Chemical lab Flashcards
Why does fever occur?
We get a fever when we have an infection – it is a natural response due to cytokine signalling
If your temperature goes up, you feel awful, but this gives you a survival advantage (evolutionary)
Nowadays we have we have antibiotics, so fever is not as advantageous and we try to temper it
Increased temperature results in an increase in metabolism → speeds up the immune response
This makes a patient feel cold, so they try to warm up and this helps increase their body temperature
What tests can be used to try and find the cause of fever or diarrhoea?
o Full blood count, ESR, C-reactive protein
o Liver function tests
o Urea and electrolytes (assess renal function)
o Blood glucose
o Investigate possible viral illnesses
o Look at the stool culture (bacteriology)
Which are the main chemical pathology tests?
Liver function test: albumin, total bilirubin, alkaline phosphatase (ALP), alanine amino-transferase (ALT)
Urea and electrolytes: sodium, potassium, urea and creatinine
Blood glucose
How is blood taken?
BLOOD CAN BE TAKEN BY A GP, PRACTICE NURSE, JUNIOR DOCTOR OR MEDICAL STUDENT
If you collect blood, it needs to be collected into the right tube
If the tube is not right, the sample has to be thrown away
Make sure you confirm the patients name before, and label the tube with the patient’s detail
If it is urgent, ensure that the sample gets to the lab in time
What do the different top colours of blood bottles mean?
RED TOP: has nothing in it – blood will clot within 5 minutes
YELLOW TOP: contains gel to speed up clotting – helpful to separate serum and red cells
PURPLE TOP: contains potassium EDTA (anticoagulant, preserves red cells for 6 hours – haematology)
GREY TOP: contain fluoride oxalate (poison) – kill red cells – blood glucose measurement
Less common
GREEN TOP: contains heparin
• BLUE TOP: contains citrate (anticoagulant, works by removing the calcium → not clotting)
Which standard test tend to be done in each blood bottle?
U&E: serum in yellow/red top
Glucose: plasma in grey top – stops glycolysis
HBA1c: plasma in purple top – the more HBA1c you have, the worse the diabetes
Thyroid FT: serum in yellow/red top – blood clots, you can measure TSH and T3/T4
Liver function tests: in yellow/red top
PT/PTT: Blue top, add calcium cell how long clotting takes.
How is HBA1c test performed and interpreted?
This is measured in diabetes. Haemoglobin is glycated so glucose sticks to it. If you perform electrophoresis on red cells, there is a band of haemoglobin called HbA (normal). In diabetes, the HbA band is blurred, because
glucose sticks to the haemoglobin randomly (the more glucose, the more sticks, and the broader the band). TheHbA1c band is another band that slows down, because glucose makes the molecule bigger (moves slowly). Glycation takes 3 months – so we can see if a diabetic patient has been monitoring their blood glucose properly
What is the difference between serum and plasma?
Serum: no clotting factors
Plasma: Clotting factors (Electrolytes measured in plasma)
(If you dont add anticoagulant you can mix the blood to clot the plasma, removing the clot leaves only the serum and red cell layers.)
NOTE: RED CELLS MUST BE REMOVED FOR MOST ANALYSIS
How are glucose levels in blood measured?
Red cells consume glucose (anaerobic glycolysis)
The longer this is left out, the lower the glucose may read
Fluoride Oxalate (poison) prevents the red cells from using glucose – so we can get a blood glucose
Fluoride oxalate poisons the red cells, so glucose levels stabilise (otherwise red cells consume glucose)
When do you contact the chemical pathologist?
When you want the sample to be rapidly centrifuged out of hours
When you want to measure labile hormones such as insulin (breaks down quickly)
When you urgently need CSF glucose and protein to be measured (e.g. in meningitis – emergency)
Why may potassium be raised in a healthy blood sample?
When you take blood from a difficult vein, and the needle is small, red cells are damaged as they squeeze
through the needle into the syringe. This results in haemolysis. Red cells are full of potassium, so this results in high potassium in the sample collected.
How is renal function tested by chemical pathologists?
Creatinine is a marker of glomerular filtration rate. If it is normal, then the GFR is normal. Very little is absorbed or secreted by the tubules.
Urea levels rise when a patient is dehydrated but GFR stays the same to the end.
When you see the pattern of raised urea and normal creatinine, it often marks DEHYDRATION
In renal failure, the concentration of urea AND creatinine rise.
How is liver function tested by a chemical pathologist?
A tiny amount of liver enzymes normally leak into the blood. In liver disease, more of these enzymes leak into the blood (e.g. ALT)
Pattern of leak can be predictor for specific disease
Viral hepatitis - very high ALT (alanine amino-transferase)
Obstruction - very high ALP (Alkaline Phosphatase)
Also need to measure AST and gamma-GT in a patient with jaundice
Albumin: synthesised in the liver (low albumin suggests that the liver is not working well)
Bilirubin – you can tell if someone has high bilirubin, because they’ll have jaundice
How are cardiac enzymes used in diagnosis?
Done AFTER ECG
During a heart attack, heart muscle is damaged and cardiac enzymes leak into the blood in large amounts. So presence in blood indicates MI
What are the cardiac enzymes?
- Troponins – if this is high, there is definitely something wrong with the heart
- Creatine kinase (CK)
- Aspartate amino transferase (AST) – also in the liver
- Lactate Dehydrogenase (LDH) – also in the liver
