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Flashcards in Intro to Lab Medicine Deck (21):
1

What is a reference range?

Population mean +/- 2 std deviations

2

Total cholesterol

Good: Below 200
Bad: >240

3

HDL

Good: >60
Bad: <40

4

TG

Good: <150
Bad: >500

5

LDL

Good: <130
Bad: >160

6

Normal blod glucose/A1c

70-99
<5.7

7

Diabetes

>126
>6.5

8

Tells what fraction of people with disease have a positive test result

Diagnostic sensitivity

TP/ (TP+FN)

9

Tells what fraction of healthy people have a negative test

diagnostic specificty

TN/ (TN +FP)

10

Increasing sensitivity leads to _______ sensitivity

decreasing

11

What is a receiver operator curve?

 Plot of sensitivity vs. 1‐specificity

 Graphical representation of separation

 Measure area under the ROC curve (AUC)

 Higher values for AUC indicate better ability
to SEPARATE the groups of interest

12

If a patient has a positive test result, how liekly is he to have the disease?

PPV =
TP/ (TP+FP)

13

A patient's test result for a disease is positive. The test is 80% sensitive and 95% specific. How likely is it she has the disease?

TP=80, FP =5, so TP/(TP+FP) = 80/85 or 94%

14

If your patient has a negative test result, how likely is she to not have disease?

TN/(TN+FN)

15

How does prevalence influence predictive values? Higher prevalence? Lower prevalence?

 Disease prevalence in a population has a significant impact on predictive values

 Higher prevalence = fewer FP (more likely to have a TP or disease... AIDS in africa)

 Lower prevalence = fewer FN (More likely to have a true negative)

16

How does prevalence effect PPV?

as prevalence increases PPV increases

17

What are examples of high prevalence?

 HIV‐1 infection prevalence in many sub‐ Saharan countries is in the 20‐30% range of the entire population
 The prevalence of Alzheimer disease increases dramatically with age: 1.5% of people aged 60‐69 have the disease vs. ~40% of those aged ≥90
 Specialist’s practice vs. primary care

18

Newborn screening programs have a high FP which in turn affects PPV...

LOW PPV

19

What are examples of pre-analytical errors?

• Test selection and ordering
– Wrong test, order missed or mis‐transcribed
• Specimen collection
– Wrong type of specimen or container, wrong time
of collection, contamination, insufficient sample • Specimen labeling (identification)
– MOST COMMON
• Transportation to laboratory
– Delays and time‐dependent changes in constituents, loss of sample, hemolysis

20

What are analytical error examples?

 Clerical errors in the laboratory
 Sample identification mix‐ups
 Wrong test performed
 Technical errors (Assay failure, interferences)

21

 Results not communicated
 Results communicated to wrong physician  Wrong results communicated
 Results not interpreted correctly

Are examples of...

Post-Analytical error