9.1 The Total Testing Process: Preanalytical, Analytical & Postanalytical Quality

The Total Testing Process: Preanalytical, Analytical & Postanalytical Quality

The ASCP BOC devotes 15 to 20 percent of the H examination to Laboratory Operations, and the first listed sub-topic is quality assessment across the preanalytical, analytical, and postanalytical phases. Roughly 60 to 70 percent of laboratory errors originate before the specimen ever reaches an analyzer, which is why this phase carries the most examination weight.

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1. The Preanalytical Phase

Patient and Specimen Identification

Two independent patient identifiers are required (typically full name and date of birth or medical record number); the room number is never an acceptable identifier. Tubes are labeled at the bedside, after collection, in the patient's presence. An unlabeled or mislabeled specimen from an irretrievable source (cerebrospinal fluid, a bone marrow aspirate, an intraoperative specimen) is the one situation in which a recollection is impossible, so a documented re-identification procedure signed by the collector is used instead.

Order of Draw and Additive Carryover

The CLSI order of draw prevents additive carryover between tubes:

Carryover traps. EDTA drawn before a chemistry tube contaminates it with potassium and chelates calcium and magnesium, falsely raising potassium and lowering calcium. EDTA carryover into a coagulation tube prolongs the PT and APTT.

Fill Volume Errors

Common Preanalytical Interferences

Hemolysis (traumatic draw, small-bore needle, vigorous mixing), lipemia, icterus, cold agglutinins, EDTA-dependent platelet clumping, and prolonged tourniquet time causing hemoconcentration. Specimen stability limits matter: EDTA specimens should be analyzed within 24 hours refrigerated, but smears for differential are best made within 4 to 6 hours because storage artifact (vacuolated monocytes, nuclear pyknosis, crenation) accumulates rapidly.

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2. The Analytical Phase

The analytical phase begins when the specimen is aspirated. Its quality controls are calibration and calibration verification, daily and interval quality control, instrument maintenance and function checks, reagent lot verification and parallel testing, temperature and equipment monitoring, and documented corrective action. These are covered in detail in the next three sections.

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3. The Postanalytical Phase

Result Review, Autoverification, and Delta Checks

Autoverification releases results that fall inside predefined limits without human review; anything outside those rules is held for technologist review. A delta check compares the current result with the same patient's previous result and flags a physiologically improbable change. A hemoglobin that moves from 13.8 to 7.2 g/dL in six hours could be genuine bleeding, dilution from an intravenous line above the draw site, or a specimen mix-up; the last possibility must be excluded before the result is released.

Critical Value Reporting

Critical values require immediate direct verbal notification to a licensed caregiver with read-back of the patient identifiers and the result, and documentation of the date, exact time, the caller, and the recipient. Representative hematology critical values include hemoglobin below 6.0 g/dL, platelets below 20 x 10^9/L, WBC above 50.0 x 10^9/L or below 0.5 x 10^9/L, new blasts on a smear, positive malaria parasites, an INR above 5.0, and organisms seen in a sterile body fluid.

Corrected Reports and Turnaround Time

A corrected report must retain the original result, clearly identify it as corrected, and record who authorized the change. Turnaround time is monitored from collection (not from receipt) to result availability, since collection-to-receipt delay is itself a common failure point.

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4. The ASCP BOC Composite Reference Ranges

The H/SH content guideline publishes a single composite table and states that all corresponding laboratory values on the examination can be interpreted using these ranges. They are not provided during the examination, so they must be memorized. Values appear in both conventional and SI units.

A distinction worth knowing. The coagulation ranges in that guideline (PT 11.0-14.0 s, APTT 25.0-35.0 s, fibrinogen 160-415 mg/dL, thrombin time 21.0 s or less, factor activity 50-150%) are published for the SH examination only. On the H examination, coagulation reference values are supplied within the question when they are needed, so read each item's stated interval rather than assuming one.