Clinical Chemistry Flashcards
What is it for?
Biochemical methods are applied to the study of disease - usually confined to studies on blood, urine and other body fluids because of ease in obtaining such specimens
What is the use?
Diagnosis: Confirmation of rejection of clinical diagnosis
Treatment / monitoring: Monitoring the course of illness and / or response to treatment
Prognosis: Information regarding outcome of disease
Screenin: detection of subclinical disease
What are common specimens?
Blood, serum or plasma, Urine, Cerebrospinal fluid - however CSF is not easy to obtain
How is whole blood separated
From top to bottom
Plasma - anticoagulant present - contains fibrogen ]
Serum - no anticoagulant
Clot - formed encapsulating cells
Red tubes….
Have no anticoagulant / perservatives
Collects serums
20-30 mins required to allow blood to clot before centrifuging
Grey tubes….
Plasma or whole blood where glycolytic inhibition is required. Prevent blood cells from using glucose
Contains sodium fluoride and potassium oxalate - stablises glucose in plasma
Green tubes …
Contains either sodium or lithium salt of haparin - inhibiting thrombin so blood does not clot - separates plasma
Lavender tubes…
Contain EDTA - chelates calcium and inhibits coagulation
Not suitable for measuring K+
Preanalytical errors
Most errors
wrong specimen,
outside - mislabelling, incorrect perservation
inside (small percent) - sample log-in, centrifugation, dilutions, aliquoting, pipetting, sorting of specimens
What is pre-analytical?
Test requesting
Patient preparation
Timing of collection
Patient identification
Collection process
Sample transportation
Sample handling / storage
Collection error - stasis during venipuncture
long tourniquet placement (the strap on arm)
This will cause:
- Blocked flow and increased pressure
- Blood input continues
- Water and small molecules escape
- Big molecules increase in conc.
- Plasma components are falsely elevated
- use of tourniquet for over 1-3 mins causes elevation in albumin, cholestrol and haemoglobin
Collection error - blood sampling technique
Haemolysis -> release of rbc contents, rupture of erythrocyte cell membranes causing release on intracellular contents. Most common from ED.
Leakage of RBCS - produces false high K+, Pi and LDH.
Easily occurred when blood is drawn rapidly with force
Collection error - Wrong tube
Eg. K2-EDTA for K+ or Ca.
Different tubes contain different substances made for different purpose
Collection error - Sample contamination
Patient - drip arm: drip installed peripherally
Tube - sample being poured from one tube to another or contamination during wrong order draw
Order of draw to prevent contamination
1, Blood ciultures
First in order of draw to prevent needle contamination is made with stoppers from other tubes, which are not sterile. A second set of blood cultures requires a separate collection
2, Citrate (Blue)
Second in order of draw to prevent carryover of anticoagulant from other tubes that could alter the results of coagulation studies
3, Serum (red)
Third in the order of draw to prevent anticoagulants known to affect potassium and other chemistry results from carrying over into this tube
4, Heparin (green)
Fourth in the order of draw to prevent anticoagulants known to affect potassium and other chemistry results from carrying over into this tube
5, EDTA (lavender)
Fifth in the order of draw so that this potassium-rich anticoagulant doesn’t carry over into other tubes that are tested for analytes adversely affected by this addictive (eg potassium, calcium)
6, Glycolytic inhibitor (grey)
(e.g. Oxalate, sodium fluoride, etc)
Last in the order of draw to prevent the impact this anticoagulant has on RBC morphology, potassium levels, coagulation studies and other analytes
