Interpretation of Lab Results

Question 1

What is the diagnostic cycle?

Answer 1

Health problem
History and Exam
Test request and blood
Analysis
Test results
Interpretation

Question 2

What do you need to consider when collecting blood?

Answer 2

Dietary Restrictions - fasting - glucose, cholesterol and triglycerides.

Timing - duirnal variation - cortisol, testosterone, Therapeutic drug monitoring (time form last dose), some things are unstable.

Affected by venous stasis

Posture

Question 3

what are the different collection additives and tubes used?

Answer 3

Clotted blood:
White - plain serum no gel
Brown - plain serum gel

Clot quickly
Orange - Lithium Heparin (anticoagulant)
Red -Potassium EDTA (anticoagulant) - normal blood count

Green - Tri-sodium citrate (anticoagulant) - used for clotting studies
Yellow - sodium flouride?potassium oxalate (anticoagulant) - can tell glucose

Question 4

what is the reference population?

Answer 4

A healthy populations meausurements. Consider age, gender ethnicity.

Plot a graph.

Question 5

How would you interpret under the graph?

Answer 5

The mean is the middle of the graph
One standard deviation above and below the mean shows 67% of people’s measurments
Two standard deiviations is 95%
Three standard deviations is 99%

Question 6

How many people fall in the reference range?

Answer 6

95%

Question 7

How many healthy people fall outside the reference range?

Answer 7

1 in 20

Question 8

Are some people who fall outside the reference range still healthy?

Answer 8

Yes

Question 9

What shows a skewed distribution?

Answer 9

TSH

Question 10

What would happen if you altered a skewed distripution reference range to a gaussian reference range?

Answer 10

Millions of more people would have to undergo tests and this would be expensive

Question 11

What are the guidling of sub-clinical hypothyroidism?

Answer 11

If TSH is above 10 then have thyroxine unless pregnant

Question 12

Why could the TSH guidlines be an issue?

Answer 12

Every lab measures TSH slightly differently so if you get your blood test in one lab you might not get thiroxin but you might if you go down the road

Question 13

what affects reference ranges?

Answer 13

Precision - How reproducable is this result?

Accuracy - How near to the true value is this result?

Question 14

what happens to the reference range when you have poor precision?

Answer 14

It widens

Question 15

What happens to the reference range when its inaccurate?

Answer 15

It moves the reference range

Question 16

Why wouldn’t you give a reference range and an example of this type of molecule?

Answer 16

When the normal population have results which are associated with the disease e.g Cholesterol as there is no safe level of this.

Question 17

What two things could cause a result to change?

Answer 17

Analytical variation

Biological variation (within a day or between a day)

Question 18

How can you tell what change in result is significant to the clinicians?

Answer 18

Take into consideration both analytical and biological variation. There are tables for this.

You normally just monitor people and see if they get worse or better

Question 19

Is there normally overlap between healthy and diseased populations?

Answer 19

Yes

Question 20

What are cut offs and clinical sensitivity and specificity?

Answer 20

This at what point you say someone is ill.

If you put the cut off at the end of the reference range then you will have an increase in false negative (poor clinical sensitivity) but good clinical specificity (few false positives).

If you put the cut of at the beginning of the disease range you will get poor specificity (many false posititives) and good sensitivity few false negatives).

Question 21

Screening tests - when deciding cut offs what do you need to know?

Answer 21

The prevalence of the disease in the populaiton

Question 22

What does prevalence mean?

Answer 22

Number of people in the population with the condition

Question 23

When doing a screen for a rare disease what do you need and why?

Answer 23

extremely high specificity and sensitivity as you are screening healthy people

Question 24

What are examples of rare diseases everyone is screened for?

Answer 24

Congenital hypothyroidism or PKU

Question 25

How many neonates tested for PKU and congenital hypothyroidism would be a false positive?

Answer 25

For every one neonate affected 25 would be a false positive

Question 26

What do you do if you are getting lots of false positives in screening?

Answer 26

change the cut off

Question 27

Errors in lab testing - Pre analytical - what is the common failures?

Answer 27

Choose correct tests in the correct manner on the correct patient

Question 28

what is a common disease people are diagnosed with because of error?

Answer 28

hyperkaelemia

Question 29

Analytical errors?

Answer 29

Is the test appropraite for clinical needs is there any interferance.

Question 30

What is a common interferance in immunoassays and how do you deal with this?

Answer 30

Endogenous antibodies and you can treat this to get rid of it.

Question 31

What happens in heterophilic antibody interferance?

Answer 31

In an immunoassay the heterophilic antibody binds onto the antibodies that are meant to be there stopping interactions.

Question 32

What happens to an immunoassay which is seeing High dose hook - false negative?

Answer 32

The antibodies are overwhelming the system and there is not enought labelling antibody leading to binding of analyte but no signal so it is not seen.

Question 33

What would happen is there was an incorrect result which said someone has high hCG?

Answer 33

Unnecessary chemo and hysterectomy

Question 34

What would happen is there was an incorrect result which said someone has low digoxin?

Answer 34

Overdose leading to toxicity

Question 35

What would happen is there was an incorrect result which said someone has low insulin?

Answer 35

confusion over diagnosis of insulinoma

Question 36

What would happen is there was an incorrect result which said someone has high troponin?

Answer 36

Incorrectly diagnosed MI

Question 37

Post analytical errors?

Answer 37

Communicating the right results

Getting the interpretation right