Intro to Lab Medicine Flashcards
Discuss the issues of infection control and Universal Precautions as they pertain to the performance of diagnostic testing
When running diagnostic tests such as blood draws, it is important to maintain sterility of the fluid being drawn as well as keeping the healthcare work safe from blood born pathogen exposures.
- Wear gloves when drawing blood - Wash hands after drawing blood - Wear eye protection - Wear a gown if there is a situation where there is a large amount of blood exposure
Accuracy
How closely the test results correspond to the ‘gold standard’
How often is the test right?
Precision
How reproducible the results are with repeat testing of the same specimen
Specificity
Percent of persons without disease of interest with negative test results
SPIN
TP / TP + FN
Sensitivity
Percent of persons with the disease of interest who have positive test results
SNOUT
TN / TN + FP
Predictive Value
Estimation of probability of presence or absence of disease; derived from test’s sensitivity, specificity, and prevalence of the disease in the tested population
Positive PV (PPV)
Percent of persons with positive test results who have the disease
TP / (TP + FP) x 100
Negative PV (NPV)
Percent of persons with negative test who do not have the disease
TN / (TN + FN) x 100
False Positive
Erroneous test result that indicates presence of a disease that does not exist
False Negative
Erroneous test result that failed to recognize an existing disease
Prevalence
Number of cases of disease in a population
Likelihood Ratio
How likely the test is to be helpful
+ LR
> 1; associated with the disease and is helpful to rule in
Sensitivity / 1 - Specificity
- LR
Pretest Probability
Proportion of people in population at risk who have the disease at a certain time
Probability the patient has the disease before test is performed
Posttest Probability
Proportion of patients testing positive who truly have the disease
Patient based probability of having disease (likelihood ratio translates pretest into posttest)
Significance of reference ranges (NONE)
- Reference Range: statistically derived numerical range for lab values based on a sample of individuals assumed to be healthy.
- Standard parameters for a reference range are +/- 2 SD
- Age, sex, and population groups can affect reference ranges significantly.
Examples of affected reference ranges (NONE)
- Pediatric patients may have lower reference ranges due to physiological immaturity.
- Geriatric patients are difficult to establish a reference range because of their wide variety of health status and disease states. (Some reference ranges are unchanged, some are changed with no clinical significance, and some are changed with clinical significance)
- X-linked and autosomal enzyme deficiencies
- Sickle Cell
Common sources of error that can affect the quality of lab tests
- Lab processing or equipment errors
- Deteriorated reagents
- Calibration errors
- Calculation errors
- Misreading results
- Mis-entry of data/other documentation errors
- Improper sample preparation
- Improper specimen handling- collection, transportation, refrigeration
- Time course of specimen collection
Major reasons for ordering a lab measurement
Screen, Diagnose, Manage disease
Labs to screen
Screen for treatable conditions in pre-symptomatic individuals
Labs to Dx
Diagnose disease in symptomatic individuals
o Discover occult disease
o Confirm suspected Dx
o Determine stage, activity, severity of disease, or progression of disease
o Detect recurrence of disease
Labs to manage
Manage disease in individuals already diagnosed o Guide the course of therapy o Assess effectiveness of therapy o Drug levels o Side effects
Pros of profile testing
Often less costly to group lab tests together
Cons of profile testing
Unnecessary patient data is often generated. You want to use the most cost effective, sensitive, and specific measures when deciding between panel or single test ordering. Panel selection: based on availability of panel and appropriate medical staff consultation.
Significance of order STAT tests
- STAT tests = rapid turnaround rate of the results
- Used in emergency situations where the test result are needed immediately
- Given high priority in the lab
Results that indicate PANIC or Critical values
STAT test results have a critical value (PANIC) meaning they indicate potentially dangerous conditions which require immediate attention by the clinician.
CLIA
Clinical Laboratory Improvement Amendments
CLIA Waived Tests
Those that pose no risk of harm to the patient if used incorrectly or use such simple and accurate methodologies that inaccurate results are unlikely
CLIA Provider Performed Microscopy Test (PPM)
o Must be performed by a physician or a mid-level practitioner during the patient visit
o Moderate complexity category
o Primary instrument is a microscope
o Specimen must be labile (or delay in testing could compromise the accuracy of the test)
o Control materials are not available to monitor the entire testing process
o Limited specimen handling is required
o Examples: KOH preps, UA micro only, semen analysis, nasal smears
Dipstick Urinalysis
- Strip is placed in the urine sample, chemical reactions cause color changes that are compared to a key
- Measures pH, specific gravity/concentration, protein, sugar, ketones, bilirubin, evidence of infection & blood
Fecal Occult Blood Test
- Tests for stool in the blood, may indicate colon cancer
- Recommended annually after 50
- Positive result requires follow up colonoscopy)
Urine Pregnancy Test
- Measure presence of hCG, hormone produced by the placenta
- Can be detected several days to two weeks after conception
- Positive result is confirmed with blood test
Erythrocyte Sedimentation Test
ESR
- ESR, used to detect inflammation
- Non-specific or diagnostic
- Can be used to monitor disease and response to therapy
Spun Hematocrit
- Measurement of RBC count (RBC should make up 37 – 49% of blood)
- Typically part of a CBC
- Used to detect anemia, not diagnostic
Wet Mount
• Micro exam of vaginal discharge for bacterial vaginosis, candidiasis, trichomoniasis, increased WBC
Potassium Hydroxide (KOH) mount
- Micro exam of skin, hair, nail, vaginal discharge, or body fluids for fungal elements
- Confirms presence, not species
Pinworm prep
- Clear tape applied to anal area in early morning, eggs on skin surface will stick to tape and can be identified under microscope
- Should be done three days in a row
Capillary Blood Glucose (CBG)
- Used to monitor diabetes control
- Drop of blood from finger stick is placed on a glucometer strip
- Values are used to determine insulin dose
Ovulation Test
- Measurement of LH, levels surge during ovulation
- Monitored with menstrual irregularities, infertility, suspected menopause, low testosterone levels in males
- Can indicate developmental abnormalities in children
