Chapter 34 Diagnostic Testing PDF

Preview

Summary

Normal Structure and Function of Blood Cells On average, a person has approximately 5 liters of blood circulating throughout the body. Approximately 3 liters are plasma, the fluid portion, and 2 liters are cells. Cell types: Three types of cells are found in blood: ‣ **erythrocytes** - ( **red blood...

Description

! Normal Structure and Function of Blood Cells • On average, a person has approximately 5 liters of blood circulating throughout the body. !

transport to and carbon dioxide transport from the erythrocytes! • RBCs have important role in maintaining acid-base balance ! • Development of erythrocytes occurs in bone marrow! ‣ thrombocytes - (platelets) integral part of blood clotting! • When blood vessel ruptures, platelets clump together to form a plug to seal the vessel ! • Platelets are formed in the bone marrow! ‣ leukocytes - (white blood cells) responsible for the inflammatory and immune response !

• Plasma:

pressure in the blood ‣ fibrinogen - plays an integral part in blood coagulation by converting into fibrin threads in the presence of ionized calcium! • Essential component of blood clots ‣ globulins - classified as alpha, beta, and gamma globulins! • Some globulins function as antibodies, and others are responsible for enzymatic functions and the transport of lipids, iron, and copper in the blood.!

Laboratory Tests: Blood • Complete blood count

• Coagulation studies

‣ This vasoconstriction lasts only a few minutes but provides the needed time and decreased surface area to facilitate platelet aggregation. ! ‣ The platelets clump together and form a temporary plug to seal the injured vessel. ! ‣ The final mechanism to protect against blood loss is coagulation, or clotting, of the blood.! • This complex process involves the conversion of fibrinogen to fibrin. ! • The fibrin then adheres to the platelets and other blood cells to form a more permanent seal to the injured blood vessel!

• Blood chemistry

‣ cations (positively charged) - sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+)! ‣ anions (negatively charged) - chloride (Cl−), bicarbonate (HCO3−), and phosphate (HPO4−)!

‣ Excess glucose is converted to glycogen and stored in the liver.! ‣ Normal glucose levels are controlled by the release of two hormones: ! • glucagon - raises blood levels of glucose by facilitating the breakdown of glycogen! • insulin - lowers blood glucose levels by acting as a carrier to transport glucose into the cells, where it is available for use.!

‣ The most common is diabetes mellitus.! ‣ Blood glucose levels can be monitored with a venous sample, but it is most frequently monitored using a capillary blood sample before meals and at bedtime for patients with diabetes.! ‣ The American Diabetes Association states that diabetes is diagnosed for Hgb A1c levels more than 6.5%. ! • A level of < 7% indicates a diabetic in good control;! • > 9% indicates that the patient has had poor blood glucose control and increases the patient's risk of long-term complications from hyperglycemia • Kidney function tests

‣ blood urea nitrogen (BUN) - Elevated BUN levels may indicate decreased renal glomerular function. BUN levels also may be elevated as a result of a high-protein diet or with dehydration.! ‣ serum creatinine - a waste product of skeletal muscle metabolism! • The normal ratio of BUN to creatinine is between 6 and 25.!

‣ A level less than 60 mL/min/1.73 m2 is a sign of renal impairment.!

‣ A level below 60 mL/min/1.73 m2 indicates renal impairment. • Lipid profile

%

%

‣ low- density lipoprotein (LDL) cholesterol - transport % % cholesterol from the liver to various parts of the body. ! • LDL cholesterol is considered “bad cholesterol” because of its role in atherosclerotic disease.! ‣ high-density lipoprotein (HDL) cholesterol - transport %% excess cholesterol from the tissues back to the liver, where it is broken down and excreted in bile. ! • HDL cholesterol is considered “good cholesterol,” because high levels reduce the risk of heart disease.! ‣ triglycerides - composed of fatty acids, proteins, and glucose. ! • They are synthesized in the liver and stored in adipose tissue and muscle. ! • They can be retrieved when additional energy is needed to meet metabolic demand.! • Measurement of triglycerides is used to calculate LDL cholesterol levels with the following formula: !

hormones, and sex hormones. • Liver function tests

‣ ‣ ‣ ‣

alanine aminotransferase (ALT) alkaline phosphatase (ALP) aspartate aminotransferase (AST) gamma-glutamyl transpeptidase (GGTP)

colloidal oncotic pressure in the vascular and extravascular spaces. ! ‣ Low levels of albumin may indicate malnutrition.!

precise measure of current nutritional status.!

or RBC destruction. Total bilirubin levels are increased in jaundice.!

production. Serum levels are used to monitor liver disease progression and the effect of hepatotoxic drugs.!

indicators of liver and bone disease.!

