Lab Test Questions: Troubleshooting Unusual Troponin Test Results

Question Submission:"I'm a medical laboratory scientist working in a rural hospital. We've been seeing some unusual results on our chemistry analyzer for troponin levels that seem inconsistent with patient presentations. The QC results look fine, but I'm concerned about potential interference or calibration drift. What troubleshooting steps should I take to validate these results before reporting them to clinicians?"

Joseph Indovina: As someone who helped develop a troponin assay for a major in vitro diagnostic company, the following may be helpful. I will approach the suggestions as if your clinical laboratory is using a high-sensitivity troponin. The approach is similar to a non–high-sensitivity troponin assay.

Calibration drift: You mentioned that the quality control results look fine. Current guidelines emphasize the use of three-level QC material. The three levels cover the limit of detection (level 1), the upper end of the 99th percentile (level 2), and a third level in the upper AMR. If you are not using three levels, consider implementing them. If you are using three levels and there is no evidence of quality control drift, then calibration stability is fine.

Proof source for three level control strategy: View PubMed Resource

Assay within lab precision: Inspect the actual within-lab quality control precision and verify it is meeting the assay vendor's published data. These will be found in the assay Instructions For Use. Further comparative data may be found with the quality control fluid peer group data. If your assay within lab precision is not consistent, then this needs to be investigated. Areas to consider include fluid preparation, which includes handling, QC vial-to-vial inconsistency, and inspecting the within-lab QC for outliers.

The unusual results: there are several areas to consider. The first place I start with is: Check that the initial patient result is reproducible i.e. is it an outlier or not.

If the patient sample is not reproducible (it is an outlier):

1) Check the sample itself. Is the centrifugation process following the tube vendors' requirements? The most common cause that I found was using a higher G force than required and a shorter spin time. This is performed to improve turnaround time. Unfortunately, with gel tubes, this causes issues with proper gel setup. The tube vendor Instructions For Use will have the proper requirements. There are several online tools to help calculate G force.

One is found here: Open G-Force Calculator

If the G force is above specification, this may impact how the gel sets up the barrier in the tube. A consultation with the tube vendor is also helpful.

2) Verify instrument maintenance is up to date.

3) Perform a within-run precision check. This is done by running several cups of the same quality control fluid. A common test I used was 10 cups and 2 replicates per cup. At the end of the run I inspect the data for any evidence of outliers. I then calculate the mean, sd, and CV and compare to the assay Instructions For Use precision table.

If the patient sample is reproducible: Is the result elevated above the 99th percentile and, over a time series, consistently elevated? In the case of the patient having consistently elevated results during the presentation and the results are consistent, this could be one of two possibilities: an interferent called macro troponin or the second possibility a heterophile antibody. These are rare yet are observed.

With a macro troponin, the body's immune system makes antibodies against the troponin protein. This becomes a large complex structure and remains in the body for a prolonged period. One troubleshooting step is pretreating the sample with polyethylene glycol. This will precipitate the macro. Next re run the sample. If the troponin is lower than it is likely a macro troponin.

Since this is only for troubleshooting and is not a validated result, the lab director needs to be involved.

For heterophile antibodies, these too will cause a persistent false elevation. To troubleshoot a possible heterophile, repeat the sample on a different platform. If the sample result is lower than it is likely a heterophile. There are also heterophile blocking tubes laboratories may purchase to pretreat the sample.

Non-cardiac causes of troponin release: This is a good place to refresh that troponin is released when there is an insult to the cardiac muscle however, it is not always due to a cardiac infarct. A very good resource is found here: Read ACC Article

In summary, when presented with unusual results on your chemistry analyzer for troponin levels that seem inconsistent with patient presentations, there are several steps one could take. The first and quickest is repeating the sample. The above provides steps to take if the samples does or does not repeat. Deeper troubleshooting steps are also provided, which include a close examination of quality control. Finally non-acute coronary syndrome (ACS) troponin increases are possible. I have provided a resource.

Diagnostic Equity Resources:

Are There Diagnostic Testing Inequities in Rural Areas?
URL: https://diagnosticequity.org/discovery-hub/are-there-diagnostic-testing-inequities-in-rural-areas

Why Am I Always Tired? Lab Tests That Explain Fatigue
URL: https://diagnosticequity.org/discovery-hub/why-am-i-always-tired-lab-tests-that-explain-fatigue