Pre-analytical errors

Question 1

For analytes, such as glucose and cholesterol, patients need to be __ for at least 12 hours prior to veni-puncture.

Answer 1

fasting (absence of food and liquids)

Question 2

For analytes, such as cortisol and adrenocorticotropin, have _ _, where the analyte is at its__ level in the morning, and the levels gradually ___ during the course of the day.

Answer 2

diurnal variations
highest
decrease

Question 3

Correct procedure when using a tourniquet. & consequence if not done correctly.

Answer 3

• 3-4 inches above venipuncture site
• used no longer than 2 min
• release tourniquet before withdrawing needle
x If 2+ min = inc. K+ bc haemolysis, inc lactic acid

Question 4

What happens if the alcohol @ the site of venipuncture is not completely dried?

Answer 4

Contaminate the sample = Haemolysis

Question 5

IN order which veins is best to collect blood from?

Answer 5

1. Median cubital vein
2. Cephalic vein
3. Basilic vein

Question 6

What can excessive probing do to the sample?

Answer 6

haemolysis = inc K+

Question 7

Phlebotomy order of draw (colour of top) [4]

Answer 7

1st: blood culture bottle/tube (Yellow / y-black)
2nd: coagulation tube (light blue)
3rd: non-additive tube (red) - just blood
4th: additive tubes

Question 8

Phlebotomy order of draw (colour of top) FOR ADDITIVES TUBES [5]

Answer 8

a) SST (red-grey / gold) - has gel separator & clot activator
b) Sodium heparin (dark green) -> collect plasma
c) PST (light green) - has Li heparin anti-coag. & gel separator -> collect plasma
d) EDTA (lavender)
e) Oxalate/fluoride (light grey) or other addatives

Question 9

What cases cause pseudohyperkalemia?

Answer 9

• Sample collected in K-EDTA
• Haemolysis by prolonged use of tourniquet, contamination from alcohol
• vigorously shaking the tubes
• respinning in centrifuge

Question 10

For collecting serums, you use BD SST tubes that contain _ _ and needs to be inverted _ times => _ under _ temperature for _ mins

Answer 10

clot activator
5x
specimen clot completely
room temp
30 min

Question 11

Which specimens are heat sensitive - kept chilled

Answer 11

• ACTH
• acetone
• ammonia
• FFA
• lactic acid
• pyruvate
• rennin

Question 12

Which specimens are photo-sensitive - kept dark

Answer 12

• bilirubin
• B-carotene
• erythrocyte protoporphyrin

Question 13

What’s the ideal procedure done to a sample after venipuncture?

Answer 13

1. centriguge w/in 2hrs & seperate serum
2. Serum is stable at:
   - Room temp for 8hrs
   - Fridge (2-4ºC) for 48hrs
   - Freexer (-20ºC) for >48hrs

Question 14

What are heterophilic Ab? & why may its presence be an issue?

Answer 14

human Ab - arise in response to heterophile Ag from exposure to certain animals or infection
=> lead to false pos results in lab

Question 15

What must be done with serum samples before tested?

Answer 15

• needs to be clot completely before centrifugation and processing
• red top tubes clot for 45-60 min
• BD SST clot for 30 min
• samples from patients taking HEPARIN (anti-coag) will require MORE TIME to clot

Question 16

What potenital pre-analytical errors may occur if K+, Na+, Ca+ were below normal?

Answer 16

• Clot formation

- Drip contamination: dilute salts