Intro. to Laboratory Flashcards
What are the purposes of diagnostic testing?
- Diagnosis - rule in or rule out
- Screening - risk factors, occult disease
- Patient Management - severity, course, prognosis, and Rx
Factors to consider when ordering a test.
- History and physical exam findings
- Ability to do something with the results
- Potential advantages, costs, and disadvantages
What is a scope exam (gross pathology exam)? What are some examples?
Visualization of internal organ systems
- bronchoscopy
- colonoscopy
- flexible sigmoidoscopy - distal 2 ft of large intestine
- Esophagogastroduodenoscopy - endoscopic view of stomach and esophagus
- Cytoscopy - in bladder
What type of exam is an x-ray considered in this context?
According to Dr.Bentley, a gross exam.
Uses radiation to detect variations in density of tissue
Examples:
skeletal - fractures
lungs/chest - tumors/lung pathology
abdominal - pathology of kidney, ureters, bladder
What is a myelogram?
X-ray with radio-opaque dye to detect changes
- detects stones, tumors, blockages, spatial changes in bones
What is a CT scan?
X-ray of body tissues in small ‘slices’
- can be done with or without contrast
- contrast usu I, Ba, gastrografin based
- can detect bleeds and small structures
What is an MRI?
Use of magnetic fields to produce cross-sectional images
- good for soft tissue - masses, tears, bleeds, damage to tissues from infection or injury
- Can be done with gadolinium contrast - contraindicated in pregnant or patients with kidney disfunction
What is a biopsy?
A type of cellular path testing
- skin, LN, bone, liver, chest
- small piece of tissue removed and examined histologically
What is a puncture biopsy?
Removal of fluid for analysis
- lumbar puncture
What is a culture and sensitivities (C&S) assay?
Growth of a bacterium from body fluid to identify pathogen and antibiotic that it is sensitive to
- bacterial ‘lawn’ on plate, with antibiotic paper discs, sensitivity determined by diameter of clear agar around a disc
What is a fecal occult blood test?
Small card that indicates presence of blood
- sample obtained during digital rectal exam
- can indicate intestinal neoplasms
What is an ultrasound?
Use of sound waves to detect movement and fxn of organs
- no radiation exposure
Examples:
- carotid, venous, abdominal, echocardiogram, and fetus
Doppler - use of sound waves to detect abnormal blood flow in aa or veins
What is an electrogram?
Test for electrical activity of a tissue
- EKG, nerve conduction studies
What is an angiogram?
Use of radio-opaque dye to detect blockages
- diffuses through pertinent structures
- cardio, pulmonary, and lower extremity angiograms
Examples of organ-specific function testing.
- Ventilation perfusion scan
- Pulmonary function test
- Endoscopic retrograde cholangiopancreatography
- Percutaneous transhepatic cholangiography
- Ba swallow
- kidney radionucleotide scan
- DEXA
What is a CBC?
Complete Blood Count
- corresponds with anemias, infections, malignancies
Includes:
- leukocytes (WBCs)
- Erythrocytes (RBCs)
- Hemoglobin (HgB)
- Hematocrit (HCT)
What changes levels of hemoglobin?
Increase - dehydration, burns, vomiting, polycythemia, extreme physical exercise
Decrease - all anemias, hypothyroidism, B12 and folate deficiencies, chronic disease
What changes levels of hematocrit?
(ratio of volume of RBCs to tot vol of blood)
Increase -high altitude, smokers, tumors, polycythemia vera, heart disease
Decrease - anemias, acute of chronic blood loss, hemolysis, dilutional, alcohol, drugs
What changes WBC levels in a CBC?
Usu make up 1% of tot blood volume
- alterations due to infections, hemotological malignancies, leukemias, lymphomas, steroid use, anemias, drugs and sepsis
What is a CBC with a differential?
Breakdown of leukocytes according to cell type and number
Neutrophils: PMNs usu 60% of leukocytes
Explain left shift versus right shift in a CBC w/ diff.
Left shift - immature cells predominate, indicates bact inf, toxemia, hemorrhage
Right shift - mature cells predominate, indicates liver disease, megaloblastic anemia, iron def disease
What can lymphocyte levels in a CBC indicate?
Usu 30% of leukocytes
- increases in viral disease, acute and chronic lymphocytic leukemias, immune disorders
What can eosinopil levels in a CBC indicate?
NAACP - neoplasm, addison’s disease, allergy, collagen vascular disease, parasites
What can basophil levels in a CBC indicate?
increased - lymphoproliferative disorders, particularly chronic myelogenous leukemia
What does prothrombin time test for?
Used to assess coag pathway forming blood clots
- standardized to INR
- very sensitive to vitamin k dep factors and liver disease
When using warfarin/blood thinners use INR to assess efficacy/titrate dose - should be 2-3x normal
What does a peripheral blood smear test for?
Evaluate morphology of blood cells Detects: - malaria - microcytic hypochromic anemia - lymphoblasts - Basophilic stippling (Pb poisoning, thalassemias)
What is a basic metabolic panel and what does it test for?
Measures levels of noncellular elements of the blood, levels affected by different diseases
- Na+
- Cl-
- HCO3- (buffer)
- K+ (nerve excitation, mm contraction, myocardial potential)
What is a blood glucose test?
Indicates variety of metabolic disorders if it falls outside normal fasting range of 7-100 mg/dL
What is a hemoglobin A1c test for?
Measures levels of blood sugar over life of a circulating RBC - 6 weeks
- 6 week timeline to monitor blood sugar levels, diabetes control
- Fe deficiency anemia can elevate A1c levels
What is a renal function study?
Measure of BUN and creatine levels
- BUN:Cr ratio is used to id source of pathology
BUN:Cr
>20:1 = prerenal
10-20:1 = normal
<10:1 = intrarenal
What do bilirubin levels indicate in liver function tests?
- mostly derived from breakdown of heme
Total: increased with hepatic damage, biliary obstruction, hemolysis
Direct, conjugated: increased with biliary obstruction, Dubin-Johnson syndrome, Rotor Syndrome
Indirect, unconjugated: caused by hemolysis, decreased hepatic uptake
What do liver function enzymes indicate in a liver function study?
Alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkalophosphatase (alk phos), and gamma glutamyl transferase (GGT)
Indicates malignancies, alcohol abuse (chronic), liver disease
What does C-reactive protein indicate?
Acute phase, short half life
- indicates inflammation or tissue injury, particularly with MI
What does a lipid panel indicate?
Total, with LDL and HDL and LDL as well as tot triglycerides
- important indicators about diet, health, and risk factors for CV disease
What do thyroid studies measure?
TSH levels - thyroid stimulating hormone
- secreted by pituitary, induces secretion of thyroxine from thyroid gland
- important regulator of metabolism
- high in hypothyroid patients
Explain what urine analysis tests for and how it is performed.
Dipstick test
Evaluates:
- appearance - cloudy, foamy, etc.
- specific gravity
- blood
- ketones
- protein
- nitrites
- leukocyte esterase
