L2 Pre analytical errors Flashcards
What is the possible biological variable of creatinine?
- Creatinine is lower in the elderly (age)
- Creatinine is variable in different sexes (control: sex-specific reference intervals)
Possible biological variable in pregnancy?
- increase in intravascular volume, hormonal changes
- albumin is lower due to dilution
> pregnancy-specific reference interval
List the possible cyclic variations.
and how to correct them
- Diurnal variation
- Concentration higher in the morning: ACTH, cortisol, iron
(standardized collection time) - Pulsatile release
- GH (multiple samplings > plot day curve/ dynamic function tests) - Menstrual cycle
- estradiol, progesterone, LH, FSH, iron
Why do we have to check lipid profile within 24 hour of AMI?
May give a false low result because total cholesterol falls after 24 hours
What are the differences between FOB by guaiac-based test and by immunochemical method?
Guiaiac- based test
- can be interfered by food, proper dietary restriction is needed
- plant peroxidases (e.g. raw turnips, horseradish/ heme from food like red meat > peroxide > give blue color)
Immunochemical method
- Hb —anti-globin Ab –> color change
- dietary restriction not required
Recent food intake (triglyceride intake) interferes with what lab test results?
- Cr, ALT
- may cause pseudohyponatremia (elevated triglyceride)
Give an example of how recent drug intake interferes with lab results.
- Thyroxine, iron intake
- solved by sample take before the dose, measure Fe by ferritin level
How does exercise (increased muscle activity) interfere with lab result? (3)
- increase muscle content (CK, LDH, AST)
How posture can affect lab result?
Standing
- Blood pools in LL, increased protein and protein-bound substances in the blood
- Decreased plasma volume > stimulate RAAS
The collection time is important in drugs with therapeutic drug monitoring.
When is digoxin monitored?
When is lithium monitored?
Digoxin: at least 6 hour post-dose
Lithium: 12 hours post-dose for lithium
What can be the possible effect of using a tourniquet?
- Application > 1 min will cause occlusion!
- > increase back presure > hemoconcentration > increase total protein, albumin and protein-bound analytes
What are the differences between arterial and venous blood? ($)
Venous blood
- less PO2
- more PCO2
- more HCO3
- lower pH
What is drip arm? (1)
List the 2 types of drips and their effects. (4)
Collection of blood distal to the infusion site
- Normal saline
- dilution of protein and protein-bound molecules - Dextrose water (D5)
- dilution of Na (spurious hypoNa)
- but an increase in blood glucose and K+! - D5 solution + KCl
- pseudokyper K+ if KCl is added
- dilution of Na
What is the order of draw when using collecting tubes?
白 藍紅綠紫灰
> to prevent carryover od additives
The white collection tube is for special clotted blood. Test for?
Trace metals
The blue collection tube is the potassium/trisodium citrate tude, Test for?
Clotting profile
The red (serum clot activator tube) or yellow (serum clot activator tube with gel separator) is for testing? (3)
- Drugs
- Tumor markers
- Most hormones
The green (heparin tube) is for testing? (6)
- L/RFT
- CaPO4
- Urate
- CK
- LDH
- GGT
The EDTA (purple tube) is for collecting?
- CBC
2. HbA1C
They grey tube (Fluoride/oxalate - glycocytic inhibtor) is for collecting?
plasma glucose
What will EDTA contamination cause - should not be used for RFT?
- increased K+ (contamination)
- reduced Ca2+ (chelation)
- reduced ALP (chelation of Zn, Mg - essential cofactors for ALP activity)
Heparinized syringe is for ABG and ionised calcium.
Heparin > ______% of total volume causes significant error in ________ and _________ (state the change too).
> 10%
- decrease in pH
- increase in PO2
(max 0.1ml 1000U heparin in 2ml sample)
Blood sample is sent with _____________to the lab for immediate analysis of heparinized syringe to minimize enzyme activity.
ice bath
How can air bubble interfere with lab results.
How to prevent it?
- increase in PO2
- decrease in PCO2
- Tap the syringe to remove the bubble
What is the problem with in vitro hemolysis? (3)
- Release of intracellular contents like K, LDH, AST
- Dilution of plasma constituents
- Red color of Hb will interfere with results of other test
What are the 2 main problems in post-collection of blood?
- Transportation time
2. Transportation method
What will happen to WBCs if there is prolonged transportation time?
- metabolism continues (increase CO2, H+, lactate, reduced glucose, O2)
- after O2 consumption -> release cellular content (K+, LDH, AST)
What will happen to unstable analytes like ACTH, insulin, PTH if there is prolonged transportation time?
General solution?
proteolysis of peptide hormones
- ice-water bath
Pneumatic tube can be used as a transport method, it is quick but may cause ___________ due to sharp turn in route.
__________ can be used for cryoglobulin, which coagulates under 37 degrees.
Hemolysis;
Warm sand, thermos
The blood sample shows hyperkalemia.
Possible pre-analytical errors?
Pre-collection
- Wrong patient
- Underlying renal disease
- Medications
Collection
- Hemolysis
- Contamination - K3 EDTA
Post collection
6. Prolonged storage
The blood sample shows hyperkalemia together with Low Ca2+ and Mg.
Most Possible pre-analytical error?
Likely K3 EDTA contamination
