SIP

Subject Title: Clinical Chemistry
Topic: Blood Gas Testing

Heys..I have been attached to clinical chemistry lab for the whole of my SIP. In this lab, there are 5 workstations. I had been posted to blood gas station for 2 weeks. I had learnt to use Roche Omni Cobas b 221 system for testing blood gases. This analyzer can measure analytes such as pH, pO2, pCO2, electrolyte ISE(e.g.Ca2+),total haemoglobin, oxyhaemoglobin, carboxyhaemoglobin, methemoglobin and O2 saturation. It consists of reagents such as S1 Rinse Solution, S2 Fluid Pack Solution and waste blood container.

Principle of Measurement
O2: use of clark measurement principle. It is the measurement of current generated by reduction of O2
CO2: measurement of pH change in electrode caused by CO2
pH and Ca2+: potentiometric electrodes based on the measurement of a potential under no current flow. Calculation of these require use of reference electrode
Total haemoglobin: light absorption in whole blood measured at different wavelengths

Calibration, QC, Maintenance
Calibration, quality control and maintenance need to be done before running any patient's samples. Everyday in the morning, calibration results, which include system cal, 1 point cal and 2 point cal, need to be printed out and filed for future audits. Calibrators are not required as the analyzer will automatically calibrate by itself in time intervals. This will plot out a calibration curve and to determine any errors in the measurement of the analyzer so that is adjusted to show true values. After that, quality controls need to be done to ensure the results are within the control limits. QC is performed daily at 9am and 4pm. The commercial control ampoules are stored at 2-8 degree celsius and are temperature sensitive. Hence, it has to "grip warm" in the palm for about 10min before running to achieve successful QC results. The results will also have to be filed. Lastly, maintenance has to be done to make sure it is in good condition. This includes:
- Checking thermal paper supply
- Checking reagents level
- Cleaning the fill port(where the blood is pumped in)with wet cotton swab for removing blood stains
Now, the analyzer will be ready to run patient's samples. These samples are collected in heparinzed syringe which contains anticoagulant to prevent clotting of blood

Procedures
1)Stamp time for the patient's sample
2)Ensure is sent in ice bag
3)Label barcode on both the syringe and request form
4)Order tests requested into LIS
5)Mix the syringe well and check for blood clots before pumping into analyzer
6)Check the analyzer is at ready mode and having green signal before pumping
7)Pump blood into analyzer
8)Scan barcode

Test Results
Analytes-------- Reference Range
pH--------------> 7.350-7.450
pCO2------------> 35.0-45.0 mmHg
pO2-------------> 75.0-100.0 mmHg
O2 saturation---> 95.0-100.0%
Ca2+------------> 1.140-1.320 mmol/L
Total haemoglobin---> 11.5-17.4 g/dL
Oxyhaemoglobin------> 95.0-99.0%
Carboxyhaemoglobin--> 0.5-2.5%
Methemoglobin-------> 0.0-1.5%

Clinical Interpretation
After the results are out, we have to check for any abnormal high or low levels which will be flagged red in the LIS. For example if the pH is less than 7.1 and pCO2 is more than 45 mmHg, we need to call the nurse to inform these panic values. This shows that the patient is having respiratory acidosis. If there is abnormal high pCO2, we have to check if blood sample appear dark and re-run the test. Always ensure pO2 is directly proportionally to O2 saturation. After verifying the results, we can file them into LIS. Therefore, blood gas testing is for diagnostic and therapeutic reasons

That's all for now. Enjoy your SIP!
Soong Ci Liang
0503333G
TG01