The customer has tested 1 patient with tobr2 tobramycin (tobr2) on a cobas 6000 series system, tobr tobramycin (tobr) on a cobas integra system and the abbott tobramycin assay on an architect system.
The customer provided results from the patient obtained between (b)(6) 2015 and (b)(6) 2017.
The customer is questioning the tobr2 results from the cobas 6000 series system because they are consistently higher even after stopping tobramycin treatment and without the patient showing any symptoms of toxicity.
The customer thinks the tobr results from the integra system are correct.
Based on the data provided, comparison results on (b)(6) 2015 between the tobr2 assay on the cobas 6000 system and the tobr assay on the cobas integra system were erroneous.
Refer to attached data for a chronological list of the patient test results, specific treatment received and patient weight at time of test if available.
There was no allegation that an adverse event occurred.
The customer believes there is an interferent in the patient sample affecting the results.
The customer performed a series of investigations in an attempt to identify the interference.
Refer to the attached data for the details of the customer¿s investigation.
All the samples from the patient were taken at trough level.
Some patient results were from finger stick tests and some patient results were from venous samples.
It is not clear which results are from venous samples and which results are from finger sticks.
Peak level samples are not monitored by the customer.
The customer declines to provide calibration or quality control (qc) data as they don¿t believe this is a method quality issue.
A specific root cause could not be identified.
Additional information was requested for investigation but was not provided.
Two assays, the tobr2 with c6000 system and the tobramycin assay with the architect system are competitive immunoassay methods; one utilizing a polyclonal, and the other a monoclonal capture antibody, respectively.
Only the competitive tobr assay with the integra system employing a monoclonal ab, seemed to produce the negative results expected for this patient.
Since qc has been acceptable, analytical and pre-analytical quality issues have been excluded.
The investigation stated an unknown substance is interfering with the tobr2 assay, however, since the patient sample is not available, this cannot be confirmed.
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