suggest poor oxygenation due to respiratory problems, circulation issues, or dehydration.
- Certain medical conditions like polycythemia vera (where the body produces too many red blood cells) can also cause blood to appear darker than usual, as noted in guidelines for managing adults with congenital heart disease 1.
- According to the acc/aha 2008 guidelines, therapeutic phlebotomy is indicated for hemoglobin greater than 20 g per dL and hematocrit greater than 65%, associated with headache, increasing fatigue, or other symptoms of hyperviscosity in the absence of dehydration or anemia 1. If you're concerned about the appearance of your blood during phlebotomy, mention it to your healthcare provider, especially if you're experiencing symptoms like shortness of breath, fatigue, or dizziness. However, in most cases, dark blood during a routine blood draw is completely normal and simply reflects the natural oxygen content of venous blood.
Considerations for Healthcare Providers
- When evaluating dark blood during phlebotomy, consider the patient's overall clinical context, including symptoms and medical history.
- The presence of dark blood alone is not typically a cause for immediate concern but should be considered in the context of other clinical findings.
From the Research
Blood Color and Phlebotomy
- Having very dark blood when getting a phlebotomy can be an indication of various medical conditions, but the provided studies do not directly address the cause of dark blood color in the context of phlebotomy 2, 3, 4.
- However, a study on hemodialysis patients found that darkened blood color is often observed in critically ill patients due to decreased oxygen saturation, and it can also be influenced by inflammation 5.
- The study also found that blood color was positively correlated with mean corpuscular hemoglobin concentration and serum sodium concentration, as well as blood oxygen saturation 5.
- Another study reviewed the usefulness of complete blood count (CBC) in assessing cardiovascular and metabolic diseases, but it did not specifically address the issue of dark blood color during phlebotomy 6.
Possible Causes of Dark Blood Color
- Decreased oxygen saturation 5
- Inflammation 5
- Other medical problems, such as anemia or hematologic disorders 3, 4