Order of Draw for the NHA Phlebotomy Exam: Venipuncture, Capillary Collections and Blood Cultures

NHA's test plan names the order of draw three separate times. Task 3J asks you to follow it for venipuncture, task 3P for capillary collection, and knowledge statement k78 covers the order for blood cultures; k59 adds fill levels and inversions. The order that NHA's test plan expects you to know rests on CLSI's standards, which task 1B lists among the operational standards a phlebotomy technician follows. Passy doesn't reproduce CLSI's documents; the sequence below comes from CLSI's own public summary.

The CLSI venous order of draw for the NHA CPT

CLSI lists six groups, in this order. The closure colors are CLSI's examples; manufacturers and labs can use others.

What each additive does and which tests use each tube are covered in the NHA CPT tube colors and additives guide. This guide is about the sequence.

Why the order of draw exists: additive carryover

CLSI's reason is cross-contamination: blood samples are drawn "in a specific order to avoid cross-contamination of the sample by additives found in different collection tubes." When additive from one tube is carried into the next, it can change that tube's results. The Association for Diagnostics & Laboratory Medicine's phlebotomy and tube selection pearl gives the classic example: EDTA carried into the next tube can make that sample's calcium read falsely low and its potassium falsely high. That is why lavender comes after the serum and heparin tubes. Three rules follow from CLSI's summary:

• Tubes CLSI doesn't list go wherever their additive is least likely to alter the next tube's results if carryover happens.
• Clot activator and coagulation don't mix. CLSI says plastic serum tubes containing a clot activator may interfere with coagulation testing.
• Only three things may come before the citrate tube: blood culture tubes, glass nonadditive serum tubes, or plastic serum tubes without a clot activator.

That last rule is the one to know cold. A gold or plastic red tube with clot activator can never go before light blue. BD's points-to-practice sheet gives the same instruction in plain words: collect tubes in the order shown, top to bottom, "to prevent cross contamination of tube additives." Knowing the rule, not just the list, is what lets you handle a tube you haven't memorized, and planned explanations for NHA CPT order-of-draw questions name the CLSI rule behind the answer.

Tube holder, syringe or winged set: the same NHA CPT order

CLSI says the order is the same for specimens collected by syringe, by tube holder, or into tubes pre-evacuated at the time of collection. What changes with a syringe is how the tubes get filled:

• Use a transfer device. BD's sheet says to transfer blood from a syringe with a blood transfer device and to let each tube's vacuum draw the blood in, filling the tubes in the order of draw.
• Don't push the plunger. BD warns that pushing the plunger when transferring blood can cause hemolysis and needlestick injury, and the WHO guidelines on drawing blood say the same about extra pressure and hemolysis.
• Keep your hands away. WHO's best practice is to place the tube in a rack before filling it from a syringe or winged set, and to use one hand or a needle shield.

The discard tube when a winged set comes first

A winged (butterfly) set's tubing holds air, its "dead space." Quest Diagnostics' specimen collection tube chart gives the rule: when you use a winged set and a coagulation (citrate) tube is the first specimen tube, draw a discard tube first. The discard tube fills that dead space with blood, so the citrate tube gets the right blood-to-additive ratio, and it doesn't need to be completely filled. Quest says the discard tube should be a nonadditive or coagulation tube.

Quest's rule is tied to the winged set's tubing; it doesn't call for a discard tube when a citrate tube is drawn first with a straight needle and holder.

Labs word this differently. Michigan Medicine Laboratories' order-of-draw document (September 2022) says that when only a coagulation specimen is drawn, you draw 1–2 mL into a red top no-additive tube, discard it, and then collect the specimen; its older coagulation guideline (2019) uses another light blue tube as the discard. Either way, CLSI's rule still holds: nothing with a clot activator goes before the citrate tube. For an exam question, the answer that fits every source is a nonadditive tube or another light blue citrate tube, never a gold or plastic red tube with clot activator. At work, your facility's procedure decides which discard tube you use.

Blood cultures in the NHA CPT order of draw

Blood culture bottles are first in CLSI's order. BD's BACTEC collection instructions, written for a push-button winged set with a holder, add three points:

• Blood cultures are taken "first in an order of draw procedure before any other blood collection tube."
• With that set, select the aerobic vial first, hold the vial upright, and fill to the marked level; then fill the anaerobic vial.
• After the culture bottles, draw any other ordered tubes in the order of draw.

A set is one aerobic and one anaerobic bottle. Skin preparation, fill volumes and the number of sets are in the NHA CPT special collections guide.