• Cardiac markers

• Elevated CK levels usually indicate damage in one of these three areas.! • CK is further broken down into three isoenzyme forms. !

‣ CK-MB isoenzyme! ‣ Myoglobin - oxygen-transporting and storage protein found in cardiac and skeletal muscle. ! • When damage to a muscle cell occurs, myoglobin is released, and blood levels of the protein rise. ! • Because myoglobin is found primarily in cardiac and skeletal muscles elevated levels can be diagnostic of

myocardial infarction (MI) or skeletal muscle trauma.! ‣ troponin I and troponin T - found exclusively in cardiac muscle. ! • These proteins are released during myocardial damage and can be detected as early as 4 hours after an MI, even with small areas of cardiac muscle injury!

‣ Normal levels for homocysteine are 4 to 14 μmol/L. ! ‣ High levels of homocysteine are associated with an increased risk of cardiovascular disease, although it is not known whether increased levels are a precursor to or a result of the disease. ! ‣Smoking and vitamin deficiencies, specifically folate and vitamins B6 and B12, seem to play a role in elevating levels.! • Adding these vitamins to the diet can lead to lower serum levels of homocysteine.!

excretion and urine output. Elevated levels are often found in patients with heart failure, and plasma concentrations reflect the severity of cardiac failure. Normal levels are below 100 mg/mL.!

inflammatory bowel syndrome. CRP is a marker for vascular inflammation—an important factor in atherosclerosis. The highsensitivity CRP (hs-CRP) blood test is used to measure the CRP level. Levels below 1 mg/L indicate a low risk, levels between 1 and 3 mg/L indicate average risk, and levels above 3 mg/L indicate high risk. CRP is now used as a screening for coronary artery disease and as a predictor of future cardiac events.!

!

Laboratory Tests: Urine and Stool • Urinalysis

renal system. !

• Stool

fecal fat, urobilinogen levels, and ova and parasites.!

pancreatic enzymes, or deficiency of bile (usually due to biliary obstruction).!

‣ Normal levels are 50 to 300 mg per 24 hours. Increases in urobilinogen result from increased RBC destruction, as in hemolytic anemia. ! ‣ Decreased levels are seen in biliary obstruction or in severe liver disease.!

‣ With the exception of pinworms, common parasites are ingested by consuming contaminated food or water. • Culture and sensitivity

‣ After the pathogen has been identified, it is exposed to various antibiotics, and the bacterial growth is monitored to determine sensitivity, or which antibiotic therapy would be most effective in treating the infection. ! • Bacteria are considered susceptible when the antibiotic kills or inhibits growth, whereas resistant bacteria continue to grow despite the presence of the antibiotic.

Diagnostic Examinations • Radiography - the use of x-rays to visualize bones, organs, and soft tissues for abnormalities.!

‣ High-density matter, such as bone, appears to be white, and air-filled areas appear to be black. examination.! • Chest x-rays are one of the most frequently ordered radiographs. A chest x- ray can be used to diagnose several pulmonary disorders, such as tuberculosis, cancer, and pneumonia. Chest x-rays are also used to determine the correct placement of treatment devices, such as chest tubes, central line infusion catheters, and pacemakers.! • X-rays are used to diagnose fractures in bones and joints. Other disorders that can be diagnosed with orthopedic x-rays include osteoporosis, osteomyelitis, arthritis, and tumors. A frontal supine x-ray of the abdomen is called a KUB, which stands for kidneys, ureters, and bladder.!

• The ideal contrast material has low toxicity, is nonallergenic, has no effects on normal physical function, and is relatively low in cost. ! • All contrast materials have the potential for causing allergic reactions, ranging from mild responses (e.g., nausea, vomiting, localized rash) to severe anaphylaxis. ! ‣ An intravenous pyelogram is a contrast x-ray exam that examines the kidneys, ureters, and bladder and is useful for diagnosing kidney stones and other abnormalities of the urinary tract.! ‣ The upper GI series consists of a series of x- rays of the esophagus, stomach, duodenum, and upper portion of the jejunum. ! • It is useful for diagnosing gastric ulcers, pyloric stenosis, hiatal hernias, and carcinoma of the stomach. ! • Before the examination, the patient drinks a contrast agent, usually barium sulfate; the upper GI series is sometimes referred to as a barium swallow. !

