What lab tests and imaging services do
Lab tests and imaging services are tools your doctor uses to look inside your body and understand what is happening. A lab test takes a sample—blood, urine, or tissue—and analyzes it in a laboratory to measure things like cholesterol, blood sugar, infection, or organ function. Imaging services use machines to create pictures of your body: X-rays, ultrasounds, CT scans, and MRIs show your doctor bones, organs, and soft tissue without cutting you open. Together, these services help your doctor diagnose conditions, monitor existing ones, and decide what treatment you need.
Your primary care doctor usually orders these tests. Sometimes a specialist—a cardiologist, orthopedist, or gastroenterologist—will order them too. The tests themselves are performed at a hospital, imaging center, or lab facility, often on an outpatient basis, meaning you go in, have the test, and go home the same day.
Key Takeaways
- Lab tests analyze blood, urine, or tissue samples to measure body function; imaging services use machines to create pictures of your body.
- Your doctor orders tests based on your symptoms, medical history, or routine screening; you do not order them yourself.
- Preparation varies by test type—some require fasting, others require you to stop certain medications, and some need no preparation at all.
- Insurance usually covers medically necessary tests, but you may owe a copay, coinsurance, or deductible depending on your plan.
- Results typically arrive within days to a week; your doctor's office will contact you or you can check an online patient portal.
Common lab tests and what they measure
A complete blood count (CBC) measures red blood cells, white blood cells, and platelets. It detects anemia, infection, and blood disorders. A basic metabolic panel (BMP) checks kidney function, liver function, blood sugar, and electrolytes—the salts your body needs to work properly. A lipid panel measures cholesterol and triglycerides, fats in your blood that affect heart health.
A thyroid-stimulating hormone (TSH) test checks whether your thyroid is working correctly; an overactive or underactive thyroid can cause weight changes, fatigue, and mood shifts. A urinalysis examines urine for signs of infection, kidney disease, or diabetes. Blood cultures check for bacteria or fungi in your bloodstream when infection is suspected. Doctors also order tests for specific conditions: a hemoglobin A1C measures average blood sugar over three months to diagnose or monitor diabetes, and a prostate-specific antigen (PSA) test screens for prostate cancer in men.
Common imaging services and what they show
An X-ray uses radiation to create a two-dimensional picture, best for bones and detecting fractures, pneumonia, or abnormal lung patterns. It takes seconds and requires no preparation. An ultrasound uses sound waves to create images and is often used to look at the heart, abdomen, or pregnancy; it is safe and requires no radiation. A CT scan (computed tomography) takes many X-ray images from different angles and assembles them into detailed cross-sections; it is faster than an MRI and better for detecting bone fractures or internal bleeding.
An MRI (magnetic resonance imaging) uses a powerful magnet and radio waves to create detailed pictures of soft tissue—the brain, spinal cord, joints, and organs. It takes longer than a CT scan (20 to 60 minutes) and is not safe if you have certain metal implants. A mammogram is an X-ray of the breast used to screen for or diagnose breast cancer. A colonoscopy uses a thin camera on a tube to look inside the colon and is used to screen for colorectal cancer or investigate digestive symptoms.
How your doctor decides which test you need
Your doctor orders tests based on three things: your symptoms, your medical history, and screening guidelines for your age and sex. If you have chest pain, your doctor may order an EKG (electrocardiogram) and blood tests to check for heart damage. If you have fatigue and weight loss, your doctor may order a CBC and thyroid test. If you are a woman over 40, your doctor may recommend a mammogram every one to two years. If you are over 50, your doctor may recommend a colonoscopy.
Routine screening tests are offered to people without symptoms to catch disease early. These include cholesterol screening, blood pressure checks, and cancer screenings. Your doctor will tell you which screenings are recommended for you based on your age, sex, family history, and risk factors. You do not have to have every test offered—you and your doctor can discuss which ones make sense for your situation.
How to prepare for lab tests and imaging
Preparation depends on the specific test. For many blood tests, you will be asked to fast—eat and drink nothing except water—for 8 to 12 hours before the test. This is especially true for lipid panels and glucose tests, because food changes these measurements. Your doctor's office will tell you when to stop eating; usually this means no food after midnight if your test is in the morning.
