Work like a medical laboratory scientist: accept or reject specimens, read chemistry, hematology, microbiology and blood bank results, call critical values, run daily QC and plan your certification.

Clinical Laboratory Practice

## Why it matters

A laboratory result is only as good as the specimen it came from. The **total testing process** has three phases:

1. **Pre-analytical:** everything before the analyser: the order, patient identification, collection, labelling, transport, receipt and processing.
2. **Analytical:** the measurement itself, controlled by calibration and quality control (QC).
3. **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](https://www.osha.gov/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

1. Record the problem in the laboratory information system (LIS) with a standard rejection code.
2. Notify the collecting unit so the specimen can be redrawn quickly.
3. Keep the rejected specimen for the time your policy requires, in case questions come up.
4. 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](https://clsi.org/) and the US [CLIA regulations](https://www.cms.gov/medicare/quality/clinical-laboratory-improvement-amendments) 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.


Learn where most lab errors happen and the criteria a lab uses to accept or reject a specimen.

Pre-analytical phase

Pre-Analytical Errors Explained | Total Testing Process Part 2

## Why it matters

Blood collection tubes contain different **additives**: anticoagulants, clot activators, gels and preservatives. When several tubes are filled from one needle, a tiny amount of additive can be carried from one tube into the next. If EDTA from a lavender tube gets into a chemistry tube, it binds calcium and adds potassium, so the report may show a dangerously high potassium and a low calcium that the patient does not really have. The **order of draw** exists to prevent that carry-over.

> **Safety and scope.** Venipuncture is a clinical skill learned in an accredited phlebotomy, MLT or MLS program and practiced only under supervision on consenting patients, after bloodborne-pathogen and sharps training. Never practice on yourself or anyone else at home. This lesson is knowledge only; nothing here is medical advice.

## The core idea: the standard order

The order below follows the CLSI collection standard used by most US labs (always check your own lab's procedure, which is the version you follow):

| Order | Typical cap color | Additive | Common uses |
|---|---|---|---|
| 1 | Blood culture bottles | Culture medium | Blood cultures (drawn first to stay sterile) |
| 2 | Light blue | Sodium citrate | Coagulation (PT/INR, aPTT) |
| 3 | Red or gold | None, or clot activator with or without gel | Serum chemistry, serology |
| 4 | Green | Heparin (lithium or sodium) | Plasma chemistry |
| 5 | Lavender or pink | EDTA | CBC, HbA1c, blood bank |
| 6 | Grey | Sodium fluoride / potassium oxalate | Glucose, lactate |

Cap colors are conventions and can vary by manufacturer and country, so the **label on the tube** (the additive name) is what counts.

## Why this order works

- **Cultures first**, because sterility matters most and nothing should touch the needle before them.
- **Citrate early**, because coagulation tests are sensitive to clot activators and to tissue factor. If a butterfly set is used and citrate is the first tube, a **discard tube** is drawn first to fill the tubing's dead space, so the citrate tube still fills to the correct 9:1 ratio.
- **Serum tubes before plasma tubes**, so clot activator is not carried into anticoagulated tubes.
- **EDTA and fluoride/oxalate last**, because their contamination does the most damage: EDTA (as potassium EDTA) raises potassium and binds calcium and magnesium; oxalate and fluoride also bind calcium and inhibit enzymes.

## Handling after the draw

Order is only half the job. Each tube must also be:

- **Filled correctly.** Vacuum tubes are designed to draw the right volume for the additive.
- **Inverted gently** the number of times the manufacturer specifies (often 3 to 4 for citrate and 5 to 10 for others). Shaking causes hemolysis; not mixing lets anticoagulated tubes clot.
- **Labelled at the patient's side** immediately after collection (see the next lesson).
- **Transported** within the time and temperature limits for each test.

## Worked example: planning a draw

A requisition (fictional) asks for blood cultures, PT/INR, a basic metabolic panel in a gold tube, a CBC and a glucose in a grey tube. Using a butterfly set, the plan is:

1. Blood culture bottles (aerobic, then anaerobic, per the manufacturer).
2. Light blue (citrate). A discard tube is not needed here, because the culture bottles already filled the tubing; if cultures were not ordered, a discard tube would be drawn first.
3. Gold (serum, clot activator and gel).
4. Lavender (EDTA).
5. Grey (fluoride/oxalate).

If the lab later sees a potassium of 9.5 mmol/L with a calcium near zero in the gold tube (a combination incompatible with life in a patient who is talking), EDTA contamination is the first suspect. The lab would reject the result and request a redraw, not call it as a critical value.

## A memory aid

Many students remember the sequence as **"Stop, Light, Red, Stay Put, Green Light, Go"**: Sterile (cultures), Light blue, Red, SST (gold), Green, Lavender, Grey. Any mnemonic is fine as long as you can explain *why* each tube sits where it does; the reasons are what help you troubleshoot.

## Common mistakes

- Drawing the EDTA tube before chemistry tubes, causing false high potassium and false low calcium.
- Forgetting the discard tube when citrate is first with a butterfly set, so the citrate tube is under-filled.
- Trusting cap color instead of reading the additive on the label.
- Shaking tubes vigorously instead of gentle inversion.

