Clinical Biochem 1

Question 1

Differentiate between invasive and non-invasive tests? risk?

Answer 1

Invasive
- examines fluid or tissue by using a needle, tube, device or scope to penetrate skin/enter body
- pose some risk to patients

Non-invasive
- does not require skin penetration or an instrument entering the body
- minimal risk

Question 2

Differentiate between accuracy & precision

Answer 2

Accuracy
- mean measure is close to the true value (not always close with each other)

Precision
- Agreement of results when test is run many times on the same sample
- Not always accurate or close to mean value

Question 3

Define sensitivity
What does a high sensitivity indicate? Calc?

Answer 3

• identify positive results in patients WITH the disease
• true positive rate % with patients who actually test positive

Goal: Low rate of false negatives
- TP / (TP + FN) x 100

Question 4

What is sensitivity tests good for?

Answer 4

SNOUT

• NEGATIVE result is good for ruling OUT

Question 5

Define specificity. What does a high specificity indicate? Calc?

Answer 5

• identify negative results in patients who DO NOT have the disease

Goal: have low rate of false positives

TN / (TN + FP) x 100

Question 6

What are specificity rests good for?

Answer 6

SPIN

• Positive result is good for ruling in

Question 7

Define sensitivity of an assay

Answer 7

Range at which an assay can accurately measure an analyte

Question 8

Define specificity of an assay

Answer 8

Degree of cross-reactivity of the analyte with other substances

Question 9

What does a positive predictive value indicate?
What does a negative value indicate?

disease/no disease

Answer 9

+ predictive value = % of positive tests that are actually + (PRESENCE OF DISEASE)

• predicative value = % of negative tests that are actually - (ABSENCE OF DISEASE)

Question 10

Which values are dependant on prevalence of disease? which values are not

Answer 10

Dependent = predictive value

Not dependent = Sensitivity, Specificity

Question 11

Define reference range

Answer 11

A set of previously defined values for some measurement used to interpret a lab test result

Question 12

What is gaussian normal distribution indicate about reference range and SD

Answer 12

• reference range can be 2 SD above/below the mean value

Question 13

What effect does increasing reference range have on sensitivity?

Answer 13

Decrease sensitivity

Question 14

Differentiate between quantitative and qualitative tests

Answer 14

Quantitative:
- Exact numerical measurement as an output

Qualitative:
- report an outcome as positive or negative without indication of the degree of positivity or negativity

Question 15

What factors should you consider in age?

Answer 15

Children: physiological immaturity (predictable)
Elderly: physiological changes (less predictable)

Question 16

What factors should you consider in pregnancy?

Answer 16

Troponin used to screen for blood clots
(it is increased during pregnancy, not accurate way to measure)

Question 17

What does hemoconcentration vs hemodilution mean

Answer 17

hemoconcentration: little fluid

hemodilution: fluid overload

Question 18

Explain methodological interference

Answer 18

drug interferes with analyte of interest

Question 19

Explain drug induced organ damage

Answer 19

drug can induce renal dysfunction

Question 20

Explain direct pharmacological effects

Answer 20

antibiotics inhibit bacterial growth in urine/blood

Question 21

What is the practical framework for interpretation and management of abnormal values (6)

Answer 21

1. How abnormal is the lab value compared to reference range
   - farther away = abnormal
2. Consider patient specific factors
   - some factors can explain abnormal values
   - some tests have different ranges for different factors (age, gender)
3. asses value to baseline value (assess rate of change)
   - Faster rate of change = clinical risk
   - intrapatient changes is expected?
4. assess value to baseline value (see potential trends)
   - continued trend up or down may be clinically important
   - small fluctuations are expected
5. Is the abnormality clinical significant
6. Does it require management