▶What is a reference range and what does it mean when a result falls outside it?
A reference range (or normal range) is the interval of test values measured in a healthy population, typically the central 95% of results. Ranges vary by age, sex, and population; an infant's potassium range differs from an adult's, and hemoglobin varies by male/female. When a result falls outside the range, it is flagged as abnormal (high or low) and may trigger a reflex test or alert to the clinician. However, abnormal does not always mean disease: some healthy individuals have naturally high or low values. Context matters: a glucose of 110 mg/dL is high but expected after a meal, whereas 250 fasting suggests diabetes. You must know the patient's clinical picture, medications, specimen quality, and timing before interpreting. Borderline abnormal values may require repeat testing or delta checking (comparing to previous results) to assess significance.
▶What is a delta check and why do laboratories perform them?
A delta check is a comparison of a patient's current result to their previous result to detect sudden, clinically impossible, or instrument-error changes. Example: if a patient's potassium was 4.2 mEq/L last week and today's sample is 7.0 mEq/L with no clinical intervention, that 2.8-point jump is impossible in minutes and signals a problem. Delta-check systems flag such changes automatically, prompting the lab tech to investigate before reporting. Common causes: hemolysis (ruptured RBCs leak potassium), specimen mislabeling, patient misidentification, or instrument malfunction. The tech may repeat the test, visually inspect the specimen, or contact the phlebotomist to redraw. Critical delta checks may not report until verified. Delta checking is a safety net that catches errors before they reach the clinician and potentially harm the patient.
▶What is hemolysis, lipemia, and icterus, and how do they affect results?
These are the three main pre-analytical variables (specimen quality problems before analysis). Hemolysis is rupture of red blood cells, releasing intracellular potassium, LDH, AST, and other enzymes into serum, falsely elevating results. Cause: prolonged tourniquet time, vigorous tube shaking, small-gauge needle, or difficult draw from a hematoma. Lipemia is excess lipid (cholesterol, triglycerides) in serum, making it cloudy. Cause: non-fasting state, high triglycerides, or liver disease. Icterus is excess bilirubin (yellowing), seen in jaundice. These three interfere with optical absorbance on analyzers: hemolysis and lipemia absorb light, skewing results. Some tests are stable despite interference (potassium in hemolyzed serum is actually valid), while others are invalid (glucose in lipemic serum can falsely rise or fall). Modern analyzers measure and flag these interferences automatically. If flagged, the lab may report results with a comment, reflex to a diluted sample, or request a redraw. Understanding which tests are affected by which interferences prevents clinical errors.
▶What are critical values and how do they guide clinical action?
Critical values (panic values) are results that indicate life-threatening conditions requiring immediate physician notification, often within 15–30 minutes. Examples: glucose <40 or >600 mg/dL (risk of seizure or coma), potassium <2.5 or >6.5 mEq/L (cardiac arrhythmia), calcium <6.5 or >13 mg/dL (tetany or coma), pH <7.2 or >7.7 (acidosis or alkalosis), or troponin >0.1 ng/mL (myocardial infarction). Labs establish critical-value thresholds, and many LIS systems automatically alert and prevent result reporting until a clinician acknowledges the call. The lab tech must call the ward nurse or resident immediately, provide the patient name, critical value, and test name, and document the time and person notified. A delayed or missed critical-value call is a patient safety sentinel event. Understanding which values are critical and the urgency of notification is essential.
▶How do you interpret a complete blood count (CBC) and what patterns suggest disease?
A CBC measures white blood cells (WBC), red blood cells (RBC), hemoglobin (Hgb), hematocrit (Hct), platelets, and red cell indices (MCV, MCH, MCHC). Patterns tell a story: low RBC + low Hgb + low Hct = anemia (suspect iron deficiency, B12 deficiency, bone marrow failure, or chronic disease). High WBC = infection, leukemia, or stress. Low WBC = bone marrow suppression, infection overwhelming the immune system, or medications. Low platelets = bleeding risk, sepsis, or immune destruction. MCV (mean corpuscular volume) classifies anemia: MCV <80 = microcytic (iron deficiency), MCV 80–100 = normocytic (acute bleeding, hemolysis, bone marrow disease), MCV >100 = macrocytic (B12 deficiency, folate deficiency, alcohol). A left shift (immature bands >5%) signals acute infection. Blasts in a normal CBC may indicate leukemia. You must know normal ranges for age (infants have high RBC; children have high WBC). Correlate the CBC with the patient's clinical presentation and other tests to narrow the differential.
▶What is the difference between a qualitative result and a quantitative result, and when is each used?
A qualitative result is positive, negative, present, or absent — no numeric value. Examples: pregnancy test, blood culture (organism identified or not), urine dipstick for protein (trace, 1+, 2+, 3+, or 4+). Qualitative tests answer 'Is this condition/organism present?' Quantitative results are numeric values (hemoglobin 13.5 g/dL, glucose 95 mg/dL) that reflect the amount or concentration of the analyte. Quantitative tests are more informative but also more labor-intensive. Some tests report both: a pregnancy test may be qualitative (positive/negative) or quantitative (hCG level in IU/L, useful for dating pregnancy or detecting ectopic pregnancy). Qualitative tests are faster and cheaper but less precise; quantitative tests guide treatment decisions (do we escalate therapy based on a higher troponin, or is the value borderline?). Modern labs favor quantitative methods when possible for precision and prognostication.
▶How do you handle and report an out-of-order (OOO) result or suspect a pre-analytical error?
When a result is illogical, unexpected, or contradicts the patient's clinical status, first do not report it. Instead: (1) Check the specimen quality: is it hemolyzed, clotted (if serum was needed), too dilute, or contaminated? If yes, request a redraw. (2) Verify patient ID: is the label correct and matched to the requisition? If no match, flag for investigation before release. (3) Review the delta check: does today's result match the patient's trend? A sudden shift may trigger a repeat. (4) Re-run the analyzer: some instruments flag carry-over or calibration drift; retest on a fresh sample. (5) Contact the clinician: if all checks pass and the result is still unusual, call to verify the patient status and specimen collection time. (6) Document the investigation: note why the result was questioned and what corrective action was taken. Never assume a result is correct because the machine printed it; clinical labs are a team sport, and the tech is the last check before harm.
