Diagnostic Tests

What a diagnostic test is

Diagnostic tests help your care team answer a focused question about your health. A test may confirm or rule out a condition, measure how severe it is, guide treatment choices, or monitor how well a treatment is working. You might have testing because you have symptoms, because a prior test suggested a concern, or to check your health during ongoing care.

Common types of tests

Laboratory tests

These include blood, urine, and other body samples. They can look for infection, measure organ function, check hormone levels, monitor medicines, or detect markers of inflammation. Results often come with a reference range. Values outside the range do not always mean disease. Your clinician will interpret them in the context of your history and exam.

Imaging tests

Imaging creates pictures of the inside of your body. Common examples include X ray, ultrasound, computed tomography, magnetic resonance imaging, and nuclear medicine scans. Each method has strengths and limits. For example, ultrasound uses sound waves and does not use ionizing radiation, while computed tomography and X ray do use ionizing radiation.

Procedures and biopsies

Some tests involve collecting a small tissue sample or viewing the inside of the body with a scope. Examples include biopsy, endoscopy, and colonoscopy. These procedures can help confirm a diagnosis and sometimes allow treatment at the same time.

Why your clinician orders a test

Your clinician orders testing to answer a specific clinical question. Reasons include confirming a suspected diagnosis, ruling out a dangerous condition, defining disease stage, guiding the safest treatment, checking for side effects, or following your progress over time. If the purpose is not clear to you, ask what question the test should answer and how the result may change your care.

How to prepare

Good preparation helps you get accurate results and avoid repeat testing.

• Ask if you should fast or avoid certain foods or drinks
• Review all prescriptions, over the counter medicines, and supplements that could affect results
• Share allergies and prior reactions to contrast materials or medicines
• Plan transportation and recovery time if sedation may be used
• Wear comfortable clothing and leave jewelry at home for imaging
• Bring your identification and insurance card if applicable

Making sense of sensitivity, specificity, and other metrics

Test accuracy is about how well a test distinguishes between people who have a condition and those who do not.

• Sensitivity measures how often a test correctly identifies people who have the condition
• Specificity measures how often a test correctly identifies people who do not have the condition
• Positive predictive value is the chance you truly have the condition when the test is positive
• Negative predictive value is the chance you truly do not have the condition when the test is negative
• Likelihood ratios combine sensitivity and specificity to show how much a result changes the chance of a condition being present

No single number tells the whole story. Your clinician considers your symptoms and risk factors before and after a test to estimate what the result really means for you.

Risks, limits, and false results

Every test has potential downsides. These can include discomfort, bleeding, infection, exposure to ionizing radiation, or reactions to contrast material. False positive results can trigger worry and follow up procedures. False negative results can delay a diagnosis. Incidental findings may lead to additional testing even when they are unlikely to matter. Discuss the benefits and the risks before you proceed.

Screening tests versus diagnostic tests

Screening looks for a condition before symptoms appear. Examples include cervical cancer screening with Pap test and human papillomavirus test, and breast cancer screening with mammography. Diagnostic testing investigates a known sign or symptom, or follows up on an abnormal screening result. A screening test that is positive usually needs a diagnostic test to confirm the finding.

Quality and safety of testing

Quality standards help ensure that tests performed on human specimens are reliable and accurate. In the United States, most clinical laboratories must meet national quality requirements for personnel, processes, and proficiency testing. Imaging services also follow practice standards to support safety and quality.

Questions to ask before a test

• What question is this test meant to answer
• How will the result change my care
• What are the benefits and risks
• Are there alternatives that could answer the same question
• Do I need to prepare in a specific way
• When and how will I get results
• Will I need repeat testing
• What costs should I expect and is this in network for my insurance

What happens after the test

Your care team reviews the results with your history, symptoms, and prior studies. Some results call for watchful waiting and repeat testing later. Others may lead to treatment, referral, or additional targeted tests. Ask for a copy of your report and keep it with your records.

When to seek support

If coordinating testing feels overwhelming, you can ask for help with scheduling, reminders, transportation planning, and communication between your clinicians. Support can make it easier to prepare well, complete testing on time, and follow through on next steps.

