How should patient posture and collection time be controlled to minimize postural effects on certain analytes?

• A. Collect samples at any convenient time without standardization.
• B. Standardize posture but ignore time of collection.
• C. Standardize patient posture during collection (sitting or lying) and collect samples at consistent times when required; document posture and time in the record.
• D. Posture and time do not affect analytes; no documentation is needed.

Answer: (C)

Posture and time of collection influence concentrations of many analytes; controlling these factors minimizes pre-analytical variability. When a patient changes position, plasma volume shifts can cause hemoconcentration or dilution, subtly altering test results for certain substances. Collecting samples at consistent times also matters because some analytes vary with circadian rhythms or with fasting status. By standardizing whether the patient is sitting or lying during collection and by drawing samples at the same times when required, you reduce variability and improve comparability of results. Documenting the patient’s posture and the collection time in the record ensures that anyone reviewing the results can interpret them correctly and compare them to prior measurements or reference ranges.