Laboratory and Diagnostic Testing
Core concepts
This domain covers specimen collection, handling, and interpretation basics. Know the pre-analytic variables that affect results: fasting status, timing, tourniquet time, hemolysis, tube order, and proper labeling. Understand common tests (complete blood count, basic metabolic panel, coagulation studies, cultures, urinalysis, glucose) and what an abnormal value generally signals. Know the difference between screening, diagnostic, and monitoring tests, and why reference ranges vary. Familiarity with imaging preparation (contrast, fasting, metal screening) and point-of-care testing quality controls is expected.
Traps
Distractors blame the patient or the analyzer when the real issue is collection technique - for example, a hemolyzed sample from a traumatic draw or a falsely elevated potassium from prolonged tourniquet time. Labeling errors are a classic: an unlabeled or mislabeled specimen must be rejected, not "fixed" by adding a label later. Watch for questions that confuse a critical value with a normal variant, and for answers that skip notifying the provider of a critical result.
Rule of thumb
Pre-analytic-first rule: when a result seems impossible, suspect the collection before the disease. Ask about fasting, timing, hemolysis, and labeling first.
Worked example
A potassium result is unexpectedly high in a well patient. Before treating, consider hemolysis or a prolonged tourniquet - recheck with a clean, atraumatic draw. If the value is confirmed critical, notify the provider promptly and document the notification.