Preanalytical Factors

Question 1

Blood tube order of draw for CAPILLARY sample

Answer 1

“Every happy fish sings”
EDTA
Heparin
FlOx
SST

Question 2

Order of draw, venous blood

Answer 2

“Cultured cats stay happy eating fish”
Blood culture
Citrate
SST
Heparin
EDTA
FlOx
~~~

Question 3

Why is correct mixing of blood tubes important?

Answer 3

To ensure blood does not clot in anticoagulated tubes

Question 4

In what situations might skin puncture be appropriate?

Answer 4

1. Limited sample volume (eg paeds)
2. Repeated venipuncture has damaged veins
3. Limited access to veins due to eg burns/bandages

Question 5

Why is the order of draw different for capillary and venous samples?

Answer 5

The primary concerns for each sample are different. For capillary collection, cross-contamination is unlikely, but premature clotting is a risk. Therefore, tubes with anticoagulants have to be prioritised and serum tubes come last.

Question 6

What is serum?

Answer 6

The part of the blood remaining after coagulation has occurred and cells have been removed.

Question 7

What is plasma?

Answer 7

The noncellular component of anticoagulated whole blood

Question 8

What additives if any may be found in a blood tube?

Answer 8

No additive
Anticoagulants
Clot activator (silicone coating/silica particles)
Separator gel
Protease inhibitors

Question 9

How does using a plasma tube instead of a serum tube decrease turnaround time?

Answer 9

The specimen does not have to be left to clot before being tested

Question 10

List the anticoagulants found in tubes

Answer 10

Heparin
Ethylenediaminetetraacetic acid (EDTA)
Sodium fluoride
Citrate
Acid citrate dextrose
Oxalates
Iodoacetate

Question 11

What analytes require a mild base to be added to urine?

Answer 11

Porphyrins, urobilinogen, uric acid

Question 12

What urine analytes commonly require acidification?

Answer 12

Calcium, steroids, adrenaline, noradrenaline and vanillylmandelic acid

Question 13

What analyte will precipitate if urine is acidified?

Answer 13

Uric acid/urate

Question 14

How do fibrin clots form in serum samples?

Answer 14

If spun and separated prematurely

Question 15

Pre-analytical factors to consider in potassium measurement

Answer 15

1. Serum K higher than plasma due to platelet rupture during clotting
2. Haemolysis
3. Delayed separation, particularly if sample refrigerated (Na-K ATPase inhibited)
4. Extreme leukocytosis eg CLL causing pseudohyperkalaemia due to WBC rupture or AML causing pseudohypokalaemia due to increased Na-K ATPas activity
5. Fist clenching with tourniquet - muscle K+ efflux into plasma

Question 16

Advantages of plasma over serum?

Answer 16

1. More rapid TAT - don’t have to wait for tube to clot
2. Suitable if in vivo haemolysis suspected