Introduction and chemical pathology lab Flashcards
What is a likely cause of fever, rash and lymphadenopathy
Viral infection (e.g glandular fever) Causes prominent swelling of lymph nodes in the neck- to prevent infection becoming systemic.
If the patient has been travelling and presents with diarrhoea, what is the likely cause
Infectious
Virus, bacteria, parasites
State the different tests that the GP could perform regarding this case
FBC, ESR, CRP (haematology) LFTs U&Es Blood Glucose Ix of viral illness (virology) Stool culture - Bacteriology
Which 3 tests will be carried out by the chemical pathology department
LFTs
U and Es
Blood glucose
Describe the ESR
Erythrocyte Sedimentation Rate – the rate at which red blood cells settle out of suspension in blood plasma, measured under standard conditions
ESR increases in infection (due to presence of proteins and inflammatory cells in the blood).
Summarise the LFTs
Liver enzymes will be released upon insult to the liver (biliary blockage or viral hepatitis)
Biliary blockage- increased alkaline phosphatase with decreased Aspartate Aminotransferase/Transaminase.
describe CRP
Released from the liver during infection
acute phase protein.
What will be measured in the U&E test
Na/K/Urea/Creatinine
What will be measured in LFTs
Albumin
Total BR
o ALT – Alanine Aminotransferase.
o ALP – Alkaline Phosphatase.
Can also measure CRP, o AST – Aspartate Aminotransferase/Transaminase. and gammaGT alongside these
Why does the GP want to know these test results
Because he wants to make a diagnosis and, from the history and examination, thinks that these might either
give him a clue, or
the diagnosis
Who will take the blood
GP
Practice Nurse
Junior doctor
Medical student visiting the practice?
What is important to remember when you are collecting the blood
Which tube should you use?- use guidance- different labs use different anti-coagulants, if you use the wrong tube- you won’t get any results- waste of time and money.
If you get it wrong, the sample will have to be thrown away
Make SURE you get the correct patient
Describe the important logistics to consider when taking blood
LABEL the tube with the patient’s details
If it is urgent, ensure the sample gets to the lab in time
Describe the features of the different coloured tubes
o Red top – no anticoagulant (leave serum at the top)
o Yellow top – gel to speed up clotting.
o Purple top – potassium EDTA (can’t use for electrolytes- will give false results for K
§ This stops the blood clotting and thus preserves the cells (keeps the cells alive).
o Grey top – Fluoride oxalate- often used for glucose- preserves glucose in sample- can’t be used in glycolysis.
§ 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.
Describe the different tests which use the different coloured tubes
U&E : serum in yellow/red top Glucose: plasma in grey top HBA1c: plasma in purple top TFT: serum in yellow/red top Liver function tests: in yellow/red top
What is the difference between serum and plasma
U&E : serum in yellow/red top
Blood clots, using up all clotting factors
Clot can be removed, leaving serum
So if you put blood in tube and allow it to clot- clotting factors will sink to the bottom to form the clot- leaving a clot-free serum at the top- which you can centrifuge out for analysis.
Outline how the yellow tube works
Gel separates the blood from the serum upon centrifugation
Blood at the bottom (Hb is heavy)
Serum above gel
Potassium in blood cells- so it’s good for accuracy that the gel prevents mixing with the blood- you want to measure potassium in the serum.
Essentially, what will happen when you add any anticoagulant to the cells
EDTA or heparin
Clotting factors unused
Blood can be separated into red cells and plasma
Describe what will happen when you centrifuge blood with any anti-coagulant
Blood and neutrophils- bottom Gell barrier above this Density gradient fluid above this Lymphocyte and monocyte band plasma
What is found in the green top
Lithium
What is found in the blue top
Contains citrate
It is reversible and used to measure clotting factors
Citrate binds to calcium and prevents clotting
When you get a sample of blood in a citrate bottle, you add just the right amount of calcium to trigger the clotting cascade
Used to measure PT and APTT.
What is serum and what is it used to measure
When blood clots and you remove the clot you are left with serum
Serum contains electrolytes but NO clotting factors
How is gel designed so that it separates serum from the rest of the blood
It is more dense than serum but less dense than cells so it separates the serum from the cells
Outline how we measure blood 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
Summarise the role of chemical pathologists
Are in charge of the Chem Path laboratories
Also do research into better methods of getting results
Also do metabolic medicine clinics (diabetic clinics)
Do some tests…
What happens to the sample once the lab receive it
Chemistry is carried out on the serum or plasma
Thus, the red cells need to be separated off by centrifugation
Then, measure the concentration of…
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 (insulin will be destroyed by clotting- need lab to be ready)
When you urgently need CSF glucose and protein to be measured (high protein, low glucose- bacteria meningitis0 urgent diagnosis)
How will results be received
Are available on computer
If urgent are phoned to the requesting clinician
How is the “reference range” determined? (normal range not used- what is abnormal for one patient may be normal for another).
Interpretation of the results…
What is a common cause of low sodium and high potassium
Adrenal failure* (loss of aldosterone)
What else could cause a high potassium
Incorrect venipuncture
Sharp needle for small, feeble veins- aspirated too forcefully or into a larger vacuum- the blood cells will haemolyse- releasing K- skewing the results.
Will see rose instead of yellow serum due to release of Hb
Where are urea and creatinine produced
by muscle mass
Describe the difference between creatinine and urea
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.
In renal failure, the concentration of urea* and creatinine* rise
If creatinine is normal, but urea high, what is the likely cause
Acute dehydration
Kidney filtration fine- as GFR normal
But reabsorption is altered to preserve water and salt- so urea concentration in the urine rises.
GFR will eventually decrease, or will decrease in diabetic patient.
o Note that Addison’s disease also presents like this.
Where are the liver enzymes normally found
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 do LFTs include
Albumin: synthesised in the liver- so if low- liver failure
Bilirubin- liver breaks down Hb in dead red cells to make BR- sent to gallbladder to be excreted in G.I tract- BR makes faces dark.
Alkaline Phosphatase- high if biliary tract blocked- gallstones or tumour of the head of the pancreas.
ALT (alanine amino-transferase)- high in viral hepatitis.
The patient shows high BR (jaundice), low albumin and high AST and ALT, what is the likely diagnosis
Viral hepatitis.
Outline how we make a diagnosis
Ask the patient what is wrong
Take history: 26-year-old who has been to Thailand
Examine the patient
Do some tests…
Make a plan:
the plan should include doing some investigations…
When can cardiac enzymes be detected in the blood
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
Don’t just go off chest pain- it a patient has diabetic neuropathy- they may not feel the pain.
State the cardiac enzymes
Troponins
Creatine kinase (CK)
Aspartate amino transferase (AST)
Lactate Dehydrogenase (LDH)
Do an ECG- these are quicker than measuring enzymes
Where else is ALP found
Osteoblasts
§ Post-fracture, ALP will rise as osteoblasts secrete ALP as they make new bone.
What else could cause cardiac symptoms
A bleeding peptic ulcer
Why can patients with autoimmune disease get fever in the absence of an infection
Fever is caused by the immune system rather than the organism
Hence it can occur in autoimmune disease in the absence of an organism
