Laboratory and other diagnostic testing is part of assessment. Diagnostic tests are used to (1) identify risk factors for disease; (2) diagnose a medical disease; and (3) manage a client’s illness. Nurses teach clients about specific tests, including their purpose, preparation needed, and after-test care. They also schedule tests, prepare clients, ensure client safety, assist with data collection, perform procedures, and document client reactions. Diagnostic tests can be noninvasive, in which the body is not entered with any type of instrument, or invasive, in which the body is accessed through some type of instrumentation procedure.

Prior to diagnostic testing, the nurse ensures client safety by making sure the client is wearing an arm band, taking baseline vital signs, identifying known allergies, assessing the effectiveness of teaching, and notifying the practitioner prescribing the test of any problems. During the diagnostic test, the nurses use “standard precautions” to prevent the spread of infection, using gloves and gowns, if necessary, and labels specimens with the client’s name, the client’s room number, the date, the time, and the source of the specimen. The nurse also provides pain relief and monitors the client’s reaction during the procedure. Nurses with additional education and skills monitor clients receiving conscious sedation, a minimally depressed level of consciousness during which the client retains the ability to maintain a continuously patent airway and respond appropriately to physical or verbal stimuli.

Nursing care after diagnostic testing depends on whether anesthesia was used and, if so, the level of anesthesia used, whether local (client loses sensation to a localized body part), regional (client loses sensation in an area of the body), or general (client loses all sensation and consciousness). Some procedures require the nurse to monitor vital signs and other signs and symptoms. For example, kidney tests may require the nurse to monitor intake and output or to observe for hematuria (blood in the urine). Clients are also given written instructions for care after some diagnostic tests.

Common laboratory tests measure how many analytes (substances or solutes dissolved in a solute) are in a specimen. They are used to detect risk for disease, establish or exclude a medical diagnosis, assess the severity and prognosis of a disease, guide in the selection of interventions, monitor the client’s progress, and monitor the effectiveness of treatment.

The clinical value of a test is related to its specificity, sensitivity, incidence, and predictive value. Sensitivity is the likelihood that a diseased client will have a positive result. Specificity is the likelihood that a healthy individual will have negative results. Incidence is the prevalence of a disease in a population or community. Predictive value is the ability of a screening test to correctly identify the disease state. Laboratory test results are based on normal range values established in the International System of Units (SI). Laboratory test values are affected by several factors, such as age, gender, weight, diet, medications, activity, smoking, alcohol, or time of day.

Accuracy of laboratory testing requires the nurse to transcribe the practitioner’s order accurately, complete all information on forms completely and accurately, include pertinent data (medications, etc.), collect the correct specimen from the correct client, and place the test results on the correct chart. Point of care testing (POCT) is common in critical care settings to improve cost-effectiveness and quality. POCT involves collecting specimens and performing the test analysis at the bedside.

Common blood specimen collection methods include venipuncture, arterial puncture, and capillary puncture. Venipuncture (collection of blood from a vein) can be performed by phlebotomists (individuals who perform venipuncture), nurses, and other health professionals. Health care workers need to take care to prevent needle-stick injury to themselves due to the risk for contracting human immunodeficiency virus (HIV) and hepatitis. The common blood tests are the red blood cell count, hemoglobin, hematocrit, white blood cell count, the sickle cell test, and type and crossmatch test. The common blood chemistry tests are blood glucose, electrolytes (sodium, potassium, calcium, chloride, magnesium, and phosphate), enzymes, and blood lipids (fats).

Arterial puncture is used to assess arterial blood gases (ABG), including partial pressure of oxygen (PO2), carbon dioxide (PCO2), and the pH of arterial blood. Blood gases are used to evaluate oxygenation, ventilation, the effectiveness of respiratory therapy, and the acid-base level of the blood. Arterial blood samples are collected with a heparinized syringe to prevent clotting, and the specimen is placed on ice. Arterial samples are contraindicated in clients who are on anticoagulant therapy, have clotting disorders, have peripheral vascular disease, or have a negative Allen test (a measure of collateral circulation).

Capillary puncture is performed in the heel, fingertip, or earlobe to obtain small quantities of capillary blood. Capillary puncture is most commonly performed for blood glucose analysis. Blood access for laboratory tests is also available through central lines and venous access devices (VAD), which are primarily used for intravenous therapy and medication infusion, and through implanted ports (port-a-caths). Blood should not be collected through ports used for IV infusions or medications.

