Understanding Diagnostic Tests: What You Need to Know

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: Diagnostic tests and what they mean for your care

• What is a diagnostic test?
  A diagnostic test helps your care team answer a focused 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.
• ‍Why might my clinician order a test?
  Common reasons include checking the cause of symptoms, ruling out dangerous problems, deciding which treatment is safest, looking for side effects, or following your progress over time. If you are not sure why a test is being done, ask what question it is meant to answer and how the result might change your care.
• ‍What are the main types of diagnostic tests?
  There are three broad groups:
  • Laboratory tests, such as blood and urine tests
  • Imaging tests, such as X ray, ultrasound, CT, MRI, or nuclear scans
  • Procedures and biopsies, such as endoscopy, colonoscopy, or tissue sampling
  Each type looks at health in a different way and has its own strengths and limits.
• ‍What should I know about lab test results and reference ranges?
  Lab results usually include a reference range. Values outside the range do not always mean disease. Some healthy people have results slightly outside the range, and some people with illness can have results in range. Your clinician interprets results together with your history and exam, not in isolation.
• ‍How should I prepare for a diagnostic test?
  Ask ahead of time if you need to fast or avoid certain foods or medicines. Review all prescriptions, over the counter medicines, and supplements that could affect results. Share any allergies or prior reactions to contrast dyes or medicines. Arrange a ride and recovery time if sedation might be used. Wear comfortable clothes and leave jewelry at home for imaging.
• ‍What do sensitivity and specificity mean?
  Sensitivity describes how often a test correctly finds people who have a condition. Specificity describes how often it correctly shows that people without the condition are negative. Your clinician also considers positive predictive value and negative predictive value, which describe how likely a result is to be correct for you given your risk and symptoms.
• ‍Can tests be wrong? What are false positives and false negatives?
  Yes. A false positive happens when a test says you may have a condition that you do not actually have. This can lead to worry and follow up tests. A false negative happens when a test misses a condition that is present, which can delay diagnosis. This is why your clinician looks at test results together with your symptoms and risk factors, and sometimes repeats or confirms tests.
• ‍What is the difference between a screening test and a diagnostic test?
  Screening looks for a condition before you have symptoms, for example mammograms for breast cancer or Pap and HPV tests for cervical cancer. Diagnostic testing investigates a symptom or follows up on an abnormal screening result. A positive screening test usually needs a diagnostic test to confirm the finding.
• ‍How is quality and safety of testing monitored?
  Most clinical laboratories must meet national quality standards for staffing, equipment, and accuracy checks. Imaging facilities also follow safety and practice standards. These systems help ensure that tests are performed reliably and that radiation and other risks are kept as low as reasonably possible.
• ‍What questions should I ask before agreeing to a test?
  Consider asking:
  • What question is this test meant to answer
  • How might the result change my care
  • What are the benefits and risks
  • Are there alternatives that could answer the same question
  • How should I prepare
  • When and how will I get results
  • Will I need repeat testing
  • What will it cost and is it in network for my insurance
  ‍
• What happens after I have the test?
  Your care team reviews the results with your symptoms, history, and any prior studies. Some results lead to watchful waiting and repeat testing later. Others call for treatment, referrals, or more targeted tests. Ask for a copy of your report and keep it with your personal health records.What if coordinating tests feels overwhelming?
  If scheduling, transportation, or follow up is hard, ask for help. Support with appointments, reminders, and communication between clinicians can make it easier to prepare properly, complete tests on time, and understand what to do next.What are the key things to
• remember about diagnostic tests?
  Diagnostic tests answer specific questions and guide care, but they are only one part of the picture. Good preparation and clear communication improve accuracy and safety. Results make the most sense when viewed alongside your symptoms and risk factors, and shared decision making with your clinician helps you weigh benefits and risks in a way that fits your goals.

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

Related Understood Care resources

• Understood Care. Appointments. https://understoodcare.com/care-types/appointments
• Understood Care. Care Coordination. https://understoodcare.com/care-types/care-coordination
• Understood Care. Communication. https://understoodcare.com/care-types/communication

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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.