Specimen Processing for the NHA CPT: Centrifuging, Temperature, Light and Chain of Custody

A specimen can be collected perfectly and still be ruined in the next hour. That's what the NHA CPT's Processing domain tests: 14 scored items on nine tasks (5A to 5I) in NHA's test plan, from centrifuging and aliquoting to temperature, light and time, chain of custody, research shipments, the lab information system, critical values and re-collection. Handling rules are set test by test in each lab's catalog, so this guide uses published lab and manufacturer rules as examples and flags where they differ.

Clotting and centrifuging NHA CPT specimens (task 5A)

Serum tubes are left to clot before they are spun, and published times differ by tube and by lab:

Quest's chart gives 10 to 15 minutes of spinning for its tubes. If an exam question asks how long a gold SST should clot, 30 minutes is the answer that fits most sources: Quest gives it for the SST, and ADLM's tube selection pearl says complete clotting typically takes 30 minutes, which is why the 5-minute RST exists. Michigan Medicine's 10 minutes is a local minimum. At work, use your lab's times and the centrifuge settings it specifies. With 14 items on nine tasks, planned NHA CPT practice includes 182 Processing questions at launch.

How long serum and plasma can stay on the cells

Some results drift if serum or plasma sits on the cells too long. ADLM's pearl explains why: the cells keep consuming glucose, so glucose reads falsely low, and once glucose runs out potassium leaks out of the cells and reads falsely high. Its guidance is that whole blood should ideally be processed within 2 hours of collection when serum or plasma is needed.

Labs set their own limits. Michigan Medicine's guidelines say specimens for potassium or glucose must be separated from the red cells within 4 hours, and MLabs asks client sites to centrifuge or deliver those samples within 3 hours and to note the collection date and time on the requisition. For the exam, 2 hours is the safer answer when a question asks how soon serum or plasma should come off the cells; a lab's longer limit is a local exception, not the general rule. Other limits are test-specific:

• Ethanol: WakeMed lists red cells not separated within 2 hours as a cause for rejection.
• Coagulation whole blood: Michigan Medicine wants it in its coagulation lab within 3 hours at room temperature (45 minutes for anti-Xa assays; up to 23 hours for a prothrombin time), or prepared as frozen platelet-poor plasma.
• Capillary EDTA: BD says specimens can be stored in its Microtainer EDTA tubes for up to four hours at room temperature before hematology testing.

The pattern to remember: collection time goes on the requisition, and the clock starts at the draw, not when the specimen reaches processing.

Aliquoting without ruining the specimen (k88)

Aliquoting means transferring serum or plasma into a separate labeled tube. Michigan Medicine's rules give the details a question can turn on:

• Use the right vial. Its test entries say to aliquot into a plastic tube, and its coagulation guidelines specify polypropylene (cloudy plastic), not polystyrene (clear hard plastic).
• Avoid the buffy coat when pipetting coagulation plasma off the cells.
• One aliquot per test when several frozen coagulation tests are ordered.
• Label the transfer tube. Quest's chart shows the transport vial labeled with the specimen type and patient ID.

OSHA's bloodborne pathogens standard applies at the processing bench too: procedures with blood must minimize splashing, spraying, spattering and droplets, and mouth pipetting is prohibited.

Specimens that go on ice, stay warm or get frozen (task 5B)

The test plan's examples for task 5A, "freezing or refrigeration," and for 5B, "temperature, light, or time," are exactly these decisions.

Protecting specimens from light

Michigan Medicine's guidelines explain that light exposure can alter several kinds of results, and that specimens are exposed whenever the refrigerator or freezer door opens and during handling and transport. Its rule: blood specimens that need light protection go in a brown paper bag or are wrapped in foil (preferred), and urine goes in a brown container, a brown bag or foil (preferred). Its list includes total and fractionated bilirubin, carotene, porphyrins and porphobilinogen, and several vitamins, among them B1, B2, B3 (niacin), C and K1. Its total bilirubin entry repeats the instruction: protect the specimen from light. For the exam, bilirubin is the classic example. For quick recall of these handling rules, the 63 Processing flashcards planned for full NHA CPT prep are sorted with the rest of this domain.

Packaging and transport, from the courier bag to Category B (task 5D)

Four layers of rules apply, from the bench to an aircraft:

• OSHA, every specimen. Blood specimens go in containers that prevent leakage during collection, handling, processing, storage and transport. Containers leaving the facility must carry the biohazard label or color coding. If the outside of the primary container is contaminated, it goes in a second leak-proof container, and if the specimen could puncture the primary container, the second one must be puncture-resistant.
• WHO, at the collection site. Pack samples in a leak-proof plastic bag with an outside compartment for the request form, so the paperwork stays clean, and use a rack or padded holder for multiple tubes.
• Michigan Medicine, by courier. A leak-proof primary receptacle goes into a sealed, leak-proof secondary transport bag with a biohazard sign, the requisition goes in the bag's separate pocket, and the bag's "Room Temperature," "Refrigerated" or "Frozen" designation tells the courier how to handle it.
• DOT, by shipper. 49 CFR 173.199 requires Category B infectious substances to travel in triple packaging: a primary receptacle, secondary packaging and a rigid outer packaging, with cushioning so leaks don't compromise it. The outer package carries a diamond-shaped mark with the proper shipping name "Biological substances, Category B" next to it, and the name and telephone number of a knowledgeable person must appear on a document such as the air waybill, or on the package.

