2 Diagnostic Tests and Procedures
Learn what common diagnostic tests measure, how to prepare patients and collect specimens safely, and how to interpret and respond to results in clinical context.
What Diagnostic Tests Show
Diagnostic tests help detect disease, establish or refine a diagnosis, guide treatment, and monitor a patient’s response. They include laboratory analysis of specimens, imaging, electrical recordings, and procedures that visualize or sample body tissues. A result is one part of the clinical picture and should be considered alongside symptoms, history, examination, and prior results.
Common laboratory tests
A measures blood cells and related components, helping assess concerns such as anemia, infection, and bleeding or clotting.
A measures substances such as electrolytes, glucose, and kidney-function markers; the comprehensive panel also includes selected liver-related tests.
Coagulation tests, including prothrombin time/INR and aPTT, assess aspects of clotting and may help evaluate bleeding risk or monitor certain anticoagulant therapies.
Troponin helps assess heart-muscle injury. ECG/EKG records the heart’s electrical activity, while echocardiography uses ultrasound to create images of the heart.
Urinalysis examines urine for cells and substances. Urine, blood, sputum, wound, and stool cultures can help identify organisms that may cause infection; susceptibility testing may guide antimicrobial selection.
An helps assess oxygenation, ventilation, and acid–base status. Interpret it with the patient’s condition and respiratory support in mind.
Imaging and procedures
X-ray and computed tomography (CT) use ionizing radiation. Magnetic resonance imaging (MRI) uses a strong magnetic field, so implanted devices and metal require screening according to facility procedure. Ultrasound uses sound waves to create images. Contrast material may improve some images; ask about prior contrast reactions and relevant conditions such as kidney disease, and follow imaging-team instructions. Endoscopy may require fasting or bowel preparation, and sedation may affect safety afterward. Biopsy involves sampling body tissue.
Takeaway: Tests provide different kinds of evidence; no single result should be treated as a complete diagnosis.
Preparation and Specimen Collection
Preparation varies by test. First verify the order and patient identity, explain the purpose and steps in understandable language, and check test-specific instructions. Some tests require fasting or other restrictions, but many do not. Review medicines, supplements, allergies, pregnancy possibility when relevant, and previous reactions to contrast or sedation. Do not advise a patient to stop medication unless the responsible clinician directs it. If instructions were not followed, report this before collection because it may affect the result.
Collect and handle specimens carefully
Use the correct container and collection method, avoid contamination, and label the specimen according to policy. Labels typically include patient identifiers, specimen type or source, and collection date and time. Match the label to the patient at the point of collection, complete required documentation, and send the specimen promptly under required storage and transport conditions. These steps protect . If a specimen is mislabeled, compromised, or collected incorrectly, follow policy and arrange recollection when indicated; do not guess or relabel from memory.
Examples of collection practices:
Blood: Use the ordered tubes and collection sequence required by local policy. For blood cultures, careful disinfection and adequate sample volume help reduce contamination and improve detection. Collect before antimicrobials when feasible, without delaying urgent treatment.
: Explain hand hygiene and perineal cleansing. Collect the midstream portion in the sterile container without touching its inside, then transport or store it as directed.
Sputum: When ordered, obtain material coughed from the lungs rather than saliva; follow instructions for mouth rinsing and the specimen cup.
ABG: A trained clinician commonly draws the arterial sample from the wrist. After collection, apply firm pressure and assess for bleeding, following local protocol, especially if the patient takes anticoagulants.
Takeaway: Correct identification, collection, labeling, and handling are essential for a usable result.
Interpreting Results and Taking Action
Use the and units printed on the specific report. Ranges can differ among laboratories and methods. A value inside the interval does not rule out illness, and an out-of-range value does not by itself prove disease.
Interpret findings in context by considering symptoms, baseline values, trends, timing, medicines, and preparation. For example, a mildly abnormal result may have different significance in an asymptomatic patient than in someone who is acutely deteriorating. Review the report’s status—such as pending, preliminary, or final—as well as specimen adequacy and comments. Compare with previous values when useful.
Communicate and concerning changes promptly through the required escalation pathway. Document the result, notification, and actions taken. Never delay urgent assessment or intervention while waiting for a result when the patient’s condition requires immediate care.
Takeaway: Interpret results as part of the clinical picture, not in isolation, and act promptly when findings or the patient’s condition are concerning.
Nursing Responsibilities
Nursing responsibilities extend across the entire testing process.
Before testing: Verify the order and patient identity; assess relevant history, allergies, medicines, and preparation; obtain consent when required; explain the procedure and address questions. For imaging or procedures, confirm screening and readiness, including access to emergency support when indicated.
During testing: Follow infection-prevention and safety practices, protect privacy and dignity, assist with positioning, observe the patient’s response, and promptly report distress or unexpected reactions. Follow scope-of-practice requirements and facility procedures.
After testing: Assess for procedure-specific complications, such as bleeding after an arterial puncture or sedation-related impairment after endoscopy. Provide ordered aftercare and safety instructions, ensure specimens reach the laboratory correctly, track pending results, communicate significant findings, and document care and follow-up.
When a result is unexpected, verify patient and specimen details and promptly consult the responsible clinician rather than interpreting the finding alone. Reliable testing depends on preparation, identification, collection, handling, observation, communication, and timely follow-up.