PreanalyticalErrors in Troponin TestingBy Leo Luk

Three Stages of Laboratory TestingPre Analytical

Specimen Collection, Transport and Processing

Analytical

Testing

Post Analytical

Result Interpretation, Storage and retesting

Preanalytical Factors in Immunoassays

Patient Medical History

Patient Identification

Serum and Plasma

Filling and Mixing

Preanalytical Factors in Immunoassays (Continued)

Fibrin Interference

Sample Processing

Heparin

Biotin

Troponin

• Troponin is the specific marker used for myocardial injury.

• The concentration in blood is the key for diagnosing acute coronary syndrome.

• Troponin T

• Troponin I

• Troponin C

Case Scenario

A clinician phoned up to query two Troponin T results from two different patients. Both were run on the same analyser.

Instrument platform:

Cobas 8100 automated workflow series

Cobas 8000 modular analyser series

Patient A

Result from 02:35 of 29 was suspicious

On Repeat patient A was 6.64, 5.58 and 4.36 which fit as expected results.

Patient B

Result from 02:00 of 40 was suspicious

Patient B repeated as 16.5, 15.2 and 15.5 which also fit as expected results.

Hs Troponin T

Time 10:26 20:05 02:00 06:30 10:40

Result 15 17 40 17 14

Analytical Error?

Both Suspicious results were generated from

the same analyser

There were no instrument flags on any results, only these two samples were affected.

There was no lot change of reagent

All Internal Quality Controls were good on

e801 module.

Investigation

• Precision of 20 samples of 17.1 was 1.8%

• Cobas 8000 was set up to run samples in duplicate if results were > 14ng/L

• Duplicate sample results await manual validation by a Scientist.

• When duplicate results do not correlate, repeat troponin tests are run on a second cobas 8000.

Investigation (Continued)• Roche was notified

• With further investigation, it was noted that multiple discrepant results were from the first cobas 8000. Whereas one discrepancy was from the second cobas 8000.

• Precicontrol TN was then run for one week

• Roche Germany confirmed no errors on the Cobas 8000 during that period

Preanalytical Error?

Duplicates been turned off and comment to be added:

“Rarely falsely high or low troponin results can occur due to analytical interferences (e.g. macrotroponin, high dose biotin, fibrin microclots in the sample). Sample should be inverted at least several times after collection, and an intake of biotin within the last 8 hours noted. If a troponin result does not fit the clinical pictures, please contact the laboratory.”

PreanalyticalError? (Continued)

Both specimens were collected in Lithium Heparin tube

Collected by different people and from different wards

Arrived through pneumatic tube system

Factors Impacting Heparin-Plasma Specimen Quality and Overall Performance

1 Patient Disease StateMedication

2 Specimen before laboratory Tube Type (gel/non-gel)Phlebotomy techniqueInadequate mixingTransport time and conditions

3 Specimen in laboratory Centrifugation conditionsHandling after centrifugation (aliquoting, mixing)Storage time and temperature

4 Instrument Probe depth/diameterPredilutionReagent pHAutomation, transport belt (agitation)

Improper Mixing After Specimen Collection

• During investigation, we confirmed there were no malfunctions on Cobas8000 instruments

• After specimen arrival to the laboratory, samples are registered by staff and loaded on to the Cobas 8100.• Centrifuge

• Aliquot

• Transport to Cobas 8000

• Improper mixing during collection was the likely cause.

Instrument/Assay Considerations

Cells, platelets and other components in heparin plasma may cause issues in the instrument.

• Sampling probe blockage

• Cells in the sample rupture due to reagent pH change

• Optical interference

Why is Troponin an issue now?

The need for earlier and faster detection of diagnostic markers has driven manufacturers to make their systems more rapid and sensitive.

The advancement of technology has increased the sensitivity of troponin testing, however, along with this advancement, specimen quality is now more important than ever

Conclusion

• It is rare to encounter spurious Troponin result

• Promotes staff awareness of preanalytical error

• Stay vigilant about inappropriate results

• Contact manufacturer when issues occur

Reference

Pretorius, C. J., Dimeski, G., O'Rourke, P. K., Marquart, L., Tyack, S. A., Wilgen, U., & Ungerer, J. P. (2011). Outliers as a cause of false cardiac troponin results: investigating the robustness of 4 contemporary assays. Clinical chemistry, 57(5), 710-718.

Herman, D. S., Kavsak, P. A., & Greene, D. N. (2017). Variability and Error in Cardiac Troponin TestingAn ACLPS Critical Review. American journal of clinical pathology, 148(4), 281-295.

Lippi, G., Salvagno, G. L., Montagnana, M., Franchini, M., & Guidi, G. C. (2006). Phlebotomy issues and quality improvement in results of laboratory testing. Clinical laboratory, 52(5-6), 217-230.

Reichstein, E. (2003). The Importance of Preanalytical Factors in Immunodiagnostic Testing. EJIFCC, 14(3), 124.

Acknowledgement

Thanks everyone from ALSS for technical support and love

Carol Siu, Chemical Pathologist for professional guidance