Where tubes CLSI doesn't list fit

Your lab's procedure places the other tubes, using CLSI's carryover principle. Two examples show how much local orders can add:

• Michigan Medicine Laboratories (2022) follows the CLSI groups and slots in its own tubes: Myco/F culture bottle and isolator tube after the routine culture bottles, royal blue trace-element serum tubes after the serum tubes, royal blue EDTA with the EDTA tubes, yellow ACD tubes after gray, and QuantiFERON tubes last. It mixes all tubes by inverting them 6 to 8 times.
• WHO's 2010 guidelines show an illustrative ten-tube table based on a 2003 U.S. consensus, with a nonadditive tube second, before the citrate tube, and an ACD tube between EDTA and oxalate/fluoride. WHO tells users to verify colors and order with their local laboratory.

For the exam, CLSI's six groups are the safe answer, because NHA's test plan points to CLSI standards. At work, your lab's posted order wins.

The capillary order of draw runs the other way

Task 3P and knowledge statement k72 cover the order for capillary (skin puncture) collections, and it is not the venous order. Two sources agree:

• WHO: with skin punctures, collect the hematology specimen first, then chemistry, then blood bank specimens. WHO says this is "essential to minimize the effects of platelet clumping," that it is the reverse of the venipuncture order, and that if more than two specimens are needed, venipuncture may give more accurate results.
• BD: its Microtainer tube page, citing CLSI's 2008 capillary collection standard (H4-A6), gives the order as EDTA tubes, then other additive tubes, then serum tubes.

So for a fingerstick or heelstick: lavender EDTA first, then additive microtubes such as heparin, then serum. Capillary technique itself, including site and depth, is in the venipuncture and dermal puncture guide. For quick daily recall of both orders, the 126 Routine Blood Collections flashcards planned for NHA CPT prep cover this domain at launch.

A memory aid for the NHA CPT venous order

This one is Passy's own. For Culture, Citrate, Serum, Heparin, EDTA, Fluoride:

"Can Cats Swim? Hardly Ever, Frankly."

Then add two reminders: "nothing with clot activator before light blue," and "capillary starts with EDTA." If a mnemonic doesn't stick, AI Rescue, planned under every NHA CPT explanation, can offer a different memory trick at launch.

Three Passy examples on the order of draw

These are original Passy practice items, not NHA questions.

Example 1: a six-tube venipuncture

Orders call for blood cultures, a light blue citrate tube, a gold serum separator tube, a light green lithium heparin tube, a lavender EDTA tube and a gray fluoride tube. Which sequence follows CLSI's order of draw?

• A. Cultures, light blue, gold, light green, lavender, gray
• B. Cultures, gold, light blue, light green, lavender, gray
• C. Light blue, cultures, gold, lavender, light green, gray
• D. Cultures, light blue, light green, gold, gray, lavender

Answer: A. CLSI's order is culture, citrate, serum, heparin, EDTA, fluoride. B puts a gold tube, which has a clot activator, before the citrate tube. C puts citrate before the cultures and EDTA before heparin. D puts heparin before serum and gray before lavender.

Example 2: three microtubes from a heelstick

An infant's heelstick is collected into a lavender EDTA microtube, a lithium heparin microtube and a serum microtube. In what order should they be filled?

• A. Serum, lithium heparin, lavender EDTA
• B. Lavender EDTA, lithium heparin, serum
• C. Lithium heparin, serum, lavender EDTA
• D. Lavender EDTA, serum, lithium heparin

Answer: B. For skin punctures, BD (citing CLSI's capillary standard) gives EDTA first, other additive tubes next and serum last, and WHO puts hematology specimens first. A and C follow venous habits; D puts serum ahead of an additive tube.

Example 3: a citrate tube through a winged set

Only a light blue citrate tube is ordered, and the phlebotomist is using a winged collection set with a tube holder. What should she do before filling the citrate tube?

• A. Draw a nonadditive discard tube to fill the set's tubing
• B. Draw a gold serum tube first so the citrate tube fills faster
• C. Underfill the citrate tube to allow for air in the tubing
• D. Fill the citrate tube first and let the vacuum clear the air

Answer: A. Quest's chart says a discard tube should be drawn first in exactly this case, to fill the tubing's dead space and keep the blood-to-additive ratio right. B breaks CLSI's rule against clot activator before citrate. C and D leave the citrate tube short of its correct ratio, and BD says fill volume is especially critical for light blue tubes.

Reworking these sequences until they're automatic is the point of review, and planned Fix It review brings back every order-of-draw question you miss until the reasoning sticks.

Your next step for NHA order-of-draw questions

Write the six CLSI groups from memory, then add the capillary order underneath and the discard-tube rule beside light blue. Check yourself against the 20 free NHA phlebotomy practice questions, and if sequences keep tripping you up, the guide to what makes the NHA phlebotomy exam hard explains why near-misses cost points.