Patient Care Decision Making and Consultation
Core concepts
The laboratory professional is a consultant. Know how to interpret and communicate results: critical value reporting, call-back thresholds, and the difference between preliminary and final results. Understand stewardship - the laboratory's role in promoting appropriate test ordering and antimicrobial use. Know when to recommend additional testing (e.g., reflex cultures, susceptibility panels, confirmatory tests) and when to question a result that doesn't fit the clinical picture.
Understand test performance: sensitivity, specificity, positive and negative predictive value, and how prevalence affects PPV. Recognize that a highly sensitive test is best for ruling out disease, and a highly specific test for ruling in. Know the importance of turnaround time in clinical decisions (sepsis, meningitis).
Traps to expect
- Confusing sensitivity with PPV - PPV depends on prevalence.
- Forgetting that critical values require timely notification and documentation.
- Assuming a positive test always means disease - pretest probability matters.
- Overlooking that stewardship includes diagnostic stewardship (right test, right patient, right time).
Worked example / rule of thumb
A patient with low pretest probability for bacteremia has a single positive blood culture with a coagulase-negative staphylococcus. Rule of thumb: consider contamination - CoNS is a common skin contaminant. Recommend a second culture and clinical correlation before treating. This is diagnostic stewardship in action.