Quality Assessment
Preanalytic, Analytic, and Postanalytic Quality Assessment
Every laboratory result carries the effects of patient physiology, specimen collection and handling, the measurement system, and result reporting. Locating a discrepancy within the testing cycle directs the investigation toward the records and corrective actions most likely to explain it.1,2
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.
| Phase | Boundary | Representative failures | First evidence to review |
|---|---|---|---|
| Preanalytic | Test selection and ordering through specimen arrival and preparation for analysis | Wrong patient or test, incomplete preparation, wrong container, short draw, clot, contamination, hemolysis, delayed transport, or unsuitable storage | Order, patient identifiers, collection record, container, specimen appearance, transport conditions, and receipt time |
| Analytic | The measurement procedure | Reagent deterioration, calibration error, failed quality control, instrument malfunction, pipetting error, or method-specific interference | Quality-control and calibration records, reagent lot and expiration, maintenance, flags, interference indices, and instrument messages |
| Postanalytic | Result verification through delivery to the ordering clinician | Transcription or interface error, unsuitable reference interval, missed critical-result notification, uninvestigated delta, or incorrect corrected report | Result history, reference interval, autoverification rules, notification record, corrected-report record, and audit trail |
A defect can cross phase boundaries. Prolonged contact with cells begins as a handling problem and changes the specimen before analysis. Hemolysis begins during collection or transport and produces an analyte-dependent effect during measurement. The investigation follows the event from its origin through the reported result.
Patient preparation and biologic variation
Patient state can change a measured concentration even when the collection and method perform correctly. The order and collection instructions should name the preparation that affects interpretation.3,4
| Variable | Laboratory consequence | Control |
|---|---|---|
| Time of day | Cortisol, iron, therapeutic drugs, and other measurands can vary with circadian rhythm or dosing time. | Collect at the defined time and record it when interpretation depends on timing. |
| Food and fasting | Meals can change glucose and triglycerides and can make the specimen lipemic. | Apply the test-specific fasting instruction and document preparation. |
| Posture and tourniquet use | Standing and prolonged venous stasis concentrate proteins, protein-bound substances, and cells. Fist pumping and prolonged stasis can change several measurands. | Standardize posture when required, allow about 15 minutes of rest after a recent posture change, avoid fist pumping, and release the tourniquet as blood flow begins. |
| Exercise and stress | Recent exertion or acute stress can change lactate, creatine kinase, leukocytes, catecholamines, and related results. | Record relevant exertion or stress and delay elective collection when the procedure specifies a rest period. |
| Medication and supplement use | A drug may change the patient’s physiology, react in the measurement procedure, or create a recognizable assay artifact. | Record relevant exposure and use the current assay instructions during investigation. |
| Peak and trough timing | Drug concentration changes across the dosing interval. | A trough is collected immediately before the next dose. The drug and the laboratory procedure determine when a peak is collected. |
Bed rest and intravenous fluid can lower measured concentrations of cells and proteins through hemodilution. Age changes alkaline phosphatase, creatinine, bilirubin, and hematologic intervals. Tobacco exposure can raise carboxyhemoglobin, hemoglobin, red-cell count, and leukocyte count. These variables guide preparation and interpretation, but the reporting laboratory’s validated interval is still the comparison point for an individual result.3
Hormone therapy can shift some sex-associated laboratory results. Current ADLM guidance recommends analyte-specific interpretation that considers the hormone regimen and duration, organ inventory, muscle mass, and the laboratory’s validated reporting policy. After at least 6 months of stable gender-affirming hormone therapy, hemoglobin, hematocrit, and red-cell results generally follow the interval associated with the affirmed gender. Creatinine and estimated glomerular filtration rate require additional care because muscle mass and the sex input used by the calculation can alter the estimate, and ADLM reports no consensus for that input. Dual calculation or cystatin C may help when kidney assessment remains uncertain.5
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 visible specimen change therefore cannot support one correction factor across methods.2,6
| Finding | Main mechanisms | Laboratory response |
|---|---|---|
| Hemolysis | Red-cell contents enter plasma or serum; free hemoglobin adds spectral and chemical effects; intracellular fluid can dilute extracellular constituents. Potassium, lactate dehydrogenase, aspartate aminotransferase, phosphate, and other measurands may change. | Use the analyzer’s hemolysis index and the laboratory’s analyte-specific interference limits. Suppress, qualify, repeat, or request recollection according to the validated policy and clinical urgency. |
| Icterus | Bilirubin absorbs light and can participate in chemical reactions. | Apply the method’s icterus index and manufacturer interference claim. Use a validated blank, wavelength correction, alternate method, or recollection pathway when appropriate. |
| Lipemia | Turbidity scatters light; a reduced plasma-water fraction can affect methods that dilute the sample. | Apply the method’s lipemia index. A validated ultracentrifugation, dilution, blank, or alternate method may resolve the effect. |
| Clot or microclot | Inadequate mixing or unsuitable anticoagulation allows fibrin formation. | Reject or process only under a test-specific validated procedure. Inspect analyzer flags and probes when a clot is discovered after aspiration. |
| Infusion contamination | Fluid or medication from a vascular line dilutes or adds constituents to the specimen. | Review the collection site and infusion, then recollect from an acceptable site or follow the validated line-draw procedure. |
Collection-related hemolysis can follow a needle or device that produces excessive shear, forceful syringe aspiration or transfer, vigorous mixing, collection before antiseptic dries, or unsuitable transport. Match the device to the vein and required flow, allow antiseptic to dry, fill tubes through the closed collection system when available, mix by gentle inversion, and use validated transport conditions.4
