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Chem Path > L2 Pre analytical errors > Flashcards

L2 Pre analytical errors Flashcards

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1
Q

What is the possible biological variable of creatinine?

A
  • Creatinine is lower in the elderly (age)

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

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2
Q

Possible biological variable in pregnancy?

A
  • increase in intravascular volume, hormonal changes
  • albumin is lower due to dilution
    > pregnancy-specific reference interval
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3
Q

List the possible cyclic variations.

and how to correct them

A
  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
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4
Q

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

A

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

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5
Q

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

A

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
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6
Q

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

A
  • Cr, ALT

- may cause pseudohyponatremia (elevated triglyceride)

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7
Q

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

A
  1. Thyroxine, iron intake

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

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8
Q

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

A
  • increase muscle content (CK, LDH, AST)
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9
Q

How posture can affect lab result?

A

Standing

  1. Blood pools in LL, increased protein and protein-bound substances in the blood
  2. Decreased plasma volume > stimulate RAAS
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10
Q

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

A

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

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11
Q

What can be the possible effect of using a tourniquet?

A
  • Application > 1 min will cause occlusion!

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

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12
Q

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

A

Venous blood

  • less PO2
  • more PCO2
  • more HCO3
  • lower pH
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13
Q

What is drip arm? (1)

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

A

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
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14
Q

What is the order of draw when using collecting tubes?

A

白 藍紅綠紫灰

> to prevent carryover od additives

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15
Q

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

A

Trace metals

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16
Q

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

A

Clotting profile

17
Q

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

A
  1. Drugs
  2. Tumor markers
  3. Most hormones
18
Q

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

A
  1. L/RFT
  2. CaPO4
  3. Urate
  4. CK
  5. LDH
  6. GGT
19
Q

The EDTA (purple tube) is for collecting?

A
  1. CBC

2. HbA1C

20
Q

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

A

plasma glucose

21
Q

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

A
  1. increased K+ (contamination)
  2. reduced Ca2+ (chelation)
  3. reduced ALP (chelation of Zn, Mg - essential cofactors for ALP activity)
22
Q

Heparinized syringe is for ABG and ionised calcium.

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

A

> 10%

  • decrease in pH
  • increase in PO2

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

23
Q

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

A

ice bath

24
Q

How can air bubble interfere with lab results.

How to prevent it?

A
  • increase in PO2
  • decrease in PCO2
  • Tap the syringe to remove the bubble
25
Q

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

A
  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
26
Q

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

A
  1. Transportation time

2. Transportation method

27
Q

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

A
  1. metabolism continues (increase CO2, H+, lactate, reduced glucose, O2)
  2. after O2 consumption -> release cellular content (K+, LDH, AST)
28
Q

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

General solution?

A

proteolysis of peptide hormones

  • ice-water bath
29
Q

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.

A

Hemolysis;

Warm sand, thermos

30
Q

The blood sample shows hyperkalemia.

Possible pre-analytical errors?

A

Pre-collection

  1. Wrong patient
  2. Underlying renal disease
  3. Medications

Collection

  1. Hemolysis
  2. Contamination - K3 EDTA

Post collection
6. Prolonged storage

31
Q

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

A

Likely K3 EDTA contamination

Chem Path (15 decks)

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