Blood tests are an essential diagnostic tool used by doctors to check for a wide range of health conditions. They provide valuable information about what’s going on inside your body and can help uncover issues that you may not be aware of. But while blood tests are extremely useful, they do have some limitations. There are many things that routine blood tests cannot tell you.
What are blood tests?
Blood tests, also known as blood work or blood panels, are medical tests that analyze a sample of your blood. They check for levels of various components like cells, proteins, nutrients, and waste products. Doctors order blood tests to:
- Screen for health disorders
- Confirm diagnoses
- Assess organ function
- Monitor ongoing conditions
- Detect vitamin deficiencies
- Identify infections or illnesses
- Check drug levels
- Evaluate overall health
Some common blood tests include:
Test | Checks for |
---|---|
Complete blood count (CBC) | Levels of different cells like red blood cells, white blood cells, and platelets |
Basic metabolic panel (BMP) | Electrolyte and fluid balance, kidney function, blood sugar |
Lipid panel | Cholesterol and triglyceride levels |
Liver function tests (LFTs) | Liver enzymes that may indicate liver damage or disease |
Thyroid panel | Hormone levels to evaluate thyroid function |
Blood tests require collecting a blood sample, usually obtained by needle from a vein in your arm. After the blood is drawn, it is sent to a lab for analysis.
What can blood tests detect?
Blood tests can reveal many things about your health, such as:
- Anemia or blood disorders
- Infection or inflammation
- Kidney or liver problems
- Diabetes
- Cancer
- Coronary heart disease risk
- Hormonal imbalances
- Nutrient deficiencies
- Exposure to toxic substances
- Certain genetic diseases
They also provide vital information to monitor ongoing conditions like diabetes, kidney disease, and autoimmune disorders.
What are the limitations of blood tests?
While blood tests can detect a wide array of diseases and health problems, they do have some limitations:
- They only assess what’s circulating in the blood at the moment the sample was taken. Levels can fluctuate.
- Abnormal results don’t always mean there’s a problem. Other factors can cause temporary changes.
- Normal results don’t guarantee you’re 100% healthy. Some conditions don’t show up right away.
- Most blood tests can’t detect the actual cause of an abnormality found.
- Blood tests check individual components and may miss interactions between systems.
- Many blood tests lack standard reference ranges tailored to age, sex, and ethnicity.
- False positive and false negative results are possible.
What routine blood tests can’t tell you
There are several important health factors that routine blood work does not provide information about. Here are some examples:
Cancer
General blood tests cannot screen for or diagnose cancer. They can sometimes detect blood cell changes or elevated tumor markers that may prompt further cancer testing. But you need specific imaging tests and tissue biopsies to determine if cancer is present.
Pain
Blood tests reveal no information about physical symptoms like pain. You could have completely normal blood work but still be experiencing migraines, arthritis, nerve pain, back pain, or other issues causing discomfort. Imaging, physical exams, and pain questionnaires are required to assess pain.
Mental health conditions
Blood tests do not indicate psychological disorders like depression, anxiety, bipolar disorder, schizophrenia, PTSD, or personality disorders. Evaluating mental health involves psychiatric evaluation, patient histories, and assessment of thoughts, moods, and behaviors.
Neurological disorders
Conditions like multiple sclerosis, Parkinson’s, Alzheimer’s, epilepsy, and stroke will not show up in routine blood work. These require imaging like MRIs, EEGs, neurological exams, cognitive testing, and evaluation of symptoms.
Autoimmune diseases
Many autoimmune disorders like rheumatoid arthritis, lupus, and inflammatory bowel disease can’t be detected through general blood tests. Doctors must order specific autoantibody tests along with biopsies and scans to diagnose autoimmunity.
Injuries and structural problems
Blood tests reveal nothing about physical injuries, joint/bone damage, or anatomical defects. Assessing these issues requires medical imaging, surgical evaluation, endoscopies, tissue biopsies, and physical examination of the affected areas.
Sleep disorders
Conditions like sleep apnea, insomnia, and restless leg syndrome are not identifiable from blood work. Sleep studies, home sleep tests, EMG studies, and sleep logs are needed to diagnose sleep disorders.
Allergies and intolerances
General blood tests do not detect allergies or intolerances to foods, medications, environmental allergens, chemicals, etc. These require specialized IgE antibody blood tests, skin prick tests, elimination diets, and oral food or patch allergen challenge testing.
Developmental delays
Blood tests cannot identify developmental delays and disorders like autism, ADHD, speech delays, coordination problems, and intellectual disabilities. These require developmental screening tools, neuropsychological testing, clinical observation, and diagnostic assessment by psychologists.
Genetic disorders
Many genetic conditions are not picked up on routine blood work. Specific DNA tests are needed to identify genetic mutations linked to disorders like cystic fibrosis, sickle cell disease, Tay Sachs, hemophilia, and thousands of other inherited conditions.
When are blood tests helpful?
Despite their limitations, blood tests are still extremely useful and widely-used diagnostic tools. Here’s when blood work is most helpful:
- As an initial broad screening for general health issues
- If you’re experiencing symptoms and your doctor doesn’t know the cause
- To confirm suspected diagnoses based on your symptoms
- To monitor chronic conditions and adjust treatment if needed
- To check for side effects or complications from medications
- To identify vitamin/mineral deficiencies based on symptoms
- To establish baseline biomarkers for future comparison
- To perform routine screening for common conditions like diabetes
- To provide supporting data along with other tests for a more complete evaluation
Blood tests are most useful when doctors use them selectively based on clinical judgement, along with a full patient history, physical examination, and any medical imaging or other testing needed.
Takeaways
Here are the key takeaways about what blood tests can and cannot tell you:
- Blood tests check for many health issues but cannot detect all diseases or conditions.
- They cannot directly diagnose the cause of vague symptoms or pinpoint the origin of abnormalities found.
- Normal blood results do not guarantee you are completely healthy or rule out serious illnesses.
- Blood tests only assess circulating components at the moment in time the sample was collected.
- Conditions like cancer, pain disorders, neurologic diseases, mental illness, injuries, and genetic abnormalities require other specialized tests.
- Blood work is most helpful when used selectively and combined with a full clinical evaluation.
- Talk to your doctor about any concerning symptoms even if your blood tests are normal.
- Ask your doctor to explain what specific conditions can and cannot be assessed from your blood tests.
Conclusion
Blood tests are a critically important diagnostic tool that can assess many aspects of your health. But they have limitations and cannot provide a complete picture on their own. Blood tests only analyze the blood components, not tissues, organs, or structures. Many diseases will not show up on routine blood work at all. That’s why it’s essential for doctors to use their clinical judgement to order the right blood tests at the right time and interpret results along with your full medical history and any other necessary testing. While blood work offers valuable data, it does not tell you everything. But used properly, it can provide key pieces to the puzzle in making an accurate diagnosis and optimizing your health.