## Quick recap

- Order of draw prevents additive carry-over: cultures, citrate, serum, heparin, EDTA, fluoride/oxalate.
- EDTA contamination looks like very high potassium with very low calcium.
- Fill, invert gently, label at the patient's side, and transport on time.
- Phlebotomy itself is learned and practiced only in supervised clinical training.

## Try it

Open the **Do** tab for the quiz: sequence a draw and diagnose a contaminated result.


Recall the standard order of draw, why it prevents additive carry-over, and how to handle tubes after collection.

Collection and order of draw

Order of Draw and Additives | Blood Collection

Invent a fictional patient (full name, date of birth, record number) and a test order for a urine drug screen.

On paper or in a document, draw a specimen label with two identifiers, collection date and time, collector initials, source, and a made-up accession number.

Draw a simple chain-of-custody form with columns: released by, received by, purpose, date, time, signature.

Fill in at least four transfers (collector, courier, lab receipt, storage) for your fictional specimen, including a seal-applied entry witnessed by the donor.

Now deliberately introduce three errors into a copy: for example a missing time, a room number as an identifier, and a missing signature at one transfer.

Swap with a classmate or put it aside for an hour, then audit the copy as a reviewer and list every error you find and the action your lab policy would take.

Compare your audit with the list of errors you introduced. Note any you missed.

## Why it matters

A perfect test on the wrong patient's blood is worse than no test at all. Identification errors can lead to a missed diagnosis, the wrong treatment, or, in the blood bank, a fatal transfusion reaction. Labelling and tracking are how a lab proves that **this result belongs to this patient** and that the specimen was handled correctly at every step.

> **Safety and scope.** This lesson and its activity are paper exercises with fictional patients. Real specimen collection and handling happen only in supervised clinical training or employment, after bloodborne-pathogen training. Never use real patient information for practice: it is protected health information.

## Patient identification

Before any collection, the collector confirms identity with **at least two patient identifiers**, such as full name and date of birth or medical record number. The room number is never an identifier. In hospitals, the collector compares the patient's spoken answers (when possible) and wristband with the requisition. Patient-safety goals published by accreditors such as The Joint Commission make two identifiers a baseline requirement.

## What goes on the label

Each tube is labelled **at the patient's side, immediately after collection**, never in advance. A typical label carries:

- Patient full name and a second identifier (date of birth or record number).
- Date and time of collection.
- Collector's initials or ID.
- A barcode linking to the order (the **accession number**) in the laboratory information system (LIS).
- For non-blood specimens: the **source** (for example "urine, clean catch" or "wound, left heel").

Barcoded labels printed at the bedside reduce transcription errors. The LIS records each scan, so the lab can see when a specimen was collected, received and tested.

## Tracking inside the lab

Once received, the specimen is **accessioned**: scanned in, checked against the order, and given a status. Aliquots (portions poured into secondary tubes) get their own labels that link back to the primary tube. Every move (centrifuge, analyser rack, refrigerator, send-out box) should be traceable. When something goes wrong, this trail is how the lab finds out where.

## Chain of custody

Some specimens are evidence: workplace drug tests, forensic samples, some paternity tests. For these, the lab follows a formal **chain of custody** (CoC): a documented, unbroken record of everyone who handled the specimen, from collection to final disposal. Typical features:

- A CoC form with a unique specimen ID that matches the label.
- A **tamper-evident seal** applied in front of the donor, who initials it.
- A signature, date and time for **every transfer** between people or locations.
- Secure, access-controlled storage.
- Any broken seal or gap in signatures is documented and may make the result unusable.

Environmental and food testing labs use chain of custody too, so this skill transfers across lab careers.

## Worked example: auditing a batch

You are the reviewer for four fictional labels:

| Label | Problem | Fix |
|---|---|---|
| "J. Rivera, Room 412, 07:15" | Room number is not an identifier; only one real identifier | Reject; recollect with two identifiers |
| "Jordan Rivera, 1984-03-02, MRN 55120, 07:15, AB" | None | Accept |
| "Jordan Rivera, MRN 55120" (no time or collector) | Missing time and collector | Follow policy: usually reject or contact the collector before testing |
| Urine tube with name, DOB, time, collector, no source | Source missing for a culture | Contact the unit to document the source before culture setup |

And one chain-of-custody form: the seal was applied at 09:02 by the collector, the courier signed at 09:40, and the lab signed receipt at 11:15, but no one signed for the 10:30 hand-off to the overnight fridge. That gap must be documented; depending on the program's rules, the specimen may be reported as unsuitable.

## Common mistakes

- Pre-labelling tubes before the draw (the classic route to a wrong-blood-in-tube error).
- Using room or bed numbers as identifiers.
- Leaving the source off microbiology specimens.
- Letting a courier sign "for" another person on a CoC form.

## Quick recap

- Two identifiers, confirmed with the patient, every time.
- Label at the patient's side right after collection, with time and collector.
- The LIS accession and barcode link every aliquot back to the order.
- Chain of custody is an unbroken, signed record from collection to disposal.

## Try it

Open the **Do** tab. You will design a label and a chain-of-custody record on paper and audit them for gaps.


Label and track a specimen with two identifiers, LIS accessioning and a formal chain of custody.

Chain of custody and labelling

SJH - Patient Safety: 2 Patient Identifiers

What Is a Chain of Custody and Why Does Every Sample Need One?

Accept or reject specimens, follow the order of draw, and label and track specimens with a chain of custody.