Study guide · concept · Phlebotomy
Order of draw for the CCMA: venous and capillary
The venous order of draw is blood culture, light blue, red, gold SST, green, lavender, then gray. Capillary sticks follow a different order, with lavender EDTA moved to the front of the additive tubes.
- tubes in the venous order
- 7
- blood to citrate in light blue
- 9:1
- phlebotomy items of 150 scored
- 12
§01
One reason behind every slot
Memorize the reason first. The colors follow from it.
The order of draw exists because of additive carryover. A trace of one tube's additive can ride the needle into the next tube and change that tube's result, so each tube is drawn ahead of the additives that would spoil it. Once you know what each additive does, you don't need a color mnemonic.
Phlebotomy is 12 of the 150 scored items on the 2022 test plan. Order-of-draw items come in three forms: which tube goes where, which tube follows which, and which result goes wrong when the order slips. The rest of the domain is on the phlebotomy study page.
§02
Venous order of draw (CLSI)
Seven slots. If a tube color is unfamiliar, place it by its additive.
| # | Tube | Additive | Typical tests | Handling note |
|---|---|---|---|---|
| 1 | Blood culture bottle (yellow SPS) | SPS | Blood culture | Sterile collection |
| 2 | Light blue | Sodium citrate 3.2% | PT/INR, PTT | Fill to the line; 9:1 blood to citrate |
| 3 | Red | None or clot activator | Serum chemistry, serology | Let it clot before spinning |
| 4 | Gold / SST | Clot activator + gel | CMP, chemistry | Gel separates serum after centrifuging |
| 5 | Green | Heparin | Plasma chemistry | Invert gently to mix |
| 6 | Lavender / purple | K-EDTA | CBC, hematology | Whole blood; invert gently |
| 7 | Gray | Sodium fluoride / potassium oxalate | Glucose | Fluoride keeps the glucose from falling |
§03
Capillary order is different
Same additives, different priorities.
1st
Blood gas
Collected before anything else when it's ordered.
2nd
Lavender EDTA
First among the additive microtubes.
3rd
Other additive tubes
Heparin, fluoride and the rest.
Last
Serum (no additive)
It's supposed to clot anyway.
§04
Light blue is the fussy tube
If it's underfilled, the clotting time it reports isn't real.
The light blue tube holds a measured amount of citrate for a 9:1 ratio of blood to citrate, so it has to be filled to the line. An underfilled tube has too much citrate for the blood in it and reports a falsely prolonged PT/PTT. Invert it gently 3 to 4 times. Shaking it hemolyzes the sample, and the lab may reject a hemolyzed specimen.
§05
Before you pick an answer
Four checks, about ten seconds.
- Venous or capillary? Decide before you read the options.
- Translate each color or test in the options into its additive.
- Ask which tube would be harmed by the one drawn just before it. That tube has to come earlier.
- Check that the answer keeps the groups in the right order: coag, then serum, then plasma and whole blood.
§06
Order-of-draw questions
8 questions. Pick an answer to see why it is right or wrong.
Name the additive in every tube before you choose; most of these turn on what one additive does to the next tube.
In the order of draw, the lavender (EDTA) tube is filled after the gold SST and green tubes. What is the main reason?
Answer & explanation
Answer: C. EDTA carryover alters potassium and calcium
K2-EDTA contains potassium and binds calcium, so if it is carried into a chemistry tube it falsely raises potassium and lowers calcium; drawing lavender after the SST and green tubes prevents this. Heparin is an anticoagulant, so its carryover would not clot the EDTA tube. Tube order is set by additive carryover, not by fill volume or test urgency.
- Heparin prevents clotting, so heparin carryover could never cause the lavender tube to clot.
- Tube volume does not set the order of draw; preventing additive carryover does.
- Correct: potassium EDTA carried forward falsely raises potassium and lowers calcium in chemistry tubes.
- Test urgency does not decide the order of draw; additive contamination does.
In the CLSI order of draw, which tube is collected first?
Answer & explanation
Answer: C. Blood culture (sterile) bottle
Blood cultures are drawn first to keep them sterile and prevent false positives, before the light-blue coagulation tube. Gray and lavender tubes come near the end of the order.
- Light-blue citrate tubes come second, right after blood cultures, when both are ordered.
- Lavender EDTA tubes come late in the order because EDTA can contaminate chemistry tubes.
- Correct: blood culture bottles are drawn first to keep the sample sterile and free of additive contamination.
- Gray fluoride tubes are drawn last, since their additives can affect other tests.
Why is the light-blue coagulation tube filled before the green heparin tube?
Answer & explanation
Answer: D. Heparin carryover would prolong clotting times
Heparin is an anticoagulant, so even a trace carried into the citrate tube falsely prolongs PT and PTT; that is why light blue comes before green. Citrate is also an anticoagulant, so its carryover cannot clot the heparin tube. The order of draw is based on additive carryover, not tube volume or urgency.
