1. Introduction and chemical pathology lab Flashcards
what happens when someone has an infection?
- causes of fever and lymphadenopathy can be considered (e.g. viral illness, glandular fever)
- causes of diarrhoea can be considered (virus, bacteria, parasites)
- tests can be requested: FBC, ESR (erythrocyte sedimentation rate), CRP, liver function tests, urea and electrolytes, blood glucose, stool culture
what are the 3 tests done in chemical pathology?
- liver function test: albumin, total bilirubin, alkaline phosphatase, alanine amino-transferase
- urea and electrolytes: sodium, potassium, urea, creatine
- blood glucose
what do the colours on different blood tubes mean?
RED TOP: nothing inside - blood will clot within 5mins
YELLOW TOP: gel to speed up clotting - helpful to separate serum and RBCs
PURPLE TOP: potassium EDTA - anticoagulant that preserves red cells for 6hrs
GREY TOP: fluoride oxalate (poison) - kills red cells for blood glucose measurement
in what coloured tops is blood for different tests placed?
urea & electrolytes - yellow/red
glucose - grey to stop glycolysis
HBA1c - purple (measuring blood glucose over 3months)
thyroid FT - yellow/red (blood clots so you can measure TSH and T3/T4)
liver function tests - yellow/red
what is HBA1c?
a substance measured in diabetes - HBA1c is a band in electrophoresis that slows down because glucose makes the molecule bigger. glycation takes 3 months so we can see if a diabetic patient has been monitoring their blood glucose properly
what’s the difference between serum and plasma?
serum: no clotting factors
plasma: clotting factors
this is why clotting allows the serum (yellow liquid) to be tested
what is an anticoagulant?
anticoagulants such as EDTA and heparin result in clotting factors being unused
blood can be separated into red cells and plasma during centrifugation so that electrolyte levels can be measured from the plasma
what does a green top tube contain?
heparin
what does a blue top tube contain and what is it used for?
citrate (anticoagulant that works by removing calcium)
- used to measure clotting factors (e.g. if the liver isn’t working the patient cannot make clotting factors)
- the tube is filled to the top, a sample is removed and calcium is added. the time taken to clot is recorded
- prothrombin time (PT) and partial thromboplastin time (PTTK) can be measured
how is blood glucose measured?
- red cells consume glucose (anaerobic glycolysis)
- fluoride oxalate prevents red cells from using glucose so glucose levels stabilise and blood glucose can be obtained
when do you contact the chemical pathologist?
- when you want a sample to be rapidly centrifuged out of hours
- when you want to measure hormones that change quickly such as insulin (breaks down quickly)
- when you urgently need CSF glucose and proteins to be measured (e.g. meningitis)
why do samples of blood have high potassium?
when blood is taken 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 and red cells are full of potassium
what happens to creatine and urea during renal failure?
both rise
why is creatine used to assess renal function?
it is a marker of glomerular filtration rate. very little is absorbed or secreted by the tubules
why is urea used to assess renal function?
urea levels rise when a patient is dehydrated but GFR stays the same to the end