Pseudohyperkalemia and pseudohypokalemia. In vitro red-cell injury, fragile leukemic cells, extreme thrombocytosis, or delayed separation can raise measured potassium without a matching increase in the patient’s circulating plasma. Marked metabolically active leukocytosis can consume potassium after collection and lower the measured result. Compare serum and plasma when appropriate, review the blood count and collection history, and repeat promptly with a properly collected and handled specimen. The size of the artifact cannot be predicted reliably from visual hemolysis alone.7
Pseudohyponatremia. Severe hyperlipidemia or hyperproteinemia reduces the water fraction of plasma. An indirect ion-selective electrode dilutes the specimen and can report a falsely low sodium concentration under these conditions. A direct ion-selective electrode measures undiluted specimen and generally avoids this electrolyte-exclusion artifact. Measured osmolality and the clinical setting help identify the discrepancy.8
Assay-specific examples
| Interferent | Pattern | Investigation |
|---|---|---|
| Excess biotin | Some streptavidin-biotin sandwich immunoassays produce falsely low results; some competitive assays produce falsely high results. Direction and magnitude follow the assay design. | Review supplements, dose, renal function, collection time, package insert, and laboratory policy. Use a validated alternate method or recollect after the assay-specific interval. |
| Heterophile or human anti-animal antibodies | Antibody bridging or blocking can produce a falsely high or low immunoassay result. | Compare with the clinical pattern and prior results. Serial dilution, blocking reagent, an alternate platform, or reference-laboratory testing may help during the investigation. |
| Anti-CD38 therapy | Daratumumab and isatuximab can cause panreactivity during indirect antiglobulin testing and can mask an alloantibody. | Notify the transfusion service and follow its Blood Banking procedure. |
| Emicizumab | Activated partial thromboplastin time-based factor VIII and inhibitor assays can give misleading results during therapy, and the effect may persist for up to 6 months after the last dose. | Use assay classes identified as suitable in the current prescribing information and the coagulation laboratory’s procedure. |
| Nucleic-acid amplification inhibitors | Heparin, heme compounds, and other matrix constituents can inhibit amplification. Poor stabilization can degrade the target, and amplified product can contaminate later reactions. | Follow the test-specific collection and stabilization instructions. Keep preamplification and postamplification work separate and use the validated contamination-control workflow. |
The FDA describes clinically important biotin interference and recommends that device developers characterize and communicate it. The current assay instructions control any withholding interval; a single universal interval cannot account for dose, kidney function, assay tolerance, and measurement design.9 A current AABB association bulletin covers anti-CD38 interference in transfusion testing, and the current emicizumab prescribing information identifies affected coagulation assays.10,11
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. Room number and physical location are excluded as identifiers.1,12
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.13
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 connect a defect with its consequence:
| Finding | Main concern | Action |
|---|---|---|
| Unlabeled specimen or identifier mismatch | Result can be assigned to the wrong patient. | Reject under the identification policy. Apply the documented irreplaceable-specimen exception only when the policy permits it and the responsible parties resolve identity. |
| Wrong container or additive | The method lacks the required matrix or receives a chemical interferent. | Reject or seek documented approval under a validated exception. |
| Underfilled citrate tube | Excess citrate relative to plasma can prolong clotting results. | Reject according to the coagulation procedure. Adjust citrate for a hematocrit above about 55% using the laboratory’s validated calculation.14 |
| Clot in anticoagulated blood | Cell counts fall and analyzer probes may obstruct; coagulation testing becomes unsuitable. | Reject the affected testing. |
| Hemolysis, icterus, or lipemia | The effect varies by analyte and method. | Apply the analyte-specific interference policy. |
| Delay or temperature excursion | Cells, enzymes, organisms, or measurands may change before analysis. | Compare the documented time and temperature with the test’s validated stability limit. |
| Leaking container | Specimen integrity and worker safety are compromised. | Contain the leak, follow the exposure procedure when needed, and request recollection under policy. |
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.15
| Sequence | Additive or specimen | Function and common use |
|---|---|---|
| 1 | Blood-culture medium | Supports recovery of microorganisms; collection technique protects volume and sterility. |
| 2 | 3.2% buffered sodium citrate | Reversibly binds calcium. A 9:1 blood-to-anticoagulant ratio supports routine coagulation testing. |
| 3 | Serum, with or without clot activator and separator gel | Produces serum after clotting. Gel and clotting requirements come from the test and tube instructions. |
| 4 | Lithium or sodium heparin | Potentiates antithrombin and limits clot formation. Commonly used for plasma chemistry. |
| 5 | K2EDTA | Chelates calcium and preserves cellular morphology. Commonly used for hematology and selected molecular tests. |
| 6 | Glycolytic inhibitor | Fluoride slows glycolysis. Prompt separation or another validated stabilizing system may still be required for glucose. |
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 the paired clue of markedly increased potassium and 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.4
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 govern the applicable design. Controls also follow reagent, calibration, maintenance, and critical-part events specified by the procedure, and acceptable control results precede patient-result release.13
Postanalytic review asks 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 and documents the result, recipient, date, and time. Under 42 CFR §493.1291(k), the laboratory promptly notifies the authorized person, issues a corrected report, and retains duplicates of the original and corrected reports. Laboratory policy documents the date, time, and person responsible for the change. How long records are kept depends on the document type and on any longer state or accreditation requirement.13
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.16
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)]
Worked example. A test has 92% sensitivity and 96% specificity in its intended setting. The pretest probability is 10%.
