🚧 Under construction — VoTechWorks is being built. A free tech program — complimentary, as our commitment to get America working.
voTechWorksGrade 13 · a vocational technology learning center, by urbanicity
newSchoolWorks.com › VoTechWorks › Health & Personal Services › Medical Assisting › Phlebotomy: Venipuncture, Capillary Collection, and Specimen Handling › Lesson 11
HLT-MEDI38-03 · Lesson 11 · 10.5 clock hours · theory

Special Collections: Blood Cultures, Timed Draws, and Chain of Custody

Objective. Students explain the procedural requirements for blood culture collection, timed specimen draws, and forensic chain-of-custody specimens, and correctly document each on the appropriate form.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed clinician in the field or by a certification or approval body. It is a study draft and may contain errors. Do not use it to make decisions about any patient or medication. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Special Collections: Blood Cultures, Timed Draws, and Chain of Custody

Most venipunctures follow a routine protocol, but some physician orders require extra steps to protect the specimen, the patient, or the legal integrity of the result. Three of the most common special collection types are blood cultures, timed draws, and chain-of-custody specimens. Each has strict procedural requirements that you must follow exactly — errors can lead to false results, patient harm, or a specimen that is legally inadmissible.

Blood Culture Collection

Blood cultures are ordered when a provider suspects bacteremia (bacteria in the bloodstream) or sepsis. Because even a small amount of skin contamination can cause a false-positive result, blood culture collection uses a more rigorous antisepsis technique and a two-site draw.

Why two sites? Collecting from two separate venipuncture sites — typically timed a short interval apart or simultaneously by two collectors — reduces the risk of interpreting a skin contaminant as a true pathogen. If the same organism grows in both sets, it is more likely a real infection. A contaminant is more likely to appear in only one set.

Skin antisepsis. Standard venipuncture uses 70% isopropyl alcohol. Blood culture prep adds a second antiseptic step: scrub the site with chlorhexidine gluconate (preferred) or povidone-iodine, following the manufacturer's contact time — usually at least 30 seconds of friction followed by the full recommended dry time. Allow the site to dry completely before needle insertion. Do not re-palpate the vein after antisepsis without using a sterile gloved finger.

Bottle tops. Wipe each blood culture bottle cap (aerobic and anaerobic) with a fresh alcohol pad and allow it to dry before inoculating.

Inoculation order. Inoculate the anaerobic bottle first when using a butterfly/winged collection set, because the tubing holds a small amount of air — injecting anaerobic first minimizes air exposure. When using a straight needle and syringe, inoculate the aerobic bottle first. Fill bottles to the manufacturer's recommended volume; under-filling is a leading cause of false-negatives.

Safety note. Never recap needles. Use a needleless transfer device when filling bottles from a syringe.

Timed Draws

Some laboratory values are meaningful only when related to a specific time — a meal, a dose of medication, or a defined interval. Collecting too early or too late produces a result that cannot be correctly interpreted and may lead to wrong treatment decisions.

Post-prandial glucose. A two-hour post-prandial glucose measures blood sugar two hours after the start of a meal. Document the time the patient began eating, then collect the blood specimen exactly two hours later. Label the tube with the patient's name, date, time of collection, and the notation "2-hr post-prandial." A collection window of a few minutes is generally accepted, but follow your facility policy.

Peak and trough drug levels. Therapeutic drug monitoring tells the provider whether a medication dose is in the effective range without reaching toxic levels.

Label each tube with the collection time and whether it is a peak or trough. A mislabeled or mistimed specimen can cause a provider to adjust a dose in the wrong direction, resulting in patient harm.

General rule: When you receive a timed draw order, confirm the exact time parameters with the ordering provider or nursing staff before drawing, and record all times precisely on both the label and the requisition.

Chain-of-Custody Specimens

Chain of custody (COC) is a documented, unbroken record showing who collected, handled, transferred, and tested a specimen. It is required for specimens that may be used as legal evidence — most commonly workplace drug screening and forensic toxicology. The purpose is to prevent tampering and to prove in court, if necessary, that the specimen belongs to the identified donor and was not altered.

Collection steps.

1. Verify the donor's identity with a government-issued photo ID.

2. Have the donor complete the required sections of the COC form before collection begins.

3. Collect the specimen (urine is most common; blood may be required for certain programs) under the conditions specified — some protocols require direct observation.

4. Check the specimen temperature and appearance immediately and document both on the form.

5. Seal the specimen container with a tamper-evident label or seal in front of the donor. The donor initials the seal.

6. Place the sealed specimen in the provided collection bag and seal the bag.

7. Complete your portion of the COC form, sign, and date it.

8. Maintain continuous custody or hand off to the next authorized person, who signs the form acknowledging receipt.

If chain of custody is broken — for example, the specimen is left unattended, the seal is missing, or a signature step is skipped — the specimen may be rejected by the laboratory and is not usable as legal evidence. The test may need to be repeated, and failure to follow COC can expose the employer, the collection site, and the phlebotomist to legal liability.

Safety and confidentiality. COC specimens are subject to privacy rules. Do not discuss the donor's results with unauthorized parties.

