Learn where most lab errors happen and the criteria a lab uses to accept or reject a specimen.
Why it matters
A laboratory result is only as good as the specimen it came from. The total testing process has three phases:
- Pre-analytical: everything before the analyser: the order, patient identification, collection, labelling, transport, receipt and processing.
- Analytical: the measurement itself, controlled by calibration and quality control (QC).
- Post-analytical: review, reporting, critical-value calls and interpretation by the care team.
Studies of laboratory error consistently find that most mistakes happen in the pre-analytical phase, often quoted as roughly 60 to 70 percent. Analysers are tightly controlled; people carrying tubes through a busy hospital are not. That is why the specimen-receipt bench has written rejection criteria, and why a medical laboratory scientist (MLS) must be able to spot a bad specimen in seconds.
Safety and scope. This lesson is awareness-level knowledge. Collecting, handling and testing patient specimens is done only in an accredited training program or an employer laboratory, under supervision, after bloodborne-pathogen training (see OSHA bloodborne pathogens, checked on 2026-10-23). Nothing here is medical advice.
The core idea: is this specimen fit for the test?
Every test has requirements written in the lab's procedure manual: tube type and additive, minimum volume, time limits, temperature, and light protection. At receipt, the specimen is checked against those requirements. If it fails, it is rejected and a new collection is requested. Testing a bad specimen does not save time; it produces a wrong answer that someone may act on.
Common rejection criteria:
- Identification problems: unlabelled tube, label that does not match the requisition, fewer than two patient identifiers, illegible or handwritten-over label.
- Wrong container: a potassium request in a potassium-EDTA (lavender) tube, or a coagulation test in anything other than sodium citrate (light blue).
- Under-filled citrate tube: coagulation tests need the blood-to-anticoagulant ratio of about 9:1. A short draw has too much citrate and falsely prolongs clotting times.
- Clotted anticoagulated specimen: clots in an EDTA tube consume platelets and cells, so a CBC is unreliable.
- Quantity not sufficient (QNS): too little sample for the test and any repeat.
- Hemolysis: red cells broke open during or after collection, releasing potassium, LDH, AST and hemoglobin into the plasma.
- Lipemia and icterus: fat or bilirubin in the sample can interfere optically. Many analysers report HIL indices (hemolysis, icterus, lipemia) so the lab can apply objective cut-offs per test.
- Time and temperature failures: a specimen that should have been centrifuged or chilled within a set time, but was not. For example, cells in an unspun tube keep consuming glucose, so glucose falls the longer it sits; ammonia specimens usually need to be on ice and tested quickly.
- IV contamination: blood drawn above an infusion line can be diluted with saline or dextrose, giving impossible combinations (very high glucose with low everything else).
- Expired tubes: the vacuum and additive are no longer guaranteed.
Worked example: the receipt bench at 07:10
Five specimens arrive in one bag. Here is how an MLS would reason about each (fictional patients):
| Specimen | Observation | Decision |
|---|---|---|
| Lavender tube, CBC | Two identifiers, correct, mixed, no clots | Accept |
| Light-blue tube, PT/INR | Filled to about half the fill line | Reject: under-filled; request recollection |
| Gold (serum gel) tube, potassium | Plasma visibly red; analyser hemolysis index high | Reject or report with a comment, per policy; potassium is falsely raised |
| Gold tube, lipid panel | Label has name only, no date of birth or record number | Reject: only one identifier |
| Lavender tube, CBC | Label name differs from requisition | Reject: mislabelled; never "fix" the label |
Notice the last row. Relabelling a mislabelled tube is one of the most dangerous things a lab can do, because the blood inside may belong to someone else. Most labs allow an exception only for irreplaceable specimens (for example spinal fluid or tissue), and then only with a documented process in which the collector comes to the lab, verifies identity and signs. The policy decides; you do not improvise.
What rejection looks like in practice
- Record the problem in the laboratory information system (LIS) with a standard rejection code.
- Notify the collecting unit so the specimen can be redrawn quickly.
- Keep the rejected specimen for the time your policy requires, in case questions come up.
- Track rejection rates as a quality indicator. A unit with many hemolyzed samples may need retraining on collection technique or tube handling.
Sometimes a sample is borderline, for example mild hemolysis for a test that is not affected. The lab procedure says which tests are affected at which index level. A good habit is to ask, "Would I trust this number if it were my family member's?" and then follow the written criteria.
Common mistakes
- Assuming "the analyser will flag it." Many pre-analytical problems, such as a mislabelled tube, cannot be detected by any instrument.
- Testing an under-filled citrate tube "because the patient is hard to draw." The result will be wrong.
- Reporting a hemolyzed potassium without a comment, which can trigger an unnecessary treatment.
- Fixing a label yourself instead of following the relabelling policy.
Quick recap
- Most lab errors are pre-analytical, so specimen acceptance is a core MLS skill.
- Check identification, container, volume, clotting, hemolysis/lipemia/icterus, and time and temperature.
- Reject with a documented code, notify the unit, and never relabel outside policy.
- Standards such as those from CLSI and the US CLIA regulations shape these rules (checked on 2026-10-23); your lab's procedure manual is the version you follow.
Try it
Open the Do tab and work through the quiz: each question is a specimen that just arrived at your bench.