Activated Clotting Time (ACT): Nursing Guide
Bedside activated clotting time supports high-dose unfractionated heparin monitoring during cardiopulmonary bypass, coronary angioplasty, ECMO, and selected dialysis settings — where nurses must obtain immediate whole-blood samples, follow device-specific targets, and escalate bleeding or clotting trends that do not match the clinical picture.
Contents
Quick Facts
Key Takeaway
ACT reflects how long whole blood takes to clot after an activator is added — higher seconds mean greater heparin effect.
Specimen & Collection Details
Nurse quick-reference for collection prep that affects result quality.
Device-specific cartridge or sample cup
Per analyzer instructions (not a standard central-lab vacutainer)
Whole blood (device-specific point-of-care sample)
Small whole-blood volume per device cartridge — follow manufacturer and local point-of-care protocol
After heparin bolus, at ordered intervals during the procedure, and until stabilized post-procedure per institutional protocol
No special preparation is usually required
Test immediately at point of care; sample is not stable for routine central-lab transport
Minutes at bedside
Point-of-care coagulation (operating room, cath lab, ICU, dialysis unit)
What is Activated Clotting Time (ACT)?
Activated Clotting Time (ACT) is a point-of-care coagulation test that measures how many seconds it takes whole blood to clot after an intrinsic-pathway activator (such as celite, kaolin, or glass beads) is added. It reflects the inhibitory effect of high-dose unfractionated heparin — and some direct thrombin inhibitors — on clot formation, rather than measuring heparin concentration directly.
Overview
Nurses most often encounter ACT in perioperative cardiac care, the catheterization laboratory, ECMO circuits, and selected dialysis settings where heparin doses are high enough that standard laboratory aPTT monitoring is not clinically useful or is too slow. The test must be performed immediately beside the patient because results are time-critical and the specimen is not suitable for routine transport to a central laboratory.
Because different analyzers use different activators and detection methods, ACT values are not interchangeable between devices or institutions. A result that meets target on one machine may not translate to another. Nurses support safe anticoagulation by confirming the correct protocol, documenting device and timing, communicating trends, and watching for bleeding or thrombosis even when the numeric ACT appears acceptable.
Before and during ACT monitoring, confirm the correct patient, heparin infusion or bolus plan, and institution-specific ACT target for the procedure and analyzer in use. Obtain the sample immediately at the point of care, communicate subtherapeutic or supratherapeutic trends to the perfusionist, anesthesiologist, or prescriber per protocol, and escalate active bleeding or new clotting concerns according to facility policy.
Perioperative Anticoagulation Monitoring Safety
ACT guides high-stakes anticoagulation where both clotting and bleeding can cause rapid harm. A single subtherapeutic value during bypass or ECMO may precede circuit thrombosis; supratherapeutic values with hemorrhage require urgent team response. Never equate ACT seconds across different devices or with aPTT results.
- Subtherapeutic ACT during cardiopulmonary bypass, PCI, or ECMO with circuit pressure changes or thrombosis signs
- Supratherapeutic ACT with active bleeding, falling hemoglobin, or hemodynamic instability
- Invalid or delayed sample sent to wrong analyzer while heparin decisions are pending
- Using ACT to monitor low-dose ward heparin when aPTT or anti-Xa is the ordered assay
Document: device and cartridge, sample time and site, ACT in seconds, institutional target used, heparin dose context, who was notified, and bleeding or clotting observations.
What ACT Can and Cannot Tell You
This test can help identify:
- Whether high-dose unfractionated heparin is exerting sufficient anticoagulant effect at the bedside
- Trends in anticoagulation during bypass, PCI, ECMO, and selected dialysis protocols
- When repeat sampling or heparin adjustment discussion is needed relative to institutional targets
- Response context for some direct thrombin inhibitor protocols when ACT is used per local policy
This test cannot:
- Measure actual heparin concentration or replace anti-Xa when that is the ordered assay
- Be compared directly to aPTT values or converted between different point-of-care devices
- Diagnose thrombosis or bleeding alone — clinical and circuit monitoring remain essential
- Serve as the primary monitor for routine low-dose IV heparin on general wards per reviewed references
POC Device and Line Checks Before ACT
Verify
Clarify before proceeding when:
- Order specifies aPTT or anti-Xa but team is using ACT without protocol approval
- Wrong analyzer or expired cartridge is available at bedside
- Heparin infusion rate change is undocumented or conflicting among team members
- Prior ACT invalid because of air bubble, clot, or insufficient sample volume
- ACT result conflicts with visible bleeding, circuit clotting, or pressure alarms
- Patient temperature or hemodilution changed significantly during bypass without protocol review
- Attempt is made to send ACT sample to central laboratory instead of immediate bedside testing
ACT Values With Heparin and Bleeding Context
Integrate ACT with heparin dose and timing, device-specific targets, circuit or access observations, hemoglobin trend, platelet count, temperature, and procedural phase. Serial trends on the same analyzer matter more than one isolated value.