Key terms9

BacteremiaThe presence of bacteria in the bloodstream; the primary indication for blood culture collection.
Anaerobic bottleA blood culture bottle designed to grow bacteria that do not require oxygen; inoculated first when using a winged collection set.
Two-site blood cultureDrawing blood culture sets from two separate venipuncture sites to help distinguish a true bloodstream infection from a skin contaminant.
Post-prandialAfter a meal; a two-hour post-prandial glucose is collected exactly two hours after the patient starts eating.
Trough levelThe lowest concentration of a drug in the blood, measured immediately before the next scheduled dose.
Peak levelThe highest concentration of a drug in the blood, measured at a defined interval after a dose is administered.
Chain of custody (COC)A documented, unbroken record of every person who collected, handled, or transferred a forensic or drug-screen specimen, ensuring its legal integrity.
Tamper-evident sealA label or seal placed on a specimen container that shows visible evidence if the container has been opened; required for COC specimens.
Chlorhexidine gluconateAn antiseptic agent used as the preferred skin prep for blood culture collection because of its broad-spectrum and residual antimicrobial activity.

Worked examples3

1. A patient's lunch tray arrived at 11:45 AM. The physician ordered a two-hour post-prandial glucose. At what time should you collect the blood specimen, and what should the label show?
  1. Step 1: Identify the start time of the meal — 11:45 AM.
  2. Step 2: Add two hours: 11:45 AM + 2:00 = 1:45 PM.
  3. Step 3: Plan to collect the specimen at 1:45 PM.
  4. Step 4: Label the tube with the patient's full name, date of birth, date, time of collection (1:45 PM), collector's initials, and the notation '2-hr post-prandial glucose. Meal started 11:45 AM.'
Answer: Collect at 1:45 PM. The label must include the patient ID, collection time (1:45 PM), and the designation '2-hr post-prandial; meal start 11:45 AM.'
2. A patient is receiving a medication by IV. The nurse documents that the dose finished infusing at 8:00 AM. The physician orders a peak level to be drawn 30 minutes after the infusion ends and a trough level drawn immediately before the next dose, scheduled at 2:00 PM. When should each specimen be collected and how should each label be marked?
  1. Step 1: Calculate the peak draw time: 8:00 AM + 30 minutes = 8:30 AM.
  2. Step 2: The peak tube is collected at 8:30 AM and labeled 'Peak — collected 8:30 AM, 30 min post-infusion.'
  3. Step 3: The trough is drawn immediately before the next dose at 2:00 PM — collect just before 2:00 PM (e.g., 1:55 PM per facility policy).
  4. Step 4: The trough tube is labeled 'Trough — collected [time], pre-dose 2:00 PM.' Include patient name, date of birth, date, and collector initials on both labels.
Answer: Peak: collect at 8:30 AM, label 'Peak, 8:30 AM.' Trough: collect immediately before the 2:00 PM dose, label 'Trough, [collection time], pre-dose.' Both labels must include full patient identification and collector initials.
3. You are collecting blood cultures using a butterfly set. You have one aerobic and one anaerobic bottle. In what order do you inoculate the bottles, and why?
  1. Step 1: With a butterfly (winged) set, the tubing contains a small volume of air.
  2. Step 2: Inoculate the anaerobic bottle first to minimize the amount of air introduced into it, preserving the anaerobic environment.
  3. Step 3: Inoculate the aerobic bottle second — any residual air in the tubing is acceptable in the aerobic bottle.
  4. Step 4: Fill each bottle to the manufacturer's recommended volume mark to avoid under-filling (a cause of false-negative results).
Answer: Anaerobic bottle first, then aerobic. This order minimizes air exposure to the anaerobic bottle when using a winged collection set.
In class: Compare blood culture collection technique to standard venipuncture using a side-by-side procedure comparison chart; students identify the three main differences (two-site collection rationale, skin antisepsis steps using chlorhexidine or iodine, inoculation order) and present their chart findings to the class. · Work through two timed-draw case studies: a two-hour post-prandial glucose and a peak/trough therapeutic drug level; students calculate collection times, draft specimen labels with correct time stamps, and explain why the timing window matters for result validity. · Examine a chain-of-custody form used for workplace drug screening; students fill out the form using a fictional scenario, seal and initial the specimen bag correctly, and explain verbally what happens legally if chain of custody is broken.
Materials: Blood culture bottle set (aerobic and anaerobic), chlorhexidine skin antisepsis swabs, chain-of-custody form (forensic/drug screen type), timed-draw case study handouts, phlebotomy textbook chapter on special collections
Check: Students complete a written scenario quiz covering blood culture site rationale, timed-draw calculation for a given order, and chain-of-custody sealing steps; 80% or higher required to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Phlebotomy — Specimen Collection Procedures
1. When collecting blood cultures using a butterfly needle set, which bottle should be inoculated first?
Phlebotomy — Specimen Collection Procedures
2. Why are blood cultures drawn from two separate venipuncture sites rather than one?
Phlebotomy — Timed Specimens
3. A patient's lunch started at 12:15 PM. The provider orders a two-hour post-prandial glucose. At what time should the phlebotomist collect the specimen?
Phlebotomy — Timed Specimens
4. A trough drug level is best described as the drug concentration measured:
Phlebotomy — Infection Control and Safety
5. Which antiseptic is preferred for skin preparation before blood culture collection?
Phlebotomy — Chain of Custody
6. During a chain-of-custody urine drug screen collection, after you seal the specimen bag, what must happen next to maintain legal integrity?
Phlebotomy — Chain of Custody
7. What is the consequence if chain of custody is broken for a workplace drug-screen specimen?
Phlebotomy — Specimen Collection Procedures
8. A phlebotomist using a syringe (not a butterfly set) to collect blood cultures should inoculate the bottles in which order?
Record this lesson on my transcript. Sign in with your key and enrollment email to record lessons (enroll free if you have no key). This page stays open to read and practise.
← Previous lessonProgram planNext lesson →