Specimen Collection

Many chemistry results are only interpretable if the patient prepared correctly, so the technologist has to turn a test requirement into instructions an ordinary person can follow. That covers how long to fast, whether water and regular medications are permitted, timing relative to a drug dose or to waking, and the mechanics of a timed urine collection — which void to discard, where the container is kept, and what to do if one is missed. Give the instruction in plain language, back it up in writing where the laboratory has a handout, and confirm the patient can repeat it back before they leave.

Not every requisition that reaches the bench should be run. The technologist screens for orders that duplicate a recent result inside the minimum retest interval, for assays that have been retired in favour of a better marker, for tests the laboratory does not perform on that specimen type, and for requests that cannot answer the clinical question being asked. The response is rarely a silent cancellation. Hold the request, check it against laboratory policy, and speak to the ordering clinician or the reference laboratory before either running or refusing it, then document what was agreed.

Accessioning is a deliberate comparison, not a formality. The technologist checks that the surname, given name, date of birth and health number on the tube match the requisition character for character, that the collection date and time agree, that the tube types present can support every test ordered, and that the fill volume is adequate. Any mismatch is treated as an identity failure. Never relabel a tube to make it agree with the paperwork or amend the paperwork to agree with the tube — contact the collector, arrange a fresh specimen where the discrepancy touches identity, and record the event.

Before anything is loaded, the technologist looks at the specimen itself and decides whether it can support the assay. Haemolysis, icterus and lipaemia all interfere optically and chemically; clots in an anticoagulated tube, gross underfill, the wrong anticoagulant, a broken cold chain or a transport delay all corrupt specific analytes. The judgement is analyte-specific rather than blanket — a haemolysed tube may still be fine for sodium but useless for potassium or lactate dehydrogenase. Where a result is released despite a defect, the interference must be flagged clearly on the report.

The centrifuged gel tube shown was collected from an inpatient while a parenteral nutrition infusion was running through the same arm. What should the technologist do first with this specimen?

AReport all results with a lipaemia comment addedBDiscard the tube and cancel the requested testsCRedraw from the other arm, away from the lineDDilute the serum with saline before analysis

Serum separated from a difficult venepuncture is distinctly red-tinged. Which analyte is most likely to be falsely elevated?

ASodiumBPotassiumCChlorideDBicarbonate

Some specimens may end up as evidence — workplace and roadside drug screens, blood alcohol, parentage testing, and samples taken in a suspected assault. For these, the laboratory must be able to prove that the sealed container examined at the bench is the one taken from that patient, and that nobody unaccounted for handled it in between. Tamper-evident seals, a custody form signed and dated at every transfer, secure locked storage, and restricted access are all mandatory. A broken seal, a gap in signatures, or an unwitnessed transfer breaks the chain and the specimen is no longer defensible.

The laboratory information system record is what every downstream user relies on, so accessioning has to be complete as well as fast. The technologist enters or verifies the accession number, the specimen type and site, the true collection date and time, the collector's identifier, the priority assigned, and any comment about integrity such as haemolysis or a transport delay. Collection time matters more than most fields: therapeutic drug levels, cortisol, and timed collections are uninterpretable without it. Corrections after the fact are made through the system's amendment function so the audit trail survives, never by overwriting silently.

Transport is a triage decision made under time pressure. Two things drive it: how urgently the clinician needs the answer, and how quickly the analyte degrades once it leaves the patient. Blood gases, ammonia, lactate, ionised calcium and homocysteine deteriorate within minutes and need immediate hand delivery, often chilled; critical care and emergency work outranks scheduled clinic work regardless of analyte. The technologist also has to know which specimens must never travel by pneumatic tube because agitation causes haemolysis, and must ensure cold-chain specimens actually stay cold in transit rather than merely starting that way.

Once specimens arrive together, processing order is its own decision. Some analytes have hard separation windows: whole blood left on the cells drives potassium up, glucose falls by several per cent an hour without a glycolytic inhibitor, and ACTH needs chilled centrifugation and prompt freezing, while renin is handled at room temperature because chilling cryoactivates prorenin and falsely raises the result. Others are stable for hours and can safely wait. The technologist sorts by stability rather than by arrival order, centrifuges and separates the time-critical tubes first, aliquots into the correct container, and freezes anything destined for a referral laboratory before turning to the routine workload.

Some results are analytically perfect and still wrong, because the specimen never represented the patient. Classic patterns are recognisable: a wildly high glucose with a high potassium points to a draw above a running infusion; a high potassium with a low calcium and an unmeasurable alkaline phosphatase points to EDTA carryover from tube-order error; a whole panel that shifts implausibly in hours points to a specimen drawn from the wrong patient. The technologist compares against previous results, applies delta checks, asks the collector what happened, and holds the report until the discrepancy is explained.

Two independent identifiers are the minimum, and they must be obtained actively. Ask an alert patient to state their full name and date of birth rather than offering a name for them to agree with, then check what they said against the wristband and the requisition. Bed numbers, room numbers and the name on a chart hanging at the foot of the bed are not patient identifiers. Where the patient cannot answer — unconscious, confused, an infant, or unidentified on arrival — the wristband or the assigned temporary number becomes the reference. Tubes are labelled at the bedside, never afterwards.

The technical collection carries its own set of controls. Choose a site clear of infusions, fistulas, haematoma and the side of a mastectomy; disinfect and let the skin dry fully so alcohol does not haemolyse the sample or contaminate an alcohol level. Keep the tourniquet under a minute to avoid venostasis. Follow the order of draw so additives do not carry over between tubes, invert each tube gently the specified number of times immediately after filling, and label at the bedside before leaving the patient. Sharps go straight into the container at the point of use.