The implementation into clinical practice of syndromic testing by multiplex polymerase chain reaction allows early etiological diagnosis and paves the way towards timely targeted treatment. However, there is stringent need for diagnostic stewardship, as multiplex testing can also come with a high risk of misdiagnosis if improperly ordered or interpreted. We report two cases that illustrate proper and improper diagnostic stewardship, having important implications for correct patient management and application of antimicrobial stewardship into current clinical practice.