6.1 Specimen Suitability for Add-on Requests
Key Takeaways
- An add-on test uses an existing specimen only when the tube type, remaining volume, analyte stability, and time since collection all match laboratory policy
- Opened or aliquoted samples increase contamination and evaporation risk—many labs restrict add-ons to unopened primary tubes when possible
- Heparin plasma and serum are not interchangeable; confirm the ordered assay’s validated matrix before adding chemistry tests
- If suitability fails for any critical factor, do not force the add-on—request recollection and document the reason in the LIS
- Always verify patient identifiers, accession linkage, and order completeness before releasing an add-on to processing or the analyzer
6.1 Specimen Suitability for Add-on Requests
Quick Answer: Add a test to an existing specimen only when tube/matrix matches the assay, enough residual volume remains, the analyte is still stable for the time and storage conditions since collection, and lab policy allows use of that container (often preferring an unopened primary tube). If any check fails, recollect and document the reason in the LIS—never “force” an unsuitable add-on.
Add-on requests (also called add-on tests, add-ons, or reflex/add orders depending on workflow) ask the laboratory to perform additional testing on a specimen already collected for other work. For the MLA, add-ons are a core Domain II skill: Specimen Preparation and Processing is the largest ASCP MLA content area, and incorrect add-on decisions cause wrong results, delayed care, and unnecessary needlesticks.
Add-ons feel efficient—no new draw—but efficiency is worthless if the sample no longer represents the patient’s status at the clinically intended time or no longer meets the assay’s validated requirements.
What an Add-on Is (and Is Not)
| Concept | Meaning for the MLA |
|---|---|
| Add-on | New order attached to a specimen already in the lab |
| Same accession / same draw | Preferred when policy allows linking to the original collection event |
| Reflex test | Protocol-driven follow-up (e.g., pathologist or instrument algorithm)—not the same as a clinician free-text add-on, but still needs a suitable specimen |
| Recollection | New collection when the existing sample cannot support the request |
The MLA does not decide medical necessity. The MLA does decide (or escalate when policy is unclear) whether the physical specimen can support the ordered test.
Suitability Checklist Before You Add
Work through these checks every time. Policy language differs by laboratory, but the logic is stable across sites.
1. Correct patient and correct specimen
- Confirm two identifiers on the tube match the order and LIS accession.
- Confirm the tube is the one intended (not a same-name neighbor in the rack).
- Confirm the specimen type is what the test requires (blood vs urine vs other fluid).
Never add a test because “the name looks right.” Wrong-patient add-ons are catastrophic reportable errors.
2. Correct tube type and matrix
Tests are validated for a matrix: whole blood, plasma, or serum, and for a specific additive.
| Request type | Common acceptable sources | High-risk mismatches |
|---|---|---|
| CBC / hematology indices | EDTA whole blood (lavender) | Serum or clotted EDTA |
| PT/INR, aPTT | Full-draw citrate plasma (light blue) | Underfilled citrate; heparin contamination |
| Many routine chemistries | Serum (gold/red) or heparin plasma (green) per method | Assuming serum and heparin are always interchangeable |
| Glucose (preservation) | Gray fluoride or method-approved serum/plasma within stability window | Old unpreserved sample with delayed separation when policy requires fluoride |
| Type and screen / blood bank | EDTA pink or lavender per blood-bank policy | Wrong additive; unlabeled or relabeled tubes |
Heparin vs serum availability is a classic add-on trap. A green-top lithium heparin tube may support a STAT chemistry panel on your analyzer, while another assay on the menu may require serum only. If only an SST remains and the assay is plasma-only (or the reverse), the add-on is not suitable even if volume looks adequate.
3. Remaining volume (QNS risk)
“Looks like enough” is not a volume check.
- Know minimum volumes for the add-on test plus residual needs for pending original tests and possible repeats.
- Account for dead volume in analyzers and aliquot tubes.
- If original testing is incomplete, do not drain the primary tube for a low-priority add-on that would jeopardize STAT or critical pending work—follow prioritization policy and escalate.
QNS after the fact wastes instrument time and may force a redraw anyway. When residual volume is borderline, escalate rather than guessing.
4. Analyte stability and time since collection
Stability is analyte-specific, not specimen-wide. A tube that is fine for a stable analyte may be invalid for a labile one.
Factors that change suitability over time:
- Hours (or minutes) since collection
- Whether cells were separated (serum/plasma off cells)
- Storage temperature (room temp, refrigerated, frozen)
- Light exposure for light-sensitive analytes
- Additive effectiveness over time (e.g., glycolysis in unpreserved samples)
Examples of stability thinking (always use your lab’s published limits):
| Situation | Suitability concern |
|---|---|
| Chemistry add-on 30 hours after draw, sample still on cells at room temperature | Many analytes drift; often exceeds max hold time |
| Potassium on an old unseparated sample | Pseudohyperkalemia risk from cell leakage |
| Ammonia, lactate, some blood-gas–related analytes | Very short stability; often not add-on candidates from routine leftover tubes |
| Bilirubin / porphyrins / some vitamins | Light degradation if not protected |
| Coagulation testing beyond validated citrate stability window | Reject or recollect per coagulation policy |
If collection time is missing or unreliable in the LIS, do not assume the specimen is still valid—investigate or recollect per policy.
