Laboratory Diagnostic Methods Flashcards
Why is it important to only do the necessary tests?
- many tests are expensive and this is a cost to the NHS
What are rashes a sign of?
Allergies
Infection (specific ones e.g. shingles)
FBC
Full Blood Count
ESR
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)
CRP
C reactive protein (marker or inflammation)
LFTs
Liver Function tests
U&E
Urea and Electrolytes
What is important when filling out a blood sample form?
- 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
Which tube is used for U&E?
Serum in yellow/red top
What anticoagulants are inside the different blood tubes?
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
Which tube is used for Glucose?
Glucose: plasma in grey top
Which tube is used for HbA1c?
Plasma in purple top
Which tube is used for TFT?
Serum in yellow / red top
Which test tube is used for LFT?
Yellow / Red top
What is the difference between Serum and Plasma?
Plasma has clotting factors. Plasma does not have clotting factors.
Why is it important to have a blood sample checking for insulin done fast?
- Insulin is very labile
- you cannot wait an hour
HbA1c
- long term indicator of glucose levels
How do things seperate in the yellow tube?
- Hb is heavy and goes to the bottom
- gel intermediate
- serum is light and stays in the top
When would you use no anticoagulant? What happens?
- U&E : serum in yellow/red top
- Blood clots, using up all clotting factors
- Clot can be removed, leaving serum
What happens in a tube with anticoagulant?
- EDTA or heparin
- Clotting factors unused
- Blood can be separated into red cells and plasma
- plasma has clotting factors (serum does not)
What is in a tube with a blue top?
citrate (for measuring clotting factors)
Measuring glucose
- 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
What is measured in liver function testing?
- albumine
- ALP
- ALT (alanine transferase)
- TBil (Bilirubin)
What is important when sending a CSF sample to the lab?
- 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)
CSF sample - what are the results in bacterial meningitis?
- high protein
- low glucose
When do you need to contact a chemical pathologist?
- 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
What is a potential cause of high potassium by staff error?
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.
What is creatinine a marker of?
GFR
What does a normal creatinine and a high urea suggest?
dehydration
What to high urea and high creatinine suggest?
- kidneys not working properly
- renal failure
- kidney damage also causes an increase in creatinine
Liver enzymes
- 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…
What test would you order for a better look at the liver values?
- Liver
- gamma GT
- AST
What tests show the function of the liver?
- 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
Cardiac enzymes
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.
What are the specific cardiac enzymes that are tested for?
Troponins
Creatine kinase (CK)
Aspartate amino transferase (AST)
Lactate Dehydrogenase (LDH)
=> by the patterns you can tell when the MI occurred