Michigan Medicine adds that air shipments also follow IATA and ICAO rules and that anyone who packages specimens for transport must be trained to do it. Task 5D's examples, "obtain correct specimen bag, air waybill, and packaging," come straight from this layer. Research protocols set their own tube processing and kits on top of these rules.

Chain of custody on the NHA CPT (task 5C)

Task 5C's examples are forensic studies and blood alcohol. The clearest legal definition is DOT's, in 49 CFR 40.3: chain of custody is "the procedure used to document the handling of the urine specimen from the time the employee gives the specimen to the collector until the specimen is destroyed," using the federal custody and control form. NHA's test plan applies the same idea to forensic specimens and blood alcohol; the form and the steps come from the agency or facility procedure that requires them.

Labs mark the difference between legal and medical collections. WakeMed allows alcohol pads for "non-legal or non chain of custody" ethanol collections only, and Children's Minnesota labels its medical ethanol test "not for legal purposes." The DOT urine collection steps, including the dated, initialed tamper-evident seals, are in the NHA CPT special collections guide.

Data, critical values and re-collection (tasks 5E to 5I)

The last tasks in the domain are about information:

• Written procedures. CLIA's 42 CFR 493.1242 requires labs to have written policies for patient preparation, specimen collection, labeling (name or unique identifier, and source when appropriate), storage and preservation, transport, processing, and acceptability and rejection, and to record the date and time each specimen arrives.
• Critical values. Under 42 CFR 493.1291(g), the lab must immediately alert the person who ordered the test when a result indicates an imminently life-threatening condition, or panic or alert values. Michigan Medicine's critical value policy, for example, has the lab telephone the client as soon as such a result is verified. Task 5G applies this to point-of-care and CLIA-waived tests, which you may run yourself.
• Results to the record. Task 5H asks you to make sure results reach the ordering provider and that the medical record is updated.
• Re-collection. Task 5I covers contacting the patient when a specimen can't be tested. Published rejection reasons include insufficient volume and hemolysis (WakeMed), mislabeled or unlabeled specimens (Children's Minnesota), and coagulation specimens not collected and transported properly (Michigan Medicine).

Three Passy examples on processing

These are original Passy practice items, not NHA questions.

Example 1: an ammonia level

A lavender tube for an ammonia level has just been drawn on an outpatient. What should happen next?

• A. Place it on ice at once and get it processed quickly
• B. Keep it at room temperature until the courier arrives
• C. Freeze the whole-blood tube right away for transport
• D. Open the stopper so the specimen can cool down faster

Answer: A. Michigan Medicine's entry says to place it on ice immediately and get it to the lab within 15 minutes, or centrifuge and freeze the plasma within 30. Ammonia rises at room temperature (B), whole blood must not be frozen (C), and the stopper stays on until aliquoting (D).

Example 2: cold agglutinins

Which handling is correct for a cold agglutinin specimen?

• A. Collect a pre-warmed red tube and keep it at 37 °C
• B. Collect a gold SST and refrigerate it until spun
• C. Collect a red tube and place it on crushed ice
• D. Collect a lavender tube and freeze the whole blood

Answer: A. Michigan Medicine requires a pre-warmed red tube kept at 37 °C until the serum is separated, and lists an SST or a specimen refrigerated before separation as unacceptable.

Example 3: a bilirubin in a sunny room

A total bilirubin is drawn at a bedside next to a bright window, and the courier is 30 minutes away. What protects the result?

• A. Wrapping the tube in foil or putting it in a brown bag
• B. Placing the tube on ice until the courier arrives
• C. Inverting the tube a few more times every ten minutes
• D. Leaving the tube on the windowsill so it stays warm

Answer: A. Michigan Medicine lists bilirubin among specimens that must be protected from light and prefers foil. Ice (B) and extra mixing (C) don't address light, and D does the opposite.

The reasoning matters more than the specimen list, and planned explanations name the handling rule behind each NHA CPT processing answer, right or wrong.

Your next step for NHA CPT processing questions

Sort the specimens in this guide into four columns (ice, warm, light, time limit) and say the reason for each. Then see how the tube additives behind these rules work in the NHA CPT tube colors and additives guide, and try the 20 free NHA phlebotomy practice questions.