Doctor-Reviewed Health Guides: Conditions, Procedures & Health News

A fecal calprotectin test is a stool test that measures calprotectin, a protein released by white blood cells. High levels mean there's inflammation in the intestines, which points toward inflammatory bowel disease (IBD). Normal levels make inflammation unlikely and support irritable bowel syndrome (IBS), which can help some people avoid a colonoscopy. You collect the sample at home.

A CD4 count is a blood test that measures CD4 cells, a type of white blood cell that coordinates the immune response. HIV destroys these cells, so the count shows how strong the immune system is. A normal CD4 count is about 500–1,200 cells/mm³. A count of 200 or below defines stage 3 HIV (AIDS).

The C4 complement blood test measures complement component 4 (C4), a protein that helps the immune system fight bacteria and viruses. It's ordered to help diagnose and monitor lupus and other autoimmune diseases and to look for hereditary angioedema. A typical normal range is 14–45 mg/dL. It's a simple blood draw, often done together with C3.

The APOE gene test is a genetic test that shows which versions of the apolipoprotein E (APOE) gene you carry. Carrying APOE4 increases the risk of late-onset Alzheimer's disease, while APOE2 is linked to lower risk. It shows risk, not a diagnosis: many people with APOE4 never develop Alzheimer's. Genetic counseling before and after testing is recommended.

A sentinel node biopsy (SLNB) is a surgical test that checks whether cancer has spread from a tumor to the nearby lymph nodes. The sentinel nodes are the first lymph nodes that fluid from the tumor drains into. It's used for breast cancer and melanoma. If the sentinel nodes are clear, cancer is unlikely to have spread further.

An allergy skin test helps find out what you're allergic to by placing tiny amounts of possible allergens on or under the skin and watching for a reaction. The three types are the skin prick test, the intradermal test and the patch test. You'll usually need to stop antihistamines beforehand.

Tumor markers are substances, usually proteins, that cancer cells, or the body in response to cancer, make in larger amounts. Most are measured in a blood test. Common examples include PSA (prostate cancer), CA 125 (ovarian cancer) and CEA (colon cancer). A high level alone never proves cancer, and a normal level can't rule it out.

A visual evoked potential (VEP) test measures the electrical signal the brain's visual cortex produces when you look at a pattern, usually a flashing checkerboard on a screen. It's most often ordered to look for optic nerve damage from multiple sclerosis and optic neuritis. It's painless and takes up to 60 minutes.

A digital rectal exam (DRE) is a quick physical exam in which a provider gently inserts a gloved, lubricated finger into the rectum to feel for problems in the lower rectum, anus and prostate gland. It can help find hemorrhoids, anal fissures, lumps and prostate enlargement. It takes a few minutes and may feel uncomfortable but shouldn't hurt.

The Apley test is a quick physical exam that checks for a torn meniscus, the C-shaped cartilage cushion in the knee. You lie face down with the knee bent while the provider twists and presses on your foot. Pain, catching or popping suggests a meniscus tear. It's not perfectly accurate, so MRI is often the next step.

A hip X-ray uses a small dose of radiation to create pictures of the hip joint and nearby pelvic bones. It's often the first test for hip pain, a limp, swelling or an injury, and it can show fractures and arthritis. It takes about 10 minutes. Soft-tissue problems such as a labral tear need MRI or CT instead.

The CEA test is a blood test that measures carcinoembryonic antigen, a protein that some cancers release into the blood. It's a tumor marker used mainly to monitor colorectal cancer: to see whether treatment is working and to watch for recurrence. It's not used to screen for or diagnose cancer. Normal levels are about 0–3 ng/mL in nonsmokers.

A Meckel's scan is a nuclear medicine test that looks for a Meckel's diverticulum, a small pouch in the small intestine present from birth that can cause painless rectal bleeding, especially in children. A radioactive tracer injected into a vein collects in stomach-type tissue. The test is about 90% accurate in children but about 50% in adults.

The C3 complement blood test measures complement component 3 (C3), a protein in the complement system, part of the immune defense against infection. Providers order it to help diagnose and monitor lupus, certain kidney diseases, vasculitis and recurrent infections. The normal range is about 80–178 mg/dL. It's a simple blood draw, often done with C4.

A karyotype test looks at the chromosomes, the structures inside cells that carry your genes, to check their number, size and shape. It can find extra, missing or rearranged chromosomes that cause conditions such as Down syndrome and Turner syndrome, and changes linked to some blood cancers. Results usually take a few weeks.

A vascular ultrasound (duplex study) is a painless, noninvasive test that uses sound waves to create images of the arteries and veins and measure how blood flows through them. It helps find blood clots, narrowed or blocked arteries, carotid artery disease, aneurysms and varicose veins. There's no radiation and no side effects.

A cardiopulmonary exercise test (CPET), also called a metabolic exercise stress test, checks how well the heart, lungs and muscles work together during exercise. You walk on a treadmill or pedal a bike while breathing through a mask that measures the oxygen you use. Unlike a standard stress test, it shows why you get short of breath or tired.

A SPECT scan (single-photon emission computed tomography) is a nuclear medicine test that creates 3D images showing how organs work, not just how they look. A small amount of radiotracer is injected into a vein, and a gamma camera rotates around you. It's most often used for the heart, brain and bones. A scan takes about 30 minutes.

An oral drug test (mouth swab or saliva drug test) checks a sample of saliva for alcohol, drugs or medicines. It detects recent use, usually within a few hours to about two days, depending on the drug. You can't eat or drink for at least 10 minutes beforehand. A positive screen is usually confirmed by a lab.

Lymphoscintigraphy (lymph node mapping) is a nuclear medicine imaging test that shows how lymph fluid flows through the lymphatic system. A radioactive tracer is injected under the skin, and a gamma camera follows it to nearby lymph nodes. It's often used before surgery for breast cancer and melanoma to find the sentinel lymph node and to diagnose lymphedema.

Gadolinium contrast is a dye given through an IV during an MRI to make blood vessels, inflammation, abnormal tissues and tumors show up more clearly. Healthy kidneys remove it within 24 hours. Most people have no or mild side effects, and serious allergic reactions are rare. If you have severe kidney disease, tell your care team beforehand.

A depth perception test (stereopsis test) checks whether the two eyes work together and whether the brain combines their images to judge depth and distance in 3D. It's quick, painless and doesn't need dilating drops. It's especially important for children at risk of lazy eye or crossed eyes, which can permanently reduce depth perception if not treated early.

Deep tendon reflexes (DTRs) are automatic muscle responses that a provider tests by tapping a tendon with a rubber reflex hammer. Each is graded from 0 (absent) to 4+ (very brisk), with 2+ typical. Reflexes that are too weak, too strong or different on each side can point to problems in the nerves, spinal cord or brain.

A sputum culture is a lab test that looks for bacteria or fungi in sputum, the mucus coughed up from deep in the lungs. It helps diagnose lung infections such as pneumonia and tuberculosis, identifies the exact germ and shows which medicines will work against it. You cough into a sterile cup. Results usually take a few days.