Delvotest® Milk Controls are highly reliable when used correctly, but like any tool, issues can arise that affect their performance. This guide covers the most common problems users face, providing clear steps to troubleshoot. In this article, we’ll cover:
- Positive controls testing negative
- Negative controls testing positive
- Controls not dissolving properly
- Inconsistent expiration dates on vials and boxes
Positive Control Testing Negative
When a positive control yields a negative result, it indicates an issue that needs to be resolved promptly. Here are some common reasons for this issue and how to troubleshoot them — which we advise to systematically troubleshoot each factor to identify the root cause:
- Expired or Degraded Control. Check the expiration date of the positive control. If it’s expired or improperly stored, obtain a fresh control.
- Contamination. Ensure proper sterility procedures are followed. Use fresh sterile materials and double-check your own application protocols.
- Errors in Preparation. Make sure the positive control was prepared correctly. Even minor deviations in preparation can lead to inaccurate results.
- Instrument Malfunction. Ensure your equipment is functioning correctly and has been calibrated according to manufacturer guidelines.
- Cross-reactivity. Consider using alternative controls if cross-reactivity is suspected. Review the specificity of your test to ensure accurate results.
Negative Control Testing Positive
A negative control should never test positive. If it does, there are several potential reasons to investigate:
- Contamination. Contamination during sample preparation or testing is the most common cause of a false positive. Ensure proper sterilisation and handling techniques.
- Storage Issues. Improper storage of the control can lead to degradation. Verify the control was stored in 2–8°C, away from light.
- Reagent Quality. Ensure that all reagents used in the test have not expired and have been stored properly.
- Instrumentation Issues. Perform regular maintenance checks on your equipment and validate the test performance periodically to avoid false positives.
Once you’ve identified the likely cause, take corrective action by repeating the test with fresh negative controls, validating your equipment, and improving handling practices.
Issues with Dissolving the Controls
If your milk controls are not dissolving properly, follow these steps to address the issue:
- Agitate with a Stirrer. If the controls don’t dissolve after inverting the bottle c. twenty times, use a magnetic stirrer. Ensure the stirrer is clean to avoid contamination.
- Check the Expiration Date. Ensure the controls are within their expiration date. Expired controls may not dissolve properly.
- Water Quality. Ensure you are using distilled or demineralised water for reconstitution. Contaminants in the water can interfere with the dissolution process.
Inconsistent Expiration Dates
Occasionally, users may notice a discrepancy between the expiration date on their Delvotest® Milk Control vial and the date on the box or order. This issue is most common with batches of goat and sheep controls. The shelf life for all Delvotest® Milk Controls is five years when stored under the recommended conditions (2–8°C, away from light). In some cases, batches of goat and sheep controls were given a shelf life extension after production, but the existing stock may not have been relabelled. However, the manufacturing date is clearly stated on each vial, and the expiry should always be based 5 years after this date. If the expiration on the vial and box are inconsistent, always refer to the manufacturing date on the vial.
Summary
Delvotest® Milk Controls are key to ensuring accurate and reliable antibiotic residue testing. However, even with proper usage, though extremely rare, issues such as inconsistent expiration dates, unexpected test results, or difficulties with dissolving the controls can occur. By following the troubleshooting steps in this guide, you can identify and resolve the most common issues quickly, ensuring your controls remain reliable and effective for all your testing needs.