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Bench to bedside and beyond > 15. Clinical Biochemistry > Flashcards

15. Clinical Biochemistry Flashcards

1
Q

Why do we do biochemical tests?

A
  1. Diagnosis
  2. Monitoring
  3. Screening
  4. Prognosis
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2
Q

Why do we do biochemical tests? - Diagnosis

A
  1. Diabetes- check glycosylation of haemoglobin which is more accurate then the glucose test.
  2. thyroid dysfunction
  3. renal failure
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3
Q

Why do we do biochemical tests? - monitoring

A
  1. Drugs and therapies - testing they are working and are at high enough levels.
  2. Diabetes
  3. Complications - toxic effects of drugs
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4
Q

Why do we do biochemical tests? - screening

A
  1. heel pick test for babies - test the blood on card
  2. bowel cancer FIT tests
  3. cholesterol levels
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5
Q

Why do we do biochemical tests? - prognosis

A
  1. Progression of disease - renal disease
  2. cholesterol
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6
Q

How is most biochem testing done?

A
  1. mostly automated by very big machines
  2. testing whole blood or serum
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7
Q

What is the process of testing a medical sample?

A
  1. The test is requested by a doctor.
  2. Sample taken and delivered to the lab.
  3. Prepared for analysis by centrifuging to get rid of RBC.
  4. Put in the analysing machine
  5. If it is outside the normal range further testing is needed or pushed to the doctor for analysis
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8
Q

How do we know test results are correct?

A
  1. Most machines have internal quality control to check the machine is working
  2. More specialist test have external quality control
  3. compare against standards
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9
Q

What factors can effect test results?

A
  1. Pre-test: is it the right patient?
  2. Test: variability, interperson, interlab, carryover, contaminants.
  3. Post-test: results delivered to the wrong patient
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10
Q

Why do test results have variability?

A

Due to people being different.
Due to using different machines.

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11
Q

What is carry-over?

A

Another patients sample effecting a results.
Machines need to be cleaned properly between tests to ensure results are correct.
Use repeats.

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12
Q

What Pre-test factors effect test results?

A
  1. Time of day or is the patient fasted
  2. is the correct tube being used?
  3. is the correct specimen being used?
  4. Is it the correct patient?
  5. Has the sample been sent to the lab in a timely manner?
  6. Is the sample undamaged and uncontaminated?
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13
Q

What can damage blood samples?

A

Thin needles can burst the blood cells effecting results

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14
Q

Why is it important for the sample to be sent to the lab quickly?

A

Due to potassium leakage out of the cells down their concentration gradient. This can dramatically effect results.

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15
Q

What is in the yellow-topped blood tubes?

A

It is a serum separator tube. To separate out the RBC from the blood so we can test the serum.

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16
Q

What is in the grey-topped blood tubes?

A

Fluoride oxalate to stop the blood cells using glucose to give more accurate test results.

17
Q

What is in the pink-topped blood tubes?

A

An anticoagulant called EDTA. These are mainly for haematology tests

18
Q

What happens if the wrong blood tube is used?

A
  1. it could damage the cells
  2. it could affect the test results
19
Q

How does EDTA work as an anticoagulant?

A
  1. It using the metal ion K+ to form a complex.
  2. Ca2+ is in blood and as it is a smaller ion and more electropositive it displaces the K+.
  3. This is a good anticoagulant.
  4. But this blood sample couldn’t be used for measuring potassium levels.
20
Q

What is a reference range?

A

A 95% confidence interval that contains most of the normal levels for 95% of the population.
The 5% of people not within the confidence interval can still normal.

21
Q

Why do the samples need to be spun down?

A

To prevent potassium leaking from the cells into the serum.

22
Q

How can we detect whether the potassium in the samples is due to a disease/condition or due to leakage?

A

Both potassium and phosphate levels are higher within cells.
If the potassium is elevated due to leakage you would expect to see higher phosphate levels as well.

23
Q

What methods are most used in biochemistry testing?

A
  1. Photometric tests account for most standard testing.
  2. Ion-selective electrodes
  3. electrophoresis
  4. GC-MS
24
Q

What is photometric testing used for?

A
  1. Most standard assays
  2. Looking for a colour change. Usually an indirect one due to a series of reactions.
  3. NAD+ -> NADH
  4. lots of environmental stuff can interfere.
25
Q

What are ion-selective electrodes used for?

A
  1. testing for ion levels.
  2. Na+, K+, H+
  3. generation of a potential difference across a selectively permeable membrane.
26
Q

What is electrophoresis used for?

A
  1. separating compounds via chromatography
  2. comparison to controls
  3. can be used by itself or with other detection techniques
27
Q

What is GC-MS testing used for?

A
  1. Drug testing - both monitoring and illicit drugs
  2. Doping testing for athletes.
  3. Allows measurements at low concentrations.
  4. Break up into molecules and detect them.
28
Q

What do clinical chemists do?

A
  1. Work with the machines and do the testing.
  2. Discuss results with medical staff and discuss next steps.
  3. Recommended if other follow up tests are needed.
  4. Develop new methods of testing or improve current tests.
  5. Interpretation of more complex analysis
  6. Work with chemical pathologists and other lab staff.

Bench to bedside and beyond (20 decks)

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