| Clinical context | Pair with ACT trend | Nursing focus |
|---|---|---|
| CPB on bypass | ACT below target with rising line pressures | Urgent perfusionist notification; prepare for authorized heparin adjustment |
| Post-protamine reversal | ACT not shortening toward baseline | Escalate bleeding risk; surgical hemostasis and repeat coagulation assessment |
| PCI / cath lab | ACT above target with groin oozing | Access-site monitoring; communicate to cardiologist per protocol |
| ECMO maintenance | Stable ACT within target; patient stable | Continue ordered interval monitoring; still assess circuit and perfusion |
Point-of-Care ACT at the Bedside
| Bedside point | Nursing note |
|---|---|
| Same device rule | Never compare today’s Hemochron ACT to yesterday’s i-STAT ACT — trends must use one analyzer |
| Sample immediacy | Delayed cartridge insertion falsely shortens ACT; draw and run sample without interruption |
| ACT vs aPTT | Common NCLEX trap: they monitor heparin effect differently and are not interchangeable |
| Ward heparin drip | ACT is usually wrong test for standard IV heparin titration — verify aPTT order |
| Hypothermia on bypass | Cool blood may affect ACT; follow cardiac protocol rather than guessing correction factors |
| Protamine timing | Document ACT after reversal — prolonged ACT with bleeding triggers surgical escalation |
Perioperative ACT Monitoring Workflow
Diagnostic safety badge: Critical-result test — prompt review and escalation may be required during high-dose heparin procedures.
Check-before-test protocol
- Identity + procedure + correct ACT device and target
- Heparin bolus/infusion verified with perfusion or prescriber
- Point-of-care quality control current
- Sample plan aligned with protocol intervals
- Bleeding and circuit baseline documented
Critical teach-back questions
- “Can you tell me why we are checking your blood clotting time during this procedure?”
- “What access-site or bleeding changes should you report after surgery?”
- “Why might the team take several small blood samples while you are on the bypass machine?”
Care coordination: perfusionist, anesthesiologist, cardiothoracic surgery, cath-lab team, ECMO team, laboratory/point-of-care services, nephrology for dialysis, and rapid response per institutional protocol.
ACT Quick Practice Checklist
- Is this the correct monitoring test for the heparin dose and clinical setting?
- Am I using the institution-approved device and target for this procedure?
- Was the sample obtained and run immediately without pre-analytic delay?
- Does the ACT trend match circuit observations, access sites, and hemodynamics?
- Who must be notified now if ACT is out of range or invalid?
Why Activated Clotting Time (ACT) is Ordered
ACT is ordered when clinicians need rapid bedside assessment of high-dose heparin effect during procedures that require intense, short-term anticoagulation.
| Clinical Indication | What the Test Answers | Nursing Rationale |
|---|---|---|
| Cardiopulmonary bypass surgery | Is heparin anticoagulation adequate to prevent clotting in the bypass circuit? | Supports heparin bolus and infusion titration before and during bypass; ACT monitoring is commonly used in this setting per institutional cardiac surgery protocols. |
| Percutaneous coronary intervention (PCI) | Is anticoagulation sufficient during the intervention without excess bleeding risk? | Allows rapid dose adjustment in the catheterization laboratory when high-dose heparin is required and aPTT turnaround is too slow. |
| Extracorporeal membrane oxygenation (ECMO) | Is circuit anticoagulation maintained within protocol while limiting hemorrhage? | Frequent bedside monitoring supports circuit patency and bleeding surveillance in critically ill patients on extracorporeal support. |
| Hemodialysis with heparin anticoagulation | Is heparin effect adequate for the dialysis session and reversal plan? | May guide heparin dosing and protamine reversal in selected dialysis protocols — always follow local dialysis and nephrology policy. |
Contraindications and Precautions
ACT is a monitoring test rather than a standalone treatment decision. Nurses focus on situations requiring clarification before relying on the result or proceeding with anticoagulation changes.
- Wrong analyzer, expired cartridge, or incorrect sample technique — repeat per point-of-care quality protocol before dose changes.