5. Opened, aliquoted, or previously processed sample
Policy often prefers add-ons from an unopened primary tube because:
- Lower contamination risk
- Better chain of identity (label still on original container)
- Less evaporation and concentration artifact
- Clearer audit trail for which material was used
Opened primary tubes may still be acceptable for some tests within a short window if volume and stability allow, but many laboratories restrict sensitive assays.
Aliquots raise extra questions:
- Was the aliquot labeled with full identifiers and accession?
- Was it poured with clean technique (no pipette carried from another patient)?
- Has it been stored under validated conditions?
- Is the aliquot matrix still correct (e.g., not a diluted wash residual)?
If the only residual material is a questionable aliquot, the safe path is often recollection or supervisor review—not silent use.
6. Prior testing that consumed or altered the sample
Some workflows change the specimen:
- Centrifugation and gel separation
- Freezing and thawing
- Addition of preservatives for referral
- Microbiology setup from a shared container
- Hemolysis introduced during prior handling
An add-on that requires an unspun whole-blood specimen cannot use spun plasma leftover. A test that is invalid after freeze-thaw cannot use a previously frozen aliquot.
When Recollection Is Required
Recollect (or refuse the add-on on the existing specimen) when any of the following apply under lab policy:
- Wrong tube/matrix for the ordered test
- Insufficient residual volume for the add-on plus necessary originals/repeats
- Exceeded stability for the analyte (time, temperature, light, separation)
- Compromised integrity: hemolysis, clotting in anticoagulated tubes, contamination, leakage, or improper storage
- Identity/labeling uncertainty
- Opened/aliquoted specimen not approved for that assay
- Special chain-of-custody or legal specimen rules that prohibit non-protocol use of residual material
- Blood bank / special protocol requirements that demand a new properly labeled specimen
Do not “run it anyway and flag it” unless a licensed professional and written policy explicitly authorize that path. The MLA’s default when suitability fails is stop, recollect or escalate, document.
Verify Before Adding: Workflow Discipline
A practical MLA sequence:
- Read the add-on order completely (test name, priority, special instructions).
- Locate the candidate specimen(s) in storage or processing.
- Match identifiers on tube, LIS, and order.
- Confirm tube type/matrix against the test directory or LIS rules.
- Check collection date/time and storage history.
- Assess residual volume and pending work on the same tube.
- Inspect for hemolysis, clots, lipemia, icterus, or leakage as applicable.
- If suitable, complete LIS steps that attach the test to the correct accession/specimen ID.
- If not suitable, cancel/reject the add-on path per policy, request recollection, and notify per protocol.
When two candidate tubes exist (for example, both SST and heparin), choose the one that matches the assay’s validated matrix and has adequate volume and stability—not merely the fullest tube.
Documentation in the LIS
Add-on decisions must be traceable. Typical documentation elements include:
| Element | Why it matters |
|---|---|
| Who requested the add-on and when | Order authenticity and timing of clinical need |
| Which specimen/accession was used | Prevents testing the wrong leftover tube |
| Suitability determination | Shows policy was applied |
| Reason for rejection/recollection | Protects patient safety and supports quality review |
| Notification to nurse/provider when recollect is needed | Closes the communication loop |
| Storage location retrieval notes | Supports retrieval audits |
If your LIS requires a suitability comment, cancel code, or recollection order linkage, complete those fields accurately. Incomplete documentation makes it look as if an unsuitable sample was used—or forces another technologist to repeat your investigation.
Clinical Scenarios (MLA Exam Style)
Scenario A — Chemistry add-on, green top available
A provider adds a basic metabolic panel to a specimen drawn 45 minutes ago. An unopened lithium heparin tube remains, volume is adequate, and the lab’s chemistry methods accept heparin plasma. After identifier and stability checks, the add-on is usually appropriate.
Scenario B — Coagulation add-on, old blue top
A PT is requested on a citrate tube drawn many hours earlier and stored beyond the lab’s validated window. Even if volume remains, stability fails—recollect.
Scenario C — Only opened SST left
Sensitive or contamination-prone testing is ordered; policy requires an unopened primary when available, and none remains. Escalate or recollect rather than using a questionable open tube.
Scenario D — Volume competition
A STAT CBC is still pending on a lavender tube with low residual volume when a non-urgent add-on arrives. Protect the STAT testing; do not empty the tube for a convenience add-on.
Connection to Later Processing Topics
Key Takeaways
- Add-ons require identity + matrix + volume + stability + integrity + policy—all of them.
- Heparin plasma ≠ serum unless the assay and policy say so.
- Prefer unopened primary tubes; treat opened/aliquoted material cautiously.
- When suitability fails, recollect and document in the LIS; never force the test.
- Protect pending critical work on limited residual volume.
A provider requests a chemistry panel add-on. The only remaining specimen is an unopened lithium heparin (green) tube with adequate volume, collected 40 minutes ago and refrigerated per protocol. The lab’s chemistry method is validated for heparin plasma. What is the most appropriate MLA action?
Which factor most strongly supports rejecting an add-on request even when residual volume in the original tube looks sufficient?
Why do many laboratory policies prefer add-on testing from an unopened primary tube rather than from a previously poured aliquot?
An add-on coagulation test is requested. The only citrate tube is underfilled and was drawn several hours earlier. What should the MLA do?