Chemical Pathology Lab

Question 1

What anticoagulants are in the different tubes?

Answer 1

Red top – no anticoagulant

Yellow top – gel to speed up clotting

Purple top – potassium EDTA
- This stops the blood clotting and thus preserves the cells (keeps the cells alive).

Grey top – Fluoride oxalate
- This is a poison to RBCs and is used when you want to measure blood glucose – as if the cells were alive, they would consume glucose in the blood continuously

Question 2

What would you ask for from a stool/ urine sample?

Answer 2

Microscopy
Culture
Sensitivity

Question 3

What tube is used for different tests?

What’s the difference between serum and plasma?

Answer 3

U&E (urea and electrolytes) – serum in yellow/red top

Glucose – plasma in grey top

HBA1c – plasma in purple top
- Haemoglobin A1c – this is haemoglobin with glucose attached to it and is a measure of the glucose in the blood over a longer period (3 months).

TFT (thyroid function test) – serum in yellow/red top.

LFT (liver function test) – in yellow/red tops

• Serum = no clotting factors – when the blood used up all the clotting factors and clots are removed
• After being in a centrifuge with a special gel, the blood will separate and the top layer is the serum whilst the bottom layer is the clots

Plasma = serum + clotting factors

Question 4

What can falsely produce a high potassium result?

Answer 4

haemolysis - blood left out or multiple punctures to obtain sample

Question 5

What liver enzymes are measured in a LFT?

Answer 5

• A tiny number of liver enzymes normally leak into the blood but in liver disease, lots of these enzymes leak into the blood.
• • If you suspected jaundice, as well as testing liver enzymes, you would also test – AST and GGT levels.

Enzymes usually measured in liver tests are:
- ALT – Alanine Aminotransferase
- AST – Aspartate Aminotransferase/Transaminase
- ALP – Alkaline Phosphatase
> Post-fracture, ALP will rise as osteoblasts secrete ALP as they make new bone
- Albumin
- Bilirubin – TBil – if this is up, then there may be something wrong with the biliary tree
> Certain patterns of leakage will follow for different forms of liver damage

Question 6

Which cardiac enzymes leak into the blood post MI?

Answer 6

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