- Active hemorrhage, hemodynamic instability, or suspected circuit clotting despite apparently therapeutic ACT — escalate clinically, not by number alone.
- Attempt to use ACT to monitor low- or moderate-dose ward heparin when institutional policy requires aPTT or anti-Xa — clarify the ordered monitoring test.
- Heparin-induced thrombocytopenia, severe thrombocytopenia, or platelet dysfunction may prolong ACT independently of heparin dose.
- Hypothermia, hemodilution, and blood temperature changes during bypass may affect ACT and device performance.
- Lupus anticoagulant and other coagulation abnormalities may complicate interpretation when ACT is used outside standard high-dose heparin settings.
- ACT below institutional target during bypass, ECMO, or PCI with signs of circuit clotting or thrombosis.
- ACT above target with active bleeding, falling hemoglobin, hemodynamic instability, or surgical site hemorrhage.
- Rapidly changing ACT trend that does not match clinical status, or inability to obtain a valid point-of-care result when anticoagulation decisions are pending.
Patient Preparation
Most ACT testing requires no fasting or special patient preparation. Preparation focuses on correct device setup, heparin orders, and point-of-care competency per institutional policy.
Pre-test checksReview unfractionated heparin infusion rate, recent boluses, protamine availability, direct thrombin inhibitors (e.g., bivalirudin when ACT is used per protocol), antiplatelet agents, and other anticoagulants. Do not independently change prescribed anticoagulation without authorization — communicate ACT trends to the responsible clinician or perfusion team.
Performance — nursing procedure guide
This page is a Tests & Diagnostics guide for Activated Clotting Time (ACT). It emphasizes why the test is ordered, how to interpret results, when to escalate, and preparation factors that affect validity — not step-by-step performance technique (those live under Nursing Procedures when available).
Step-by-step technique, supplies, infection prevention, and immediate post-procedure monitoring for this test are covered in:
Use the Patient preparation, Results and interpretation, and Nursing responsibilities sections on this page for order verification, pre-analytic checks, result follow-up, critical-value escalation, and documentation.
Result follow-up at a glance
Nursing workflow on this page — from order to safe action on results:
Results and Interpretation
ACT is reported in seconds. A higher ACT generally indicates greater anticoagulation (longer time to clot). Targets are procedure- and institution-specific; nurses apply the local protocol rather than memorizing universal thresholds.
Reference ranges, critical values, and protocols may vary by laboratory, institution, patient population, and testing method. Always follow local policy and the reporting laboratory’s reference range.
| Result | Range / Finding | Clinical Meaning | Nursing Action |
|---|---|---|---|
| Within expected range or therapeutic target | Non-heparinized baseline varies by analyzer — Turnaround and screening rules vary by institution; follow local institutional policy as a single universal range | Little or no heparin effect on clotting at time of sample | Expected before heparin bolus; after reversal, confirm protamine effect per protocol |
| Near therapeutic target / borderline | Near institutional lower or upper protocol limit | May require repeat ACT, heparin adjustment, or additional clinical assessment | Communicate trend to procedural team; repeat sample if pre-analytic error suspected |
| Prolonged / above target | Above institutional therapeutic target | Greater anticoagulation than protocol goal — increased bleeding risk | Notify prescriber/perfusion team per protocol; intensify bleeding surveillance |
| Shortened / below target | Below institutional therapeutic target | Insufficient anticoagulation for the procedure — increased clotting risk in circuit or access | Escalate immediately per bypass/ECMO/PCI protocol; prepare for additional heparin only as ordered |
Protocol Targets, Critical Results and Escalation
Critical ACT thresholds are institution- and device-specific. The clinical context — active bleeding, circuit clotting, or hemodynamic change — often matters more than a single second value.
| Critical Finding | Threshold / Value | Immediate Action |
|---|---|---|
| Subtherapeutic ACT during high-dose heparin procedure | Below institutional target with procedural anticoagulation required | Notify perfusionist/prescriber immediately; monitor for circuit or access thrombosis per protocol |
| Supratherapeutic ACT with hemorrhage | Above target with active bleeding or hemodynamic compromise | Escalate according to facility policy; prepare for reversal agents only as authorized |
| ACT not returning toward baseline after reversal | Persistent prolongation after protamine or heparin cessation per protocol | Communicate to surgical/anesthesia team; continue bleeding surveillance and repeat testing as ordered |
Stop routine workflow and escalate according to facility policy when the patient develops uncontrolled bleeding, suspected circuit clotting, stroke or limb ischemia signs, or when ACT results conflict strongly with the clinical picture.