For some tests, you may need to stop taking certain medications. Blood thinners like warfarin or aspirin can affect some lab results and imaging procedures. Tell your doctor about all medications and supplements you take before your test. For imaging, you may need to remove metal objects—jewelry, watches, belts with metal buckles—because metal interferes with MRI machines. If you are pregnant or think you might be, tell your doctor before any imaging, because some types use radiation.
For a colonoscopy, you will need to clean out your colon with a special liquid preparation the day before; your doctor will give you detailed instructions. For an ultrasound of the abdomen, you may be asked to drink water and hold it in your bladder so the sound waves travel better. For most X-rays and CT scans, no special preparation is needed. Always ask your doctor's office what to do before your test—they will provide written instructions.
What happens during the test and what to expect
For a blood test, you will sit in a chair and a phlebotomist (a person trained to draw blood) will clean a small area of your arm with alcohol and insert a needle into a vein. The needle stays in for only a few seconds while blood fills a tube. You may feel a pinch or slight pressure. Some people feel lightheaded; tell the phlebotomist if you do. The whole process takes less than five minutes.
For imaging, you will be taken to a room with the machine. The technician will position you and explain what will happen. For an X-ray, you stand or lie still while the machine takes a picture—it takes seconds and you feel nothing. For an ultrasound, the technician spreads gel on your skin and moves a handheld probe over the area; you feel pressure but no pain. For a CT scan, you lie on a table that slides into a tunnel-shaped machine; you hear buzzing and clicking sounds. For an MRI, you lie on a table that slides into a large magnet; the machine is loud and you may feel vibration, but it does not hurt. MRI scans take 20 to 60 minutes, so staying still is important.
Understanding your results and next steps
Lab results usually arrive within one to three days; imaging results may take a few days longer because a radiologist (a doctor who specializes in reading images) must review them. Your doctor's office will contact you with results, or you may be able to see them on a patient portal—a secure website where you can view your medical records. If results are abnormal, your doctor will call you to discuss what they mean and what happens next.
Do not panic if a result is flagged as "abnormal." Many abnormal results are minor or expected. Your doctor will explain whether the finding needs treatment, more testing, or just monitoring. If you do not hear from your doctor within a week, call the office to ask about your results—sometimes results get delayed or overlooked. Keep copies of your test results for your own records; they are useful if you see a new doctor or need to compare results over time.
Cost and insurance coverage
Insurance usually covers lab tests and imaging when your doctor orders them for a medical reason. However, you may owe money depending on your plan. A copay is a fixed amount you pay each visit—often $20 to $50 for a lab or imaging appointment. Coinsurance means you pay a percentage of the cost after you meet your deductible. A deductible is the amount you must pay out of pocket before insurance starts paying.
Costs vary widely by location, facility, and test type. A basic blood test might cost $50 to $200 out of pocket; an MRI might cost $500 to $3,000. Before your test, ask your doctor's office or the imaging center what your out-of-pocket cost will be. If cost is a concern, tell your doctor—sometimes there are lower-cost alternatives or the test can wait. Some community health centers and urgent care clinics offer lab tests at lower cost than hospitals.
Frequently Asked Questions
Do I need to fast before all blood tests?
No. Fasting is required for lipid panels, glucose tests, and some other metabolic tests, but not for a CBC or thyroid test. Your doctor's office will tell you whether to fast for your specific test. If you are unsure, call and ask before your appointment.
Is an MRI safe if I have a pacemaker or metal implant?
Most modern pacemakers and implants are MRI-safe, but some older ones are not. Tell your doctor and the imaging center about any metal implants before scheduling an MRI. They will check whether your specific device is compatible.
What if my test result is abnormal?
Your doctor will contact you to discuss what the result means. Many abnormal results are minor or expected given your symptoms. Your doctor will explain whether you need treatment, more testing, or monitoring. Ask questions if you do not understand the result or what comes next.
Can I eat or drink before an imaging test?
It depends on the test. For most X-rays, CT scans, and MRIs, you can eat and drink normally. For abdominal ultrasounds, you may be asked to fast. For colonoscopies, you will need to follow a special preparation. Your doctor's office will give you specific instructions.
How long do imaging results take?
Lab results usually arrive within one to three days. Imaging results may take a few days longer because a radiologist must review the images. Your doctor's office will contact you, or you can check your patient portal. If you have not heard anything within a week, call to follow up.