Carbon monoxide (CO) poisoning is a serious health concern. CO is an odorless, colorless gas that is produced when fuels like gasoline, oil, propane, and wood don’t burn completely. When you breathe in CO, it replaces oxygen in your red blood cells, reducing the amount of oxygen that reaches your body’s tissues and organs. This can lead to serious tissue damage, or even death.
CO poisoning can be easy to miss because its symptoms are similar to other conditions like the flu or food poisoning. This makes blood tests an important tool for diagnosis. So does carbon monoxide poisoning actually show up in blood tests? The short answer is yes.
How Carbon Monoxide Affects the Body
To understand how CO poisoning shows up on blood tests, it helps to understand how CO affects the body. When you inhale CO, it diffuses into your bloodstream through your lungs. In your blood, CO binds tightly to hemoglobin, the protein in red blood cells that carries oxygen.
Hemoglobin’s normal job is to pick up oxygen from the lungs and deliver it to tissues and organs. But CO binds to hemoglobin much more readily than oxygen does. When CO is around, hemoglobin prefers to bind with CO instead of oxygen.
This leaves less hemoglobin available to carry oxygen. It also causes oxygen levels in your blood to drop. With less oxygen circulating, tissues and organs can be starved of oxygen. This lack of oxygen leads to the symptoms and health effects of CO poisoning.
Effects on Different Organs and Tissues
Lack of oxygen affects some organs and tissues more than others. Here’s a look at some of the key effects of CO poisoning on the body:
- Brain: The brain is very sensitive to oxygen deprivation. CO poisoning can lead to headaches, dizziness, confusion, seizures, unconsciousness, and permanent brain damage.
- Heart: Lack of oxygen damages heart muscle and can cause chest pain, shortness of breath, irregular heartbeat, and heart attack.
- Blood vessels: CO poisoning restricts blood flow and makes blood more likely to clot inside vessels.
- Lungs: People may develop respiratory failure due to lack of oxygen.
- Muscles: CO poisoning can cause muscle weakness, pain, and breakdown.
- Skin: Some people develop cherry-red skin color.
- Pregnancy: CO poisoning increases the risk of miscarriage and birth defects.
As you can see, the effects of CO poisoning can be serious and wide-ranging. Next, we’ll look specifically at how this shows up in blood tests.
Carbon Monoxide and Blood Tests
There are a few different blood tests that can detect CO poisoning:
1. Carboxyhemoglobin (COHb) Test
This test directly measures the level of CO bound to hemoglobin in the blood. It’s reported as a percentage.
In normal conditions, less than 3% of hemoglobin is bound with CO. In CO poisoning, the COHb level rises. Mild poisoning shows COHb levels of 10-20%. Severe poisoning causes levels higher than 20%, up to 50-60%.
So an elevated COHb strongly suggests CO poisoning. However, normal COHb levels don’t rule out mild or early CO toxicity. That’s because CO can cause symptoms even before COHb rises significantly.
2. Arterial Blood Gas
This blood test evaluates oxygen and carbon dioxide levels. It requires blood drawn directly from an artery.
In CO poisoning, this test would show low blood oxygen levels (hypoxemia). The degree of oxygen deprivation correlates with the severity of the poisoning.
However, other medical conditions can also cause low oxygen levels. So this result alone doesn’t confirm CO toxicity.
3. Complete Blood Count
This common test checks levels of different cells in blood. CO poisoning can lead to high red blood cell counts (polycythemia). It’s the body’s way of compensating for reduced oxygen-carrying capacity.
Again, other disorders also raise red blood cell count. So this finding supports CO poisoning but isn’t definitive.
4. Comprehensive Metabolic Panel
This blood screen includes tests like electrolytes, kidney and liver function, and glucose. In CO poisoning, it may show:
- High lactate level
- Metabolic acidosis (excess acidity)
- Elevated muscle enzymes like CPK from muscle damage
These abnormalities provide additional evidence of CO toxicity. But they can also occur with other conditions.
Other Testing Considerations
A few other points about blood testing for CO poisoning:
- Results can vary based on when blood is drawn relative to CO exposure.
- Blood tests may be normal if the person is tested long after exposure ended.
- COHb levels only reflect recent exposures from the past several hours.
- A normal COHb doesn’t rule out CO poisoning.
- The diagnosis is usually based on a combination of test results and a person’s symptoms.
Because of these factors, no single blood test can definitively diagnose CO toxicity by itself. Doctors must interpret blood test results in the broader context of a patient’s presentation. But abnormal results can provide objective evidence that supports the diagnosis.
Treatment
The main treatment for CO poisoning involves removing the person from the source of exposure and giving them oxygen to breathe. This helps displace CO from hemoglobin and restore normal oxygen levels.
Depending on the severity, other treatments might include:
- High-flow oxygen masks or hyperbaric oxygen therapy
- Fluids and electrolytes
- Respiratory support like ventilation
- Medications to improve blood flow
- Antidotes like hydroxocobalamin to bind with CO
With prompt treatment, many people recover fully from CO poisoning. But delays in diagnosis and therapy increase the risk of permanent damage and death.
Prevention
The best way to avoid CO poisoning is prevention:
- Install CO detectors at home, especially near sources of combustion like furnaces, water heaters, and fireplaces.
- Have furnaces, chimneys, fireplaces, and vents properly maintained.
- Never run vehicles or gas-powered tools like generators indoors, even if doors are open.
- Don’t use gas stoves for heating.
- Don’t sit in running vehicles with the garage door closed.
Being aware of the symptoms of CO poisoning can also help people recognize it quickly. Call emergency services or go outside to fresh air if you suspect CO exposure. Prompt action is vital to limit damage from this “silent killer.”
Conclusion
In summary, blood testing plays an important role in diagnosing CO toxicity. Elevated COHb levels strongly indicate CO exposure. Low oxygen and high red blood cell counts provide supporting evidence. However, normal test results don’t rule out mild or recent CO poisoning. Doctors diagnose CO toxicity based on a combination of blood test abnormalities and the person’s symptoms and history. The key is to test quickly and start oxygen therapy without delay. With prompt treatment guided by blood tests, patients with CO poisoning often recover without permanent effects.