A patient's blood sample tests negative on a direct antiglobulin test. After adding Coombs control cells and observing no agglutination, what should be concluded?

In this scenario, when a direct antiglobulin test (DAT) yields a negative result and there is no agglutination observed even after the addition of Coombs control cells, it indicates an issue with the test procedure. The Coombs control cells are used to ensure that the testing reagents are functioning properly. Their purpose is to help confirm that the test results are valid.

If the Coombs control cells do not show agglutination, it suggests that there may be a problem with the testing process, such as inadequate reagents or improper technique. Therefore, it is essential to repeat the test to ensure accurate results, as a negative result with control cells also negative does not provide reliable information about the patient's condition. This step is critical in clinical settings to avoid misdiagnosis and ensure patient safety.

Further testing being unnecessary would contradict the need for accuracy and reliability in testing, and assuming normal reactions without confirmation would be premature.