Factors Affecting Results
ACT is highly device- and technique-dependent. Pre-analytic errors and patient factors can mislead anticoagulation decisions if not recognized.
- Prolonged ACT from thrombocytopenia or platelet dysfunction rather than excess heparin
- Prolonged ACT after hypothermia or hemodilution during bypass without true supratherapeutic heparin
- Different analyzer or cartridge type compared with prior values — apparent change may be methodological
- Short ACT from inadequate sample volume, clots in line, or delayed cartridge insertion
- ACT within target while clinical clotting develops in circuit — test does not replace visual and pressure monitoring
- Using ACT to assess low-dose heparin when aPTT or anti-Xa is the appropriate assay
- Heparin dose and timing relative to sample collection
- Platelet count, platelet function, and antiplatelet medicines
- Temperature, hematocrit, and analyzer-specific activator system
ACT and aPTT are not interchangeable; correlation is poor in overlapping ranges. Different point-of-care devices produce different results for the same blood sample. ACT is generally reserved for high-dose heparin settings and is not recommended as the primary monitor for low- to moderate-dose heparin in general ward or ICU patients per reviewed references.
Nursing Responsibilities
Nursing responsibilities center on immediate sampling, accurate device use, trend communication, and bleeding or clotting surveillance during high-risk anticoagulation.
Before the TestDocumentation
Documentation should support anticoagulation traceability and communication during high-risk procedures.
“ACT 412 sec at 0914 (Hemochron cartridge; met institutional CPB target per protocol) drawn from arterial line 3 min after weight-based heparin bolus. Result communicated to perfusionist; no heparin change ordered. Patient hemodynamically stable; no active bleeding observed. Next ACT due per protocol.”
- Date, time, access site, device, and cartridge type
- ACT result in seconds and institutional target range used
- Heparin bolus/infusion rate and time since last dose change
- Who was notified and response per protocol
- Bleeding or clotting observations and hemodynamic trends
- Repeat or invalid sample actions and quality-control notes
Patient and Family Education
Many ACT patients are anesthetized during testing; teaching applies to awake cath-lab or ECMO patients and family when appropriate.
Activated Clotting Time (ACT) NCLEX practice questions
Practice NCLEX-style clinical judgment focused on Activated Clotting Time (ACT) safety and nursing judgment. Use the case tabs (orders, results, assessment, nursing notes), then answer eight Next Gen–style items (including an ordered workflow step) and evaluate outcomes with the answer key.
Select a tab to view orders, results, assessment, and nursing note details for this case.
- Order: ACT — point-of-care, serial monitoring during cardiopulmonary bypass
- Indication: Coronary artery bypass surgery; unfractionated heparin per CPB protocol
- Timing: Baseline ACT due 3 minutes after heparin bolus; q30min per protocol
- Related orders: Weight-based heparin bolus per CPB protocol; ACT target per institutional nomogram; CBC post-bypass
- Result: ACT 285 sec at 09:18 (below institutional protocol target); prior ACT 410 sec at 08:48
- Trend / prior value: Downward ACT trend over 30 minutes; heparin infusion rate unchanged
- Pending tests: Perfusionist review and repeat ACT; no protamine ordered
- Vital signs: HR 88/min, BP 102/58, SpO₂ 99% on ventilator, temp 34.8°C during bypass
- Symptoms: Anesthetized; increased circuit pressure noted by perfusionist; no visible surgical bleeding
- Focused assessment: Arterial line patent; bypass active; last heparin bolus documented 09:15
- Preparation notes: Correct Hemochron cartridge used; sample drawn immediately; handoff from scrub nurse incomplete on heparin rate change
- Collection events: One prior sample rejected for air bubble; repeat ACT pending when case tab reviewed
- Teaching gaps / safety concerns: Subtherapeutic ACT with rising circuit pressure; unclear heparin infusion communication; hypothermia may affect result
Answer key & rationale
Frequently Asked Questions
FAQ
Why is ACT used instead of aPTT during cardiopulmonary bypass?
At high heparin doses used during bypass and similar procedures, aPTT may be too prolonged to be clinically useful and central-lab turnaround is too slow. ACT is a rapid point-of-care test designed for bedside monitoring when intense anticoagulation is required.
Does the patient need to fast before ACT testing?
No special test preparation is usually required. Per clinical laboratory references, fasting is not required for ACT. Follow procedural NPO orders and institutