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What does standard precautions mean?

Treat all human blood and certain body fluids as if they were known to be infectious for HIV, HBV, HCV and other blood borne pathogens.


What is laboratory medicine?

Encompasses testing services and associated practices for the assessment, diagnosis, treatment, management, or prevention of health-related conditions


What are laboratory tests?

Include any test or examination of materials derived from the human body for the purpose of making patient care decisions and improving public health


What are the 8 clinical purposes of lab testing?

Risk assessment
Establishment & support & exclusion of a diagnosis
Determination of individualized therapy
Assessment of disease progression/response to therapy


What is screening, why is it important, and what are some examples?

Trying to understand that an illness/process exists before there are Ssx.
Individual/Public health
i.e. pap smear, PSA, TB, HIV, etc


What is the immediate & ultimate purpose of a screening test?

IM: classify ppl as being likely/unlikely to have disease (not diagnosis!)
UL: reduce mortality/morbidity


What is the phenomenon of disease?

Dx is a process that unfolds over time. Do not just go from well to dead.
Natural Hx: sequence of developments from earliest pathological change to resolution of dx or death.

i.e. obesity -> fatty liver -> NASH -> cirrosis -> HCC


What is induction, incubation, & latency?

IND: time before you had disease, but you already have risk factors

INC: infectious – time after exposure but before you are clincially symptomatic

LAT: have disease, but no clinical symptoms, before diagnosis


Why is natural hx central to screening tests?

Pre-dectectable -> Detectable -> Clinical -> Disability/Death

During detectable stage (in mid 30s) is when you can screen for a disease
During clinical stage (mid 50s) is when you can see Ssx of dx

W/screening you can intervene 20 years earlier (20 year lead time - only good if there is evidence showing early detection decreases neg. outcomes)


What are the 4 requirements of a good screening program?

1. Suitable dx: serious consequences if untreated, detectable b4 Ssx, better outcomes if tx begins b4 clinical diagnosis

2. Suitable test: detect during pre-ssx, safe, accurate, acceptable/cost-effective

3. Suitable program: reaches target pop., quality control, good f-up of +, efficient

4. Good use of resources: cost of screening/f-up/tx, benefits vs. alternatives


What is reliability?

Get the same result every time. Repeatability. Each time, from each instrument, from each rater.


What is validity?

get the correct result every time


What is sensitivity/specificity?

SEN: probability of correctly classify cases (+ results should mostly have condition), cases found +/all + cases, high is good

SPE: probability of correctly classify non-cases (- results should not have dx), non-cases/all non-cases. True negatives.


When would you choose sensitivity/specificity?

SEN: "HIV test", risk associated w/failure to diagnose HIV is high, FN unacceptable (infectious dx, good tx to fix it early on)

SPE: Cystic fibrosis, dx potentially fatal, no tx besides supportive care is available, FP unacceptable


What is predictive value?

Probability of those tested who are correctly classified into their dx status. How the incidence of disease, affects how many ppl will be falsely placed.

PPV = TP/all + test results
NPV = TN/all - test results

Want this number to be high, increase it by increasing the population prevalence rate (narrowing down your same pop.)


What are 4 ways to establish a diagnosis?

Hypothesis deduction, Medical algorithm, rifle/shot gun, Pattern recognition


Give an example of hypothesis deduction?

Based on Ssx and PE you narrow down what the dx could be and order tests that would separate out the 2-several conditions.


Give an example of rifle/shot gun?

Worried about missing a dx you order every test you can and put the family through more stress than necessary


Give an example of pattern recognition?

Results from a test alone do not give a diagnosis, but several results together paint a symptom picture with a diagnosis involved.


Give an example of medical algorithm?

decision tree - choose one answer and it leads to something else


How do you determine a prognosis?

After diagnosis, based on the likely outcomes of your pt pop and the presentation within that individual pt. Order tests and labs that will give you that info. Tells them what they can expect from the dx and helps mold your tx plan.


What is a reference range?

Cutoff value for a test that distinguishes individuals with a disorder or disease from healthy individuals. 2 SD = cutoff (5% will test out of range and not have dx)


What are factors to consider when working w/ reference ranges?

-Sml but definite grp of clinically norm. ppl may have undetected dx
-Norm ranges are calculated sometimes from too sml of pop sample
-Pop tested for norm range may not be representative of pop to be tested
-Norm ranges will vary btwn diff lab tech
-Pop used for testing may not be randomly distributed & skew ranges towards 1 en
-Some % of pop w/dx will have norm lab results


What is the lab cycle (from vein to brain)?

Pre-analytic Phase: decide to order test, place order, lab gets it, ID info entered, specimen collected (errors 62%)

Analytic Phase: specimen analyzed

Post-analytic Phase: report generated, result given to dr, data interpreted, clinical response to result (errors 23%)


What are sources for invalid lab results?

Pre-ana 62%:
Pt ID & prep, Phlebotomy site & prep, test collection procedures (tech, order of draw, proper tube mixing, correct volume), specimen handling/processing, transport

Post-ana 23%:
Incorrect data entry, oral miscommunication of results, error of reporting EMR, provider fails to retrieve results, failure to communicate critical values, provider misinterprets results

Least in ana phase


What questions should be asked before ordering tests?

Why is test being ordered?
What are the consequences of not ordering the test?
How good is the test in discriminating btwn dx?
How are the test results interpreted?
How will the test results influence pt management & outcome?*****