- 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 carries a different posttest probability when the starting probability changes. A performance claim therefore only makes sense alongside the population, setting, patient selection, specimen quality, and reference classification behind it.
References
- Clinical and Laboratory Standards Institute. Patient and Laboratory Specimen Identification Processes. 1st ed. CLSI standard PRE01. Clinical and Laboratory Standards Institute; 2024. Accessed August 28, 2026.
- Clinical and Laboratory Standards Institute. Handling, Transport, Processing, and Storage of Blood Specimens for Routine Laboratory Examinations. 1st ed. CLSI guideline PRE04. Clinical and Laboratory Standards Institute; 2023. Accessed August 28, 2026.
- Rifai N, Chiu RWK, Young I, Burnham CAD, Wittwer CT, eds. Tietz Textbook of Laboratory Medicine. 7th ed. Elsevier; 2023.
- Simundic AM, Bölenius K, Cadamuro J, et al. Joint EFLM-COLABIOCLI recommendation for venous blood sampling. Clin Chem Lab Med. 2018;56(12):2015-2038. doi:10.1515/cclm-2018-0602.
- Association for Diagnostics & Laboratory Medicine. ADLM guidance document on incorporating gender diversity in pathology and laboratory medicine. Published July 2026. Accessed August 28, 2026.
- Clinical and Laboratory Standards Institute. Interference Testing in Clinical Chemistry. 3rd ed. CLSI guideline EP07 Plus. Clinical and Laboratory Standards Institute; 2018. Reaffirmed October 2022. Accessed August 28, 2026.
- Simundic AM, Baird G, Cadamuro J, Costelloe SJ, Lippi G. Managing hemolyzed samples in clinical laboratories. Crit Rev Clin Lab Sci. 2020;57(1):1-21. doi:10.1080/10408363.2019.1664391.
- Aziz F, Sam R, Lew SQ, Massie L. Pseudohyponatremia: mechanism, diagnosis, clinical associations and management. J Clin Med. 2023;12(12):4076. doi:10.3390/jcm12124076.
- US Food and Drug Administration. Testing for Biotin Interference in In Vitro Diagnostic Devices: Guidance for Industry. October 2020. Accessed August 28, 2026.
- Association for the Advancement of Blood & Biotherapies. Mitigating the Anti-CD38 Interference with Serologic Testing. Association Bulletin #16-02. Revised March 2026. Accessed August 28, 2026.
- Genentech, Inc. Hemlibra (emicizumab-kxwh) prescribing information. Revised July 2025. Accessed August 28, 2026.
- The Joint Commission. Two patient identifiers: understanding the requirements. Updated April 21, 2026. Accessed August 28, 2026.
- Centers for Medicare & Medicaid Services. 42 CFR §§493.1105, 493.1241, 493.1242, 493.1256, and 493.1291. Electronic Code of Federal Regulations. Updated August 27, 2026. Accessed August 28, 2026.
- Clinical and Laboratory Standards Institute. Collection, Transport, and Processing of Blood Specimens for Testing Plasma-Based Coagulation Assays. 6th ed. CLSI standard H21. Clinical and Laboratory Standards Institute; 2024. Accessed August 28, 2026.
- Clinical and Laboratory Standards Institute. Collection of Diagnostic Venous Blood Specimens. 8th ed. CLSI standard PRE02. Clinical and Laboratory Standards Institute; 2025. Accessed August 28, 2026.
- Altman DG, Bland JM. Diagnostic tests 1: sensitivity and specificity. BMJ. 1994;308:1552. doi:10.1136/bmj.308.6943.1552.