Intro to Lab Medicine Flashcards by Kaylee Gescher

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

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Accuracy

How closely the test results correspond to the ‘gold standard’
How often is the test right?

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Precision

How reproducible the results are with repeat testing of the same specimen

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Specificity

Percent of persons without disease of interest with negative test results
SPIN
TP / TP + FN

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Sensitivity

Percent of persons with the disease of interest who have positive test results
SNOUT
TN / TN + FP

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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

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Positive PV (PPV)

Percent of persons with positive test results who have the disease
TP / (TP + FP) x 100

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Negative PV (NPV)

Percent of persons with negative test who do not have the disease
TN / (TN + FN) x 100

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False Positive

Erroneous test result that indicates presence of a disease that does not exist

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False Negative

Erroneous test result that failed to recognize an existing disease

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Prevalence

Number of cases of disease in a population

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Likelihood Ratio

How likely the test is to be helpful

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+ LR

> 1; associated with the disease and is helpful to rule in

Sensitivity / 1 - Specificity

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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

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Posttest Probability

Proportion of patients testing positive who truly have the disease
Patient based probability of having disease (likelihood ratio translates pretest into posttest)

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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