L2 Pre analytical errors

Question 1

What is the possible biological variable of creatinine?

Answer 1

• Creatinine is lower in the elderly (age)

- Creatinine is variable in different sexes (control: sex-specific reference intervals)

Question 2

Possible biological variable in pregnancy?

Answer 2

• increase in intravascular volume, hormonal changes
• albumin is lower due to dilution
  > pregnancy-specific reference interval

Question 3

List the possible cyclic variations.

and how to correct them

Answer 3

1. Diurnal variation
   - Concentration higher in the morning: ACTH, cortisol, iron
   (standardized collection time)
2. Pulsatile release
   - GH (multiple samplings > plot day curve/ dynamic function tests)
3. Menstrual cycle
   - estradiol, progesterone, LH, FSH, iron

Question 4

Why do we have to check lipid profile within 24 hour of AMI?

Answer 4

May give a false low result because total cholesterol falls after 24 hours

Question 5

What are the differences between FOB by guaiac-based test and by immunochemical method?

Answer 5

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

Question 6

Recent food intake (triglyceride intake) interferes with what lab test results?

Answer 6

• Cr, ALT

- may cause pseudohyponatremia (elevated triglyceride)

Question 7

Give an example of how recent drug intake interferes with lab results.

Answer 7

1. Thyroxine, iron intake

- solved by sample take before the dose, measure Fe by ferritin level

Question 8

How does exercise (increased muscle activity) interfere with lab result? (3)

Answer 8

• increase muscle content (CK, LDH, AST)

Question 9

How posture can affect lab result?

Answer 9

Standing

1. Blood pools in LL, increased protein and protein-bound substances in the blood
2. Decreased plasma volume > stimulate RAAS

Question 10

The collection time is important in drugs with therapeutic drug monitoring.
When is digoxin monitored?
When is lithium monitored?

Answer 10

Digoxin: at least 6 hour post-dose
Lithium: 12 hours post-dose for lithium

Question 11

What can be the possible effect of using a tourniquet?

Answer 11

• Application > 1 min will cause occlusion!

- > increase back presure > hemoconcentration > increase total protein, albumin and protein-bound analytes

Question 12

What are the differences between arterial and venous blood? ($)

Answer 12

Venous blood

• less PO2
• more PCO2
• more HCO3
• lower pH

Question 13

What is drip arm? (1)

List the 2 types of drips and their effects. (4)

Answer 13

Collection of blood distal to the infusion site

1. Normal saline
   - dilution of protein and protein-bound molecules
2. Dextrose water (D5)
   - dilution of Na (spurious hypoNa)
   - but an increase in blood glucose and K+!
3. D5 solution + KCl
   - pseudokyper K+ if KCl is added
   - dilution of Na

Question 14

What is the order of draw when using collecting tubes?

Answer 14

白 藍紅綠紫灰

> to prevent carryover od additives

Question 15

The white collection tube is for special clotted blood. Test for?

Answer 15

Trace metals

Question 16

The blue collection tube is the potassium/trisodium citrate tude, Test for?

Answer 16

Clotting profile

Question 17

The red (serum clot activator tube) or yellow (serum clot activator tube with gel separator) is for testing? (3)

Answer 17

1. Drugs
2. Tumor markers
3. Most hormones

Question 18

The green (heparin tube) is for testing? (6)

Answer 18

1. L/RFT
2. CaPO4
3. Urate
4. CK
5. LDH
6. GGT

Question 19

The EDTA (purple tube) is for collecting?

Answer 19

1. CBC

2. HbA1C

Question 20

They grey tube (Fluoride/oxalate - glycocytic inhibtor) is for collecting?

Answer 20

plasma glucose

Question 21

What will EDTA contamination cause - should not be used for RFT?

Answer 21

1. increased K+ (contamination)
2. reduced Ca2+ (chelation)
3. reduced ALP (chelation of Zn, Mg - essential cofactors for ALP activity)

Question 22

Heparinized syringe is for ABG and ionised calcium.

Heparin > ______% of total volume causes significant error in ________ and _________ (state the change too).

Answer 22

> 10%

• decrease in pH
• increase in PO2

(max 0.1ml 1000U heparin in 2ml sample)

Question 23

Blood sample is sent with _____________to the lab for immediate analysis of heparinized syringe to minimize enzyme activity.

Answer 23

ice bath

Question 24

How can air bubble interfere with lab results.

How to prevent it?

Answer 24

• increase in PO2
• decrease in PCO2
• Tap the syringe to remove the bubble

Question 25

What is the problem with in vitro hemolysis? (3)

Answer 25

1. Release of intracellular contents like K, LDH, AST 2. Dilution of plasma constituents 3. Red color of Hb will interfere with results of other test

Question 26

What are the 2 main problems in post-collection of blood?

Answer 26

1. Transportation time | 2. Transportation method

Question 27

What will happen to WBCs if there is prolonged transportation time?

Answer 27

1. metabolism continues (increase CO2, H+, lactate, reduced glucose, O2) 2. after O2 consumption -> release cellular content (K+, LDH, AST)

Question 28

What will happen to unstable analytes like ACTH, insulin, PTH if there is prolonged transportation time? General solution?

Answer 28

proteolysis of peptide hormones - ice-water bath

Question 29

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.

Answer 29

Hemolysis; | Warm sand, thermos

Question 30

The blood sample shows hyperkalemia. | Possible pre-analytical errors?

Answer 30

Pre-collection 1. Wrong patient 2. Underlying renal disease 3. Medications Collection 4. Hemolysis 5. Contamination - K3 EDTA Post collection 6. Prolonged storage

Question 31

The blood sample shows hyperkalemia together with Low Ca2+ and Mg. Most Possible pre-analytical error?

Answer 31

Likely K3 EDTA contamination