Key takeaways

• Diagnostic tests answer specific questions and guide care
• Preparation and clear communication improve accuracy and safety
• Results always make the most sense when viewed alongside your symptoms and risk factors
• Shared decision making helps you weigh benefits and risks and choose what fits your goals

FAQ

• What is a diagnostic test?
  A diagnostic test is a medical test ordered to answer a specific question about your health. It can confirm or rule out a condition, show how severe it is, guide treatment choices, or monitor how well a treatment is working.
• What are the main types of diagnostic tests?
  Common types include laboratory tests (blood, urine, and other samples), imaging tests (X ray, ultrasound, CT, MRI, nuclear scans), and procedures or biopsies that collect tissue or use a scope to look inside the body.
• Why did my clinician order this test?
  Your clinician orders a test to answer a focused question, such as confirming a suspected diagnosis, ruling out something dangerous, staging a disease, checking for side effects, or tracking your progress. You can ask what question the test is meant to answer and how the result may change your care.
• How should I prepare for a diagnostic test?
  Preparation may include fasting, avoiding certain foods or medicines, sharing your allergies and prior reactions, arranging transportation if sedation is used, wearing comfortable clothing without metal, and bringing your ID and insurance card.
• What do sensitivity and specificity mean for my test?
  Sensitivity is how often a test correctly finds people who have a condition. Specificity is how often it correctly shows a condition is not present. These and related measures help your clinician interpret how much to trust a positive or negative result in your situation.
• Can test results be wrong?
  Yes. A false positive suggests a problem that is not really there and may lead to extra tests. A false negative misses a condition and can delay diagnosis. Incidental findings can also appear that may not be important but still prompt follow up.
• How is a screening test different from a diagnostic test?
  Screening tests look for disease before symptoms appear, such as mammograms or Pap tests. Diagnostic tests are used when there is a symptom, sign, or abnormal screening result and are aimed at clarifying what is actually going on.
• Are there quality and safety standards for testing?
  Most clinical laboratories and imaging centers follow national standards for staff training, equipment, procedures, and regular quality checks to help keep results reliable and testing as safe as possible.
• What should I ask before having a test?
  You can ask what question the test answers, how it might change your care, what benefits and risks there are, whether there are alternatives, how to prepare, when and how you will get results, and what the likely costs are.
• What happens after the test is done?
  Your care team interprets the result alongside your symptoms, history, and other tests. They may recommend watchful waiting, repeat testing, treatment, referral, or more focused tests. Ask for a copy of your report and guidance on next steps.
• What if managing all these tests feels overwhelming?
  If scheduling, transportation, or follow up is hard, you can ask for help with coordination and reminders. Support from an advocate, care coordinator, or trusted caregiver can make it easier to prepare, complete testing on time, and understand what comes next.

References

• MedlinePlus. Diagnostic Tests. https://medlineplus.gov/diagnostictests.html
• MedlinePlus. Medical Tests. https://medlineplus.gov/lab-tests/
• MedlinePlus. How to Understand Your Lab Results. https://medlineplus.gov/lab-tests/how-to-understand-your-lab-results/
• MedlinePlus. Diagnostic Imaging. https://medlineplus.gov/diagnosticimaging.html
• Mayo Clinic. Tests and Procedures. https://www.mayoclinic.org/tests-procedures
• Cleveland Clinic. Diagnostics and Testing. https://my.clevelandclinic.org/health/diagnostics
• NCBI Bookshelf. Diagnostic Testing Accuracy: Sensitivity, Specificity, and Predictive Values. https://www.ncbi.nlm.nih.gov/books/NBK557491/
• NCBI Bookshelf. Appendix: Test Performance Metrics. https://www.ncbi.nlm.nih.gov/books/NBK98249/
• Centers for Disease Control and Prevention. Overview of Testing for SARS CoV 2. https://www.cdc.gov/covid/hcp/clinical-care/overview-testing-sars-cov-2.html
• Centers for Disease Control and Prevention. Cancer Screening Tests. https://www.cdc.gov/cancer/prevention/screening.html
• Centers for Disease Control and Prevention. Clinical Laboratory Improvement Amendments About CLIA. https://www.cdc.gov/clia/php/about/index.html
• Agency for Healthcare Research and Quality. The SHARE Approach to Shared Decision Making. https://www.ahrq.gov/sdm/share-approach/index.html

This content is for education only and does not replace professional medical advice. If you have new weakness, severe pain, fever with confusion, chest pain, or trouble breathing, call emergency services.