- Volume does not set the order of draw; additive carryover does.
- Citrate is an anticoagulant, so its carryover would not clot a heparin tube.
- Urgency does not determine order of draw; preventing additive carryover is the reason.
- Correct: heparin carried into the light-blue tube would falsely prolong PT and PTT, so citrate goes first.
When collecting blood cultures with a butterfly set, which bottle should the MA fill first?
Answer & explanation
Answer: A. The aerobic bottle
With a butterfly, the air in the tubing enters the first bottle filled, so the aerobic bottle goes first and the anaerobic bottle stays air-free. The anaerobic bottle is filled first only with a syringe, which has no tubing air, and that exception is why candidates choose it. Bottle order is set by oxygen exposure, not by labeling, and no Y-adapter splits the draw.
- Correct: with a butterfly, tubing air goes into the first bottle, so the aerobic bottle should be the one to take it.
- Label order does not decide this; what matters is which bottle can safely take the air sitting in the tubing.
- Anaerobic first is the syringe rule, where no tubing air exists; carrying it over to a butterfly is the usual slip.
- No Y-adapter step exists in blood-culture collection; the bottles are filled one at a time in a set order.
A provider orders a blood culture, a PT/INR, a CMP in a gold SST, and a CBC. In which order should the MA fill the tubes?
Answer & explanation
Answer: D. Blood culture, light blue, SST, lavender
CLSI order of draw is blood culture (sterile, first), then light blue citrate, then serum tubes (red, gold SST), then heparin, EDTA, and gray. Drawing the SST before the light blue carries clot activator into the citrate tube and distorts PT/INR. Putting lavender early carries EDTA forward, which falsely lowers calcium and raises potassium on the CMP.
- Drawing the SST before light blue lets clot activator carry into the citrate tube and distort the PT/INR.
- Blood cultures always come first to protect sterility, so light blue cannot lead here.
- Lavender this early carries EDTA into the coag and chemistry tubes, skewing calcium, potassium and clotting results.
- Correct: blood culture, light-blue citrate, serum SST, then lavender EDTA follows the CLSI order exactly.
A patient needs only a PT/INR, and the MA is using a straight needle. What does current CLSI guidance say about a discard tube?
Answer & explanation
Answer: C. No discard tube is needed
Current CLSI guidance says a routine PT/INR or PTT can be collected as the first tube with a straight needle, without a discard tube. A discard tube is still needed with a butterfly set, where tubing air would underfill the citrate tube. A lavender discard would carry EDTA into the coag tube, and drawing a red tube first is an outdated habit, not a requirement.
- EDTA in a discard tube drawn first could carry into the citrate tube and falsely affect coagulation results.
- Drawing two light-blue tubes and discarding one wastes blood; current CLSI guidance does not require it with a straight needle.
- Correct: with a straight needle, CLSI allows the light-blue tube first without a discard; a butterfly still needs one.
- A red discard tube first is an older habit, not a current CLSI requirement for straight-needle draws.
During an infant heel stick, the MA must collect a capillary blood gas, a lavender EDTA microtube, and a gold serum microtube. In what order should they be collected?
Answer & explanation
Answer: C. Capillary blood gas, lavender EDTA, gold serum
Skin-puncture order differs from the venous order: blood gas first, then the EDTA microtube, then other additive tubes, and serum last. The tempting choice copies the venous habit of filling the gold tube before lavender, but capillary blood starts clotting at once, so the EDTA specimen cannot wait behind the serum tube.
- The blood gas comes first; delaying it lets air and clotting change the gas values.
- Serum is collected last in a skin puncture, not first.
- Correct: blood gas, then EDTA, then serum is the capillary order.
- This is the venous habit (serum before EDTA) applied to a capillary draw.
In a fingerstick collection, why is the lavender EDTA microtube filled before the other additive and serum microtubes, unlike the venous order of draw?
Answer & explanation
Answer: A. Capillary blood clots fast, and platelets clump if EDTA is delayed
Blood from a skin puncture begins clotting almost immediately, so the EDTA (hematology) specimen is collected first among additives to keep platelet and cell counts accurate. The order is set by clotting speed, not by tube volume or test urgency. The first drop is wiped away because tissue fluid dilutes the sample, so it never helps a CBC.
- Correct: early clotting causes platelet clumps and falsely low counts.
- Microtube volume does not decide the order of collection.
- Test urgency does not set the order of draw; clotting speed does.
- The first drop is wiped away because tissue fluid dilutes the specimen.
That is the whole set. Open any card to re-read its explanation, or start over.
§07
After the tubes are filled
Specimen handling has its own traps.
A serum tube needs about 30 minutes to clot fully before it goes in the centrifuge. Specimen handling is part of the point-of-care testing and lab domain, and quality-control rules for waived tests are on the CLIA-waived tests and QC page. For quick recall of tube colors, use the CCMA flashcards.