Preanalytic, Analytic, and Postanalytic Quality Assessment

The testing cycle

The terms preanalytic, analytic, and postanalytic describe three connected phases. Current standards also use preexamination, examination, and postexamination for the same sequence.

Patient preparation and biologic variation

Patient state can change a measured concentration even when the collection and method perform correctly. Name any preparation that affects interpretation in the order and collection instructions.^{3,43 Centers for Medicare & Medicaid Services. State Operations Manual, Appendix C. 2026.4 Simundic AM, et al. Joint EFLM-COLABIOCLI recommendation for venous blood sampling. 2018.}

Specimen integrity and interference

An interference creates a clinically significant difference in a result because another substance or property of the specimen affects the measurement procedure. The direction and size of the effect depend on the analyte, concentration of the interferent, specimen matrix, reagent, analyzer, and calculation used. A normal serum or plasma specimen is clear and pale yellow. Hemolysis, icterus, and lipemia each change that appearance. Check the specimen at receipt and confirm with the analyzer indices. Because the effect depends on the method, a visible specimen change cannot support one correction factor across methods.^{2,102 Clinical and Laboratory Standards Institute. Handling, Transport, Processing, and Storage of Blood Specimens… 2023.10 Clinical and Laboratory Standards Institute. Interference Testing in Clinical Chemistry. 2018.}

Ordering, identification, and acceptability

Patient and specimen identification remain linked from the order through the final report. Use at least two person-specific identifiers and label the specimen container in the patient's presence. Never use a room number or physical location as an identifier.^{1,161 Clinical and Laboratory Standards Institute. Patient and Laboratory Specimen Identification Processes. 2024.16 The Joint Commission. Two patient identifiers. 2026.}

CLIA permits an oral test request when the laboratory solicits written or electronic authorization within 30 days and documents its effort to obtain it. A laboratory or institution may set a stricter local policy. The requisition and specimen must supply enough information to identify the patient, authorized requester, requested examination, specimen source when relevant, and collection date and time when those details affect testing.^{1717 Centers for Medicare & Medicaid Services. 42 CFR §§493.1105, 493.1241, 493.1242, 493.1256, and 493.1291. 2026.}

The laboratory or institution defines the turnaround expected for stat and as soon as possible requests. The collection and receipt times show whether the specimen met that local definition.

Written acceptability criteria list each defect, its consequence, and the action:

Blood collection tubes and order of draw

Whether a tube suits a test depends on its additive and the manufacturer's instructions. Stopper colors can vary. Current CLSI venous-collection guidance uses this sequence to limit additive carryover: blood culture, sodium citrate, serum, heparin, EDTA, then glycolytic inhibitor.^{21,2221 Clinical and Laboratory Standards Institute. Order of blood draw tubes and additives. 2019.22 Clinical and Laboratory Standards Institute. Collection of Diagnostic Venous Blood Specimens. 2025.}

Fill additive tubes to the required volume and mix them by the tube manufacturer's gentle inversion schedule. Shaking can damage cells. Delayed or inadequate mixing can allow microclots. EDTA carryover can produce a markedly increased potassium with a markedly decreased calcium. Separator-gel effects on drugs and other measurands depend on tube composition, contact time, and method.

Venous collection follows the laboratory's procedure: confirm the order and preparation, identify the patient, select and clean the site, allow antiseptic to dry, collect in the required sequence, release the tourniquet as flow begins, mix additive tubes, label at the bedside, and document the collector and time. Fist pumping and tourniquet use longer than one minute increase preanalytic variation.^{44 Simundic AM, et al. Joint EFLM-COLABIOCLI recommendation for venous blood sampling. 2018.}

Special collections require their own validated instructions. A line draw controls infusion contamination and dead space. An arterial blood-gas specimen controls air exposure, anticoagulant, mixing, temperature, and time to analysis. Capillary collection controls puncture site and depth, warming, first-drop handling, and tissue-fluid contamination. How cerebrospinal fluid is divided among tubes and transported depends on the tests requested and the local tube-routing policy. Urine timing, preservation, and acceptability are covered in Specimen Handling and Acceptability and Urine Specimen Types.

Analytic and postanalytic safeguards

The analytic phase begins only after the specimen has met acceptance criteria. Reagent identity, preparation, storage, and expiration; calibration status; quality-control results; maintenance; instrument flags; and validated interference rules must support release. Under the general CLIA minimum for quantitative testing, the laboratory tests at least two control materials of different concentrations each day it performs patient testing. An individualized quality control plan, a specialty requirement, or a more stringent manufacturer instruction can replace that default with its own design. Run controls also after the reagent, calibration, maintenance, and critical-part events the procedure specifies, and release patient results only after the control results are acceptable.^{1717 Centers for Medicare & Medicaid Services. 42 CFR §§493.1105, 493.1241, 493.1242, 493.1256, and 493.1291. 2026.}

Postanalytic review checks whether the result fits the specimen, method, patient history, reference interval, and laboratory release rules. A delta check compares the current value with a prior value using analyte- and patient-specific thresholds established by the laboratory. Autoverification applies validated rules for flags, quality control, range, interference, and consistency before releasing a result without manual review.

Critical-result communication follows the laboratory's written policy. Under 42 CFR §493.1291(g), the laboratory immediately alerts the person or entity requesting the test and, when applicable, the person responsible for using the result when a result indicates an imminently life-threatening condition or a panic or alert value. CMS interpretive guidance says the record should include the date, time, result, and person notified.^{3,173 Centers for Medicare & Medicaid Services. State Operations Manual, Appendix C. 2026.17 Centers for Medicare & Medicaid Services. 42 CFR §§493.1105, 493.1241, 493.1242, 493.1256, and 493.1291. 2026.}

Corrected reports follow a separate requirement. Under 42 CFR §493.1291(k), when the laboratory detects an error in a reported patient result, it promptly notifies the authorized person who ordered the test and, when applicable, the person using the result; promptly issues a corrected report; and maintains both the original and corrected reports. How long records are kept depends on the document type and on any longer state or accreditation requirement.^{3,173 Centers for Medicare & Medicaid Services. State Operations Manual, Appendix C. 2026.17 Centers for Medicare & Medicaid Services. 42 CFR §§493.1105, 493.1241, 493.1242, 493.1256, and 493.1291. 2026.}

Pretest probability and result interpretation

Sensitivity and specificity describe performance against a reference classification. Pretest probability describes the estimated probability of the condition before the new result. Bayes reasoning combines these quantities to estimate probability after testing.^{2323 Altman DG, et al. Diagnostic tests 1. 1994.}

Probability of disease after a positive result = (sensitivity × pretest probability) ÷ [(sensitivity × pretest probability) + ((1 − specificity) × (1 − pretest probability))]

Probability of no disease after a negative result = (specificity × (1 − pretest probability)) ÷ [(specificity × (1 − pretest probability)) + ((1 − sensitivity) × pretest probability)]

• After a positive result: (0.92 × 0.10) ÷ [(0.92 × 0.10) + (0.04 × 0.90)] = 0.092 ÷ 0.128 = 71.9% probability of disease.
• After a negative result: (0.96 × 0.90) ÷ [(0.96 × 0.90) + (0.08 × 0.10)] = 0.864 ÷ 0.872 = 99.1% probability of no disease.

The same test result gives a different posttest probability when the pretest probability changes. Before you apply a performance claim, check the population, setting, patient selection, specimen quality, and reference classification behind it.

Practice