• The contrast medium is introduced through a rectal tube or an enema. ! • Examination of the ascending, transverse, and descending colons, as well as the sigmoid colon and rectum, is useful in diagnosing colon cancer, obstructions, and chronic disorders (such as ulcerative colitis). ! ‣ For the upper and lower GI barium studies, it is the nurse's responsibility to monitor the patient until the barium is expelled. Patients should increase their fluid intake afterward, and some may need a mild laxative to aid in the elimination of the barium. The patient should be aware that barium can cause white stools for a few days as it is expelled. • Computed Tomography

• Magnetic Resonance Imaging

magnet and radio-frequency waves that cause hydrogen nuclei to emit signals. A computer translates the signals into a well- defined image of the structure.! ‣ MRI produces a cross-sectional image of the body, similar to a CT scan, but without radiation exposure. It allows better visualization of blood vessels and signs of hemorrhage within hours of the event.! ‣ Because the magnet can move metal objects implanted in the body, it is contraindicated for patients with pacemakers, implanted medication pumps, inner ear implants, fragments from gunshot wounds, or other metal objects in the body. All jewelry must be removed before the test. • Positron Emission Tomography

‣ PET scans are commonly used to study the brain, heart, and in oncology to identify pathologic tissue. • Electrocardiogram

cardiac muscle. !

depolarization), and T wave (ventricular repolarization).! ‣ Increases in the duration of any waveform can indicate injury to or disorders of the cardiac conduction system. • Endoscopy

‣ Endoscopic examination is often used to identify tumors and to remove tissue samples for biopsy.!

• Ultrasound visualization of soft tissue organs by recording and measuring the reflection of ultrasonic waves. • Needle aspirations and biopsies

to remove fluid and tissue for testing. !

samples with minimal trauma to the underlying organ or structure.!

Assessment:

Implementation and Evaluation: • The nurse's responsibility during a diagnostic procedure is to monitor the patient and assist the PCP. ! • A time-out must be called prior to any procedure to properly identify the correct patient with the correct procedure and correct site. ! • Post procedure, the nurse's responsibility is to monitor vital signs and assess for any complications that may arise from a procedure (hemorrhage, pain, allergic reaction, and infection).! • The nurse makes sure that each specimen is placed in the appropriate container and clearly labeled with the patient's identification information. The date and time of the collection and site/location should also be noted on the label.! • Specimen collection

which collects capillary samples ‣ Venipuncture - purpose of the test is to monitor blood levels of a medication, venipuncture must be done at a precise time after the medication is administered! ‣ Venipuncture is an invasive procedure that may expose the nurse to blood- borne organisms and contaminated needles. The nurse must wear gloves throughout the procedure and properly dispose of the collection needles in the sharps container immediately after the specimen is obtained.! ‣ Other factors that can influence test results: ! • Hemoconcentration - an increased concentration of RBCs compared with plasma volume, can result from the tourniquet being applied for too long. The nurse should minimize the time that the tourniquet is on the patient's arm and release it as soon as the specimens are collected.! • Hemolysis is the breakdown of RBCs and the subsequent release of hemoglobin. Hemolysis occurs when the needle used for venipuncture is too small and the RBCs are damaged as a result of the negative pressure.! ‣ A high amount of variance in blood collection practices causes concern for quality and patient experience outcomes. Standardization in blood collection processes will improve safety.

methods and standardized processes.! ‣ It is important to assess the venipuncture site in patients who are on anticoagulant therapy (e.g., warfarin, heparin, enoxaparin) or take aspirin on a daily basis. They are at higher risk for continued bleeding. ‣ Blood glucose monitoring device • A drop of capillary blood is obtained by puncturing the end of a finger with a sterile lancet. ! • A test strip with a specific reagent is placed in the monitoring device and the drop of blood is placed on the test strip. ! • The devices use a light beam or an electric charge to interpret the changes on the test strip.

information about renal function, fluid balance, and the existence of infection and other disorders.! • It is essential that the nurse maintain standard precautions when collecting urine and stool specimens. These precautions include washing hands before and after collection, wearing gloves during the procedure, and storing the specimen in a biohazardous material container or plastic bag during transport to the laboratory.

it. Specimens that are cultured to detect, for example, bacterial or viral infection require only a small amount of stool.! ‣ Testing for ova and parasites usually requires a larger sample, typically 1 inch of solid stool or 15 to 30 mL of liquid stool.

‣ A sputum culture is often ordered when an infectious disease (such as pneumonia or tuberculosis) is suspected.! ‣ Subsequent sputum specimens can be used to evaluate the effectiveness of antibiotic or antiviral therapy. ! ‣ Sputum analysis can identify abnormal cells that may indicate a tumor or malignancy.! ‣ The nurse should provide clear instructions to the patient to ensure that the specimen is sputum and not saliva.

exists and the source of that infection, and to determine optimal treatment options.! ‣ Obtaining a throat culture should not be delegated to unlicensed assistive personnel (UAP).

‣ Obtaining a sample of the drainage for culture is an important step in identifying the presence of an infection and determining appropriate treatment. • Interventions after invasive procedures

• Communication and results!

management tools are applied to support safe processes of care, such as the flagging or alerts of abnormal results. Nurses should ensure prompt communication of results to appropriate interprofessional...