Four specimens, four decisions

You are covering the blood gas bench. Four specimens arrive in sequence, each with one defect. Under a supplied local policy, decide whether to accept and analyze as drawn, recollect before analysis, or report with an explicit caveat describing the affected direction of change. This decision requires naming the defect, predicting which measured values it pushes and in which direction, and choosing the bounded action the policy allows, not just recognizing that something is wrong.

Specimen 1 arrives with a visible 0.3 mL air bubble still mixed into the blood; it was never expelled. Specimen 2 was drawn correctly but sat on the counter for 45 minutes before anyone noticed it, outside the laboratory's validated syringe/specimen/analyzer window. Specimen 3 was drawn into a syringe with excess liquid heparin rather than the standard dry, electrolyte-balanced syringe, leaving visibly diluted blood. Specimen 4 was drawn from an arterial line without discarding the flush volume first, so it is contaminated with heparinized saline.

For each specimen, identify the defect, state its expected direction where known (or that it is unpredictable), and apply the laboratory's clear local recollection rule: recollect when a specimen defect makes the result unsuitable for its intended use or when local acceptance criteria are not met. A caveated report is used only where local policy explicitly permits it.

Telling a measured PCO2 from a calculated bicarbonate is what makes this distinction usable; conflating the two leads to misjudging which number to distrust. Name the defect and its direction before you choose accept, recollect, or caveat, because the policy rule depends on that reasoning, not on the result looking abnormal.