Every laboratory has a rejection log. Fewer laboratories treat it as a production metric with a root cause behind every entry. A rejection rate of three per cent sounds tolerable until you cost it out: recollection kits, courier trips back to the collection site, clinician time spent explaining the repeat, and a patient who now has to return for a second visit.
The good news is that rejection is not random. In most Canadian community laboratories and hospital collection sites, the same six failure modes account for the overwhelming majority of rejected samples. Each one has an identifiable root cause and a fix that belongs to a specific person.
What a Rejection Actually Costs Your Site
Start by pricing one rejection in your own setting. Include the consumables in the recollection kit, the staff minutes to explain the repeat to the patient, the second appointment, the courier leg, and the laboratory's own accessioning time on the discarded sample. Then multiply by the monthly rejection count. In most clinics the number is large enough to justify a project, and small enough that nobody has run the calculation.
Track the rate by collection site, by collector, and by test group rather than as a single laboratory-wide figure. A site-level view tells you where to send training; a test-level view tells you what to fix in the collection procedure.
Failure Mode 1: Volume Shortfalls and Wrong Tube Ratios
Short draws are the most common rejection in tube-based collection, and the reason is rarely stubbornness. Difficult veins, a tourniquet left on too long, or a collector who stops when the tube looks half full all produce the same result. The tube additive is calibrated to the draw volume: an under-filled citrate tube has too much anticoagulant for the plasma it holds, and an under-filled EDTA tube changes the concentration of everything measured in it.
The fix is procedural. Teach the fill line, not the tube size. Confirm the correct order of draw so additive carry-over does not contaminate the next tube, and give collectors a smaller-volume tube option for patients whose veins will not support a full draw.
Failure Mode 2: Haemolysis
Haemolysis shows up as a pink or red plasma layer, and it invalidates potassium, lactate dehydrogenase, and a long list of other analytes. The causes are mechanical: a needle that is too small for the vein, a syringe pulled too hard, blood forced through the needle into the tube, vigorous shaking instead of gentle inversion, or a sample left in a hot vehicle before pickup.
Attack it from both ends. Use the largest needle the vein will take, let the vacuum fill the tube rather than pushing it, invert by the count your tube manufacturer specifies, and get samples out of the collection room and into the transport route quickly.
Failure Mode 3: Clotted Anticoagulant Samples
A clot in an EDTA tube means the sample cannot be used for a full blood count. The usual cause is incomplete mixing, not an expired tube, although expired tubes and over-filled tubes also produce clots. Inversion counts exist for a reason and they are per tube: eight to ten gentle inversions for EDTA is typical, and the count is different for citrate and heparin tubes.
Mix immediately after the tube leaves the holder, keep the tube upright afterwards, and audit your own clot rate by collector so the retraining is targeted rather than general.
Failure Mode 4: Mislabelled and Unlabelled Containers
Mislabelling is the failure mode with the highest potential for patient harm, which is why most laboratories have a zero-tolerance rule and why accreditation reviewers probe it. Labelling at the bedside, with the patient present, and applying the label to the container rather than the lid, is the standard. Pre-labelling tubes before the patient arrives is the practice that creates the risk.
Two controls work: physically separate the unlabelled tube rack from the labelled one, and make the label process part of the draw sequence rather than a task for afterwards. Barcode label stock also matters; a label that falls off in refrigeration is functionally an unlabelled sample.
Failure Mode 5: The Wrong Container for the Test
Wrong-container rejections cluster around a handful of tests: samples for trace element work collected in a standard tube, viral transport medium substituted for bacterial culture medium, a first-morning urine collected in a cup when the assay needs a preserved 24-hour jug. The root cause is usually a test menu that has grown faster than the collection instructions have been updated.
Keep one current collection manual, in the collection room, that maps every test on your menu to a container, a volume, transport temperature, and stability window. Review the sheet whenever the menu changes. Deal with superseded collection kits rather than storing them beside the current ones.
Failure Mode 6: Temperature and Time Out of Range
Samples that leave the site on time and arrive warm, or frozen when they should have been cool, are rejected for instability rather than for any visible defect. The failure can be a courier delay, an unconditioned gel pack, a bag placed against the wall of a summer vehicle, or a sample set aside while the collector finishes paperwork.
| Failure mode | Usual root cause | Fix | Owner |
|---|---|---|---|
| Volume shortfall | Fill line not taught; no small-volume tubes | Teach fill lines and order of draw; stock alternative tubes | Collection lead |
| Haemolysis | Needle size, syringe pull, shaking | Needle selection guidance; inversion training | Collection lead |
| Clotting | Incomplete mixing | Per-tube inversion counts; clot rate audit | Collection lead |
| Mislabelling | Pre-labelled tubes; labels that fall off | Label at the patient; barcode stock qualification | Quality manager |
| Wrong container | Outdated collection instructions | Single current manual; pull superseded kits | Quality manager |
| Temperature excursion | Unconditioned packs; transit delay | Packing routine with a temperature log | Transport lead |
Making the Numbers Move
Pick one failure mode, measure it for a month by site, change one thing, and measure again. Rejection rates respond to procedure changes far more reliably than to reminder emails. A collection site that labels at the patient, teaches fill lines, and packs to a written routine will see its rejection log shrink, and the reduction shows up as recovered staff time rather than as a line item anyone notices.
The consumables side of the fix is smaller than the procedural side, but it is not zero. A leak-proof graduated specimen cup and a 95 kPa transport bag remove two failure modes from the list before the collector even starts. Sites that also run sterilizers can request a biological indicator trial pack separately.
Related Reading
- Specimen shipping and packaging rules for Canadian laboratories
- Laboratory biohazard waste: bags and disposal
- Earlier in this series: specimen collection containers for Canadian laboratories
- Next in this series: pediatric specimen collection
- Browse clinic supplies for collection-room consumables
Frequently Asked Questions
What is an acceptable sample rejection rate?
There is no single number that applies to every setting, and published benchmarks vary widely by test mix and patient population. The useful approach is to establish your own baseline by collection site and by test group, then work on the failure modes that account for most of your rejections. A falling trend on the same measure is more informative than a comparison against another laboratory.
Why does an under-filled tube get rejected when the blood looks normal?
Because the additive inside the tube was measured for a full draw. In a citrate tube the anticoagulant-to-blood ratio is what keeps the sample liquid, and in an EDTA tube the additive concentration affects the measurement itself. The sample may look fine and still deliver a result that cannot be trusted, which is why fill lines are part of the collection procedure.
Can we stop haemolysis by switching to a smaller needle?
A smaller needle often causes it. Shear forces rise as the needle bore narrows, particularly if the vacuum is strong or the vein is fragile. For most adult draws the better move is the largest needle the vein supports, letting the tube fill from the vacuum, and avoiding any transfer between syringe and tube.
How should rejected samples be documented?
Record the sample identifier, the test requested, the rejection reason, the collector and site, and the action taken. Aggregated by failure mode, that record becomes your improvement plan. It also gives you the evidence an assessor expects when the laboratory's pre-examination process is reviewed.
Do specimen transport bags prevent temperature excursions?
No. A transport bag is a containment device: it protects staff and other samples from leaks and carries paperwork in a separate pocket. Temperature control comes from packaging design, conditioned gel packs or dry ice, and the route itself. Use both, and log the temperature when your procedure requires it.
Last updated: September 2026. CliniEco Medical is a licensed medical device establishment (MDEL #35334, Importer, Class I).
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