Urine specimens are collected randomly (“routine analysis”), as a 24-hour period collection, from a closed drainage system, or as a clean-voided (clean-catch or midstream) specimen. Random urine analysis (UA) can be collected at any time in a clean cup. The nurse should wear gloves when handling the specimen, seal the specimen tightly in a biohazard bag for transport, label the specimen accurately and completely, and take the specimen to the laboratory immediately to prevent the growth of bacteria or changes in the substances in the urine.

For timed (24-hour) urine specimen collection, the nurse instructs the client to void at the beginning of the test in a clean container, discarding the first specimen. Subsequent clean specimens are placed in the 24-hour specimen jug, which is refrigerated or kept on ice as it is collected. Care is taken to allow only clean urine in the 24-hour jug, not feces or toilet paper. Urine collected from a closed drainage system is obtained through a port in the indwelling Foley catheter. The inside of the Foley catheter is considered sterile. Urine should not be collected from the closed urine bag, which is not sterile. A clean-voided specimen is done to produce an uncontaminated sample. The clean-voided specimen should be collected first thing in the morning, after cleansing around the meatus. Female clients cleanse the perineum from front to back and male clients cleanse from the tip of the penis downward. The common urine tests are urine pH, specific gravity, glucose, protein, and blood cells.

Stool specimens are collected for either a one-time defecation or over 24, 48, or 72 hours. The most common stool tests are for leukocytes, blood, fat, ova and parasites, and pathogens. A specific test for infections is the culture and sensitivity test. Culture refers to the growing of microorganisms to identify the pathogen. Sensitivity tests help the practitioner select appropriate antibiotic therapy.

The Papanicolaou test (smear method of examining stained exfoliative cells) evaluates the cells in a tissue, usually from the cervix. Pap smears are indicated for any woman over the age of 40 having a family history of cervical cancer, or with previous positive tests. Radiology (x-ray) studies help the practitioner form a diagnosis or determine whether further tests are necessary. Some x-rays require a contrast medium, such as barium or iodine, to improve visualization. Common x-rays are chest x-rays, kidney-ureter-bladder (KUB) x-rays, upper and lower gastrointestinal x-rays (using a barium contrast), mammograms, and skeletal x-rays.

Cardiovascular x-rays include angiography, which evaluates blood flow and identifies aneurysms; arteriography, which assesses problems in arteries; cardiac catheterization, in which problems are identified in the coronary vessels; digital subtraction angiography to diagnose vascular malformations; lymphangiography, to study the lymphatic system, and venography, to study the venous system of the lower extremities. Dye injection studies include cholangiography, the radiographic study of the biliary system; cystography, a radiographic study of the urinary bladder; intravenous pyelogram (IVP, radiographic study of the kidneys, ureters, and the bladder); bronchography, the radiographic study of the trachea and bronchi; and myelography, the radiographic study of the spinal cord. Ultrasonography is a noninvasive study using high-frequency sound waves to visualize deep body structures, such as the heart (echocardiogram) and peripheral vessels. Electrodiagnostic studies include the electrocardiogram (ECG or EKG), a graphic recording of the heart’s electrical activity, and electroencephalogram (EEG), the graphic recording of the brain’s electrical activity.

Computed tomography (CT) scans are radiological tests that transmit data to a computer, which can then manipulate quantitative measurements and multidimensional images. Magnetic resonance imaging (MRI) is the visualization of body organs through the interaction of hydrogen atoms in the body placed in a magnetic field.

Endoscopy is the visualization of a body organ or cavity through a scope. Examples include arthroscopy (knee), bronchoscopy (bronchi), colonoscopy (large intestine), colposcopy (cervix and vagina), cystoscopy or cystourethroscopy (urinary bladder and ureters), esophagogastroduodenoscopy (esophagus, stomach, and upper duodenum), laparoscopy (peritoneal cavity), and proctosigmoidoscopy (rectum and sigmoid colon). Aspiration and biopsy includes withdrawing fluid to obtain a specimen and excising a small amount of tissue for further examination. Common aspirations are amniocentesis (withdrawal of amniotic fluid), bone marrow aspiration and biopsy, paracentesis (aspiration of abdominal fluid), thoracentesis (aspiration of thoracic fluid), and cerebrospinal fluid aspiration.