Overview
Patient preparation encompasses controllable pre-collection conditions, fasting, timing, posture, exercise, and medication status, that alter measured chemistry analyte concentrations independent of disease.
Classification
| Variable | Typical chemistry concern | Action |
|---|---|---|
| Fasting | Lipids, glucose | Confirm hours per SOP |
| Timing | TDM, diurnal analytes | Confirm window |
| Posture/exercise | Proteins, selected metabolites | Document context |
| IV/medications | Contamination or pharmacologic effect | Follow draw policy |
Morphologic Features
Preanalytical reference, morphologic cell identification is hematology, not clinical chemistry specimen handling.
Laboratory Characteristics
- Checked at order review and bedside before draw
- Exceptions require documentation for interpretation
- Not corrected by analyzer QC
Reference Intervals
Numeric HIL cutoffs, clotting times, centrifuge settings, and stability windows are method- and institution-specific. Verify against local SOP and package inserts, do not treat textbook examples as universal critical limits.
| Concept | Meaning | Notes |
|---|---|---|
| Institutional threshold | SOP/method-defined acceptability limit | Verify locally |
| H / L / I index | Hemolysis / lipemia / icterus interference flags | Assay-specific |
| Stability window | Time/temperature for valid analysis | Analyte- and matrix-specific |
Clinical and Laboratory Significance
Preparation mismatches produce false disease patterns, especially lipids, glucose, and timed drug levels.
Differential Considerations
Distinguish true metabolic disease from non-fasting or mistimed collection before escalating clinical concern.
Comparison Tables
Prepared vs unprepared chemistry draws
| Feature | Prepared collection | Unprepared collection |
|---|---|---|
| Interpretability | Matches intended clinical question | May mislead |
| Documentation | Prep status clear | Often missing |
| Action if failed | N/A | Reschedule/document/escalate |
Classification Frameworks
WHO disease classifications are not the primary framework for preanalytical chemistry specimen terminology.
Laboratory Notes
- Never invent universal fasting-hour cutoffs, verify institutional definitions
- Coordinate with nursing for inpatient fasting holds
References
Authoritative textbooks, guidelines, and reviews supporting this reference entry. Verify reference intervals, critical limits, and reflex criteria against institutional protocols and current guideline editions.
Textbooks
- Rifai N, Horvath AR, Wittwer CT, eds. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 8th ed. Elsevier; 2022.
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Elsevier; 2021.
- Bishop ML, Fody EP, Schoeff LE. Clinical Chemistry: Principles, Techniques, and Correlations. 9th ed. Jones & Bartlett; 2022.
CLSI and Professional Guidelines
- Clinical and Laboratory Standards Institute. Collection of Diagnostic Venous Blood Specimens. CLSI standard GP41. CLSI.
- Clinical and Laboratory Standards Institute. Defining, Establishing, and Verifying Reference Intervals in the Clinical Laboratory; Approved Standard. CLSI document EP28-A3c. CLSI; 2010.
Frequently Asked Questions
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