Performance standards, Analyser & Assays

Question 1

What are “allowable limits of performance”?

Answer 1

It is the normal range for each component measured. e.g. +/- 3.0mmol/L for Cl means w/in +/- 3mmol/L from true value

Question 2

The allowable limits of performance for sodium is +/- 3.0 mmol/L. If a lab can measure plasma sodium with a SD of 3.0 mmol/L, is that satisfactory? Explain
your answer

Answer 2

No bc if 1 SD is 3mmol/L that means the range is 6mmol/L in total. To determine the required mmol/L of 1SD (so it fits the limit of +/- 3mmol/L) must calculate [allowable limit/4]. 
*/by 4 bc thats the total SD range if SD were to be 2SD (=cover 95% results) 
==> 3mmol/L / 4 => 0.75mmol/L (1SD)

Question 3

What is a proficiency program, when is it necessary and of what use is it?

Answer 3

• External Quality Assurance program
• Long-term QC that measures the the lab’s performance every month, & compares results with other labs
• compares analytes/ machine/ method used

Question 4

Compare the way we use internal and external QC programs.

Answer 4

EQA: Compares results of a lab w/ other labs - are using the same instrument / reagent. Done every month
Int. QC: monitors precision & accuracy of assay & analyser. Done daily

Question 5

What type of auto-analyzer would be required to measure a steroid present at a concentration of 12 pmol/L. In addition, what type of assay principle would be required, and what would the calibration curve look like? *

Answer 5

Sml [ ] require more sensitive method => Immunoassay, competitive assay (=inversely proportional relationship)

Question 6

How do titrimetric assays differ from competitive assays? *

Answer 6

Titrimetric: sample put first then incubated then add labelled Ag
Competitive: Sample Ag & labelled Ag added at same time

Question 7

Compare the different type of solid phases used by Roche Elecsys and Siemens Immulite assays.

Answer 7

Roche: Streptavidin coated magnetized beads
Siemens: Capture Aby coated on bead

Question 8

What does the term homogenous signify, and what advantage do these have compared to heterogenous methods

Answer 8

Homogenous: all in liquid state. Everything is added in reaction = easy to automate & faster (less sensitive)
Heterogenous: Solid & liquid state. Removal/wash steps = time consuming but more sensitive

Question 9

The Roche Elecsys system is subjects to two sources of interference that are not seen in most other sensitive immunometric assays. What are these?

Answer 9

• patients taking large doses of biotin (vit B7) = interfere

- Anti-ruthenium Aby in patient samples = false positives

Question 10

What are the two major auto-analyzer types in a clinical biochemistry laboratory and give an example of major differences in the analytical principles of the chemistries they employ

Answer 10

• General chemistry analysers: Larger MW e.g. proteins, smaller vol (paeditrician). Homogenous assay
• Immumoassay analysers: Smaller MW e.g. hormones. Heterogenous assay (specific)

Question 11

What is chemiluminescence, and how does it differ from fluorescence or light colorimetry, and why do immunoassays using chemiluminescence yield a higher sensitivity

Answer 11

• no light source bc a photon light emitted from reaction = higher sensitivity from high signal
• light emitted is being measured

Question 12

What is a dry chemistry analyzer?

Answer 12

• slides with layers of reagents (not use liquids)

Question 13

Difference b/w chemiluminescent assay and chemiluminometric assay

Answer 13

Chemiluminescent:
Chemiluminometric: use chemiluminescence report system

Question 14

Describe 2 errors in immunoassays (& suggest solutions if possible)

Answer 14

• hook effect: Excess Ag saturates capture & labelled Aby. Solution: 2-step assays
• interfering Aby from pts sample: pts Aby can cross link
  & block sites for Ag = false pos signals