Chemical pathology

Question 1

what are examples of investigative tests?

Answer 1

• FBC= Full Blood Count
• ESR= Erythrocyte Sedimentation Rate
• CRP= C-reactive protein
• LFT (GP)= Liver Function Test
• U+E (GP) = Urea & Electrolytes (e.g. sodium, potassium)
• blood glucose (GP)
• stool culture

Question 2

red top

Answer 2

no anticoagulant

Question 3

what does the yellow top contain?

Answer 3

silica particles in gel

to speed up clotting

also contains a serum separator to split the blood cells and the plasma

Question 4

what does the purple top contain?

what is the purpose of this?

Answer 4

contains potassium EDTA

to stop blood clotting and therefore preserve the cells

Question 5

what does the grey top contain?
what does this do?
what can be analysed with grey top?

Answer 5

fluoride oxalate

poisons the RBCs to stop glycolysis so blood glucose can be measured (stop glucose usage)

Question 6

which tubes for U&E?

Answer 6

yellow or red

serum

Question 7

which tubes for glucose?

Answer 7

grey

plasma

Question 8

which tubes for HbA1c?

Answer 8

purple (preserve the RBCs with the glucose attached)

plasma

Question 9

why is HBA1c a good measure for blood glucose?

Answer 9

looks at glucose regulation over a longer period of time

RBC lifespan 120 days

patient may adjust glucose intake just before blood test

Question 10

which tubes for Thyroid Function Tests?

Answer 10

yellow or red

serum

Question 11

which tubes for LFT?

Answer 11

yellow or red

Question 12

why is serum collected?

Answer 12

there are no clotting factors present as blood has used them up

Question 13

how is serum extracted?

Answer 13

centrifugation with special gel producing a top layer of serum while the bottom contains all the clots

Question 14

what is contained in plasma?

Answer 14

serum and the clotting factors

Question 15

blue top

Answer 15

citrate anticoagulant

Question 16

what is the result of a poor aspiration technique on K+?

Answer 16

leads to RBC haemolysis which releases K+, confounding the potassium results

a pink sample is drawn and will need to be discarded
RBC has a high potassium content

Question 17

what are the main anticoagulants used?

Answer 17

EDTA and heparin

EDTA–> lavender, pink

Heparin–>green, navy blue

Question 18

what is the effect of using anticoagulants in the blood sampling?

Answer 18

clotting factors remain unused so the plasma can be separated from the RBCs with CFs still there

Question 19

what is used to measure CF levels?

Answer 19

blue top

reversible

Question 20

why is a grey top used for glucose measurement?

Answer 20

fluoride oxalate kills the RBCs so glucose in the blood is not used up

Question 21

when should you contact a chemical pathologist? [3]

Answer 21

• need for rapid centrifugation out of hours
• measuring labile hormones like insulin
• urgently need CSF glucose and protein measurements (meningitis rapidly consumes glucose)

Question 22

what does concentrated urine usually mean the patient is experiencing?

Answer 22

dehydration

Question 23

what will rise in renal disease?

Answer 23

urea and creatinine

Question 24

what is creatinine a measure of?

Answer 24

GFR (little absorbed or secreted)

Question 25

what happens to liver enzymes in liver disease?

Answer 25

lots of leakage into the blood

Question 26

what enzymes are usually measured in LFTs?

Answer 26

o ALT 
– Alanine Aminotransferase.
o AST 
– Aspartate Aminotransferase/Transaminase.
o ALP 
– Alkaline Phosphatase.
o GGT
– gamma-glutamyl transferase 

other:
o Albumin
o Bilirubin – TBil

Certain patterns of leakage will follow for different forms of liver damage.

Question 27

what may a high ALP indicate?

Answer 27

Post-fracture, ALP will rise as osteoblasts secrete ALP as they make new bone.

Question 28

what may a high Bilirubin indicate?

Answer 28

if this is up, then there may be something wrong with the biliary tree.

Question 29

what would be done for a suspected MI?

Answer 29

ECG then cardiac enzymes

o Troponins.
o Creatine kinase (CK).
o Aspartate amino transferase (AST).
o Lactate dehydrogenase (LDH

Question 30

which cardiac enzymes are measured?

Answer 30

o Troponins.
o Creatine kinase (CK).
o Aspartate amino transferase (AST).
o Lactate dehydrogenase (LDH).