Star Team

Hello. It is the end of the second week. I am having lots of fun in Biochem lab. =) ... we had a fire drill just yesterday and attended a staff meeting! and so far we have gone for two tutorials on LIS and Lab Safety. Not going to elaborate on that as i think everyone knows what it is about already. The five of us was split into 5 stations and we will be rotating every 2 weeks. For the last 2 weeks, i was posted to Station A (DD). Beckman Coulter Unicel DXI is one of the analyzer in Station A (DD). The other analyzer used is DTSCII and DT60II. In this post, I will elaborate on DXI.

Quantity can be determined for Serum ferritin, folate, RBC folate, Vitamin B12, Cortisol, Urine Cortisol, PTH, testosterone, D-HEAS and BHCG using DXI. It is a little similar to the analyzer in school that we used during practical. DXI has a continuous loading capability and approximately 120 samples can be loaded at once. Racks can be loaded directly from the centrifuge and is released in less than 5 minutes for other testing. This increases productivity and efficiency. When loading into analyzer, the sample must be checked for fibrin clots. Amount of plasma must be above 1cm, if not, it must be transferred to a plastic tube. DXI uses paramagnetic particle chemiluminescent immunoassay for quantitative determination. Light generated by the reaction is measured with a luminometer. Amount of analyte in the sample is determined from a stored, multipoint calibration curve. If results are too high, dilution is required. DXI has an on board dilution for ferritin. If after dilution, it is still high, do 3X manual dilution. Folate and B12 do not require dilution. The rest is manually diluted with either saline or SO calibrator.

Calibration is done once a month, when a new lot of reagent is used, on expiry, QC is unacceptable or after major maintenance procedures or replacement of parts. Calibration determines the relation between the result and the value of the input quantity.

Maintenance
1. Backup System
There is an auto system backup at 5am.
The cartridge is changed daily in case of breakdown.
2. Back up daily data system
3. Check inventory
Loading bulk supplies
-Substrate- equilibrated to room temperature under reagent load door, able to remain at room temp for 14days.
-Wash buffer- used to dilute samples/reagent, wash away unbound materials in RVs, wash pipettor probes and prime system.
-Reaction Vessels- store samples on board, prepare sample dilution, incubate sample with assay specific reagent during processing.
-Liquid waste generated when- pipettors are washed between processing steps and when unreactive fluid are washed into RV.
-Solid waste- collect empty reagent packs, used RVs, and condensation during processing.
-Reagent- If test not done so often, don’t keep adding reagent – not fresh.
4. Record test count of previous day
5. Shake solid waste container – radioactive wastebag is used
6. Run daily special clean routine – not the normal cleaning because Vitamin B12 reagent is sticky. Contrad, Citranox, Methanol 70%

Quality control is important and has to be done daily to keep the analyzers in top condition and results produced are accurate and precise. Charts are compared and if controls are not within the 2SD mean, QC must be done again.

Biorad Lyphocheck Immunoassay Plus Control Levels 1- 3 and PTH Control Levels 1-3 are done daily. PTH control is run twice as it is running 24hrs. Controls are parafilmed and stored in the fridge to prevent deterioration of the constituents. Liquickek Urine Chemistry Control Levels 1- 2 for Urine free Cortisol and RBC folate Control Levels 1- 3 are done when needed. If 2 out of 3 controls are in, patient samples can be loaded.


Principles
1. Ferritin- two site immunoenzymatic “sandwich” assay. Light production is directly proportional to concentration of ferritin.

2. Vitamin B12- competitive binding immunoenymatic assay. Photon production is inversely proportional to concentration of ferritin.

3. PTH – two site immunoenzymatic “sandwich” assay. Light production is directly proportional to concentration of ferritin.

4. DHEA- competitive binding immunoenzymatic assay. Light production is inversely proportional to concentration of ferritin.

5. Testosterone - competitive binding immunoenzymatic assay. Light production is inversely proportional to concentration of ferritin.

6. Cortisol- competitive binding immunoenzymatic assay. Light production is inversely proportional to concentration of ferritin.

- Serum cortisol
- 24hr Urine free Cortisol- Two sets of controls are used in case the first set is out of range. Ethyl acetate is added which produce two distinct layers as acetate density is lighter. It is used to extract cortisol from urine. 200ul is pipetted out from the top layer and left overnight in the fumehood to dry up. SO calibrator acts as a diluent to dissolve the precipitated cortisol. Run 1 set of control first. This reduces cost as a bottle of SO calibrator is very expensive. If not within range, use second set of control. If within range, run patient sample on DXI. Procedures are done in fume hood as acetate has a strong odour and is carcinogenic. Glass tubes are used as plastic react with acetate. As glass tubes are used, centrifuge speed is 2500 rpm to prevent breakage.

7. Folate- competitive binding receptor assay. Light production is inversely proportional to concentration of ferritin.

- Serum or Plasma (heparin) Folate – do not use hemolysed sample. Folate level in red cell is much greater than serum or plasma, lead to spuriously high results.
- RBC folate – contains EDTA- prevent clotting – whole blood or plasma. Specimen sent to Haem lab for HCT. Lysing solution added to release folate in RBC from endogenous binding proteins. Placed in cupboard for 1 ½ hrs as lysing solution and the lysing reaction is light sensitive. Run controls to see if they are within range before loading patient samples.


Thats all for now.

Jo-anne
TGO2
0503324F