Laboratory Diagnostic Methods

Question 1

Why is it important to only do the necessary tests?

Answer 1

• many tests are expensive and this is a cost to the NHS

Question 2

What are rashes a sign of?

Answer 2

Allergies

Infection (specific ones e.g. shingles)

Question 3

FBC

Answer 3

Full Blood Count

Question 4

ESR

Answer 4

Erythrocyte Sedimentation Rate
(if it is higher than usual it is a sign of infection, usually 1mm per hour, it is how much the erythrocytes fall in a timespan of 1h)

Question 5

CRP

Answer 5

C reactive protein (marker or inflammation)

Question 6

LFTs

Answer 6

Liver Function tests

Question 7

U&E

Answer 7

Urea and Electrolytes

Question 8

What is important when filling out a blood sample form?

Answer 8

• tick the tests you want
• double check the patients name (ask them what their name is, check their bracelet)
• make sure you use the correct tube!
• let the lab know if it is urgent

Question 9

Which tube is used for U&E?

Answer 9

Serum in yellow/red top

Question 10

What anticoagulants are inside the different blood tubes?

Answer 10

Red top - have none
Yellow top - have gel to speed up clot
Purple top - have potassium EDTA (keeps cells alive, measure Hb, RBCs, FBC but not for electrolytes due to K)
Grey top - have fluoride oxalate (poison) -> to top red cells from glycolysis and measure glucose levels

Question 11

Which tube is used for Glucose?

Answer 11

Glucose: plasma in grey top

Question 12

Which tube is used for HbA1c?

Answer 12

Plasma in purple top

Question 13

Which tube is used for TFT?

Answer 13

Serum in yellow / red top

Question 14

Which test tube is used for LFT?

Answer 14

Yellow / Red top

Question 15

What is the difference between Serum and Plasma?

Answer 15

Plasma has clotting factors. Plasma does not have clotting factors.

Question 16

Why is it important to have a blood sample checking for insulin done fast?

Answer 16

• Insulin is very labile

- you cannot wait an hour

Question 17

HbA1c

Answer 17

• long term indicator of glucose levels

Question 18

How do things seperate in the yellow tube?

Answer 18

• Hb is heavy and goes to the bottom
• gel intermediate
• serum is light and stays in the top

Question 19

When would you use no anticoagulant? What happens?

Answer 19

• U&E : serum in yellow/red top
• Blood clots, using up all clotting factors
• Clot can be removed, leaving serum

Question 20

What happens in a tube with anticoagulant?

Answer 20

• EDTA or heparin
• Clotting factors unused
• Blood can be separated into red cells and plasma
• plasma has clotting factors (serum does not)

Question 21

What is in a tube with a blue top?

Answer 21

citrate (for measuring clotting factors)

Question 22

Measuring glucose

Answer 22

• Red cells consume glucose (anaerobic glycolysis), so the longer this is left out, the lower the glucose may read
• Fluoride Oxalate (poison) prevents the red cells from using glucose

KNOW THIS

Question 23

What is measured in liver function testing?

Answer 23

• albumine
• ALP
• ALT (alanine transferase)
• TBil (Bilirubin)

Question 24

What is important when sending a CSF sample to the lab?

Answer 24

• make sure that they have time before you take the sample
• it should be analysed right away
• e.g. if you are suspecting meningitis you want to know the amount of glucose and protein in CSF (low glucose would indicate bugs in the CSF)

Question 25

CSF sample - what are the results in bacterial meningitis?

Answer 25

• high protein

- low glucose

Question 26

When do you need to contact a chemical pathologist?

Answer 26

• When you want the sample to be rapidly centrifuged out of hours
• When you want to measure labile hormones such as insulin
• When you urgently need CSF glucose and protein to be measured

Question 27

What is a potential cause of high potassium by staff error?

Answer 27

Haemolysis: if you aspirate very hard the blood cells will aspirate and the potassium might go up because blood was not taken well. Then the lab would generally say: potassium: heamolysed
You have to have a needle thick enough to avoid hameolysis.

Question 28

What is creatinine a marker of?

Answer 28

GFR

Question 29

What does a normal creatinine and a high urea suggest?

Answer 29

dehydration

Question 30

What to high urea and high creatinine suggest?

Answer 30

• kidneys not working properly
• renal failure
• kidney damage also causes an increase in creatinine

Question 31

Liver enzymes

Answer 31

• Are present in the liver
• A tiny amount normally leaks into the blood
• In liver disease, more of these enzymes leak into the blood
• With experience you can tell what liver disease a patient has from the pattern of the leak…

Question 32

What test would you order for a better look at the liver values?

Answer 32

• Liver
• gamma GT
• AST

Question 33

What tests show the function of the liver?

Answer 33

• In addition to “Liver”, one would need to measure AST and GGT in a patient with jaundice
• “Liver” includes
  Albumin: synthesised in the liver
  Bilirubin
  Alkaline Phosphatase
  ALT (alanine amino-transferase)
• > if the liver fails you make less albumin
• > Hb is broken down to Bilirubin which is dark yellow or brown; liver problem: the faeces are pale and urin is brown
• > ALP shows that there is something wrong with bile
• > ALT is high in hepatitis

Question 34

Cardiac enzymes

Answer 34

Are present in the heart muscle
During a heart attack, heart muscle is damaged

These enzymes leak into the blood in large amounts
Thus we can tell you if someone has really had a heart attack

Diaebtic patients have neuropathy, they might not know that they have damage to the heart because they don’t feel the pain.

Question 35

What are the specific cardiac enzymes that are tested for?

Answer 35

Troponins
Creatine kinase (CK)
Aspartate amino transferase (AST)
Lactate Dehydrogenase (LDH)

=> by the patterns you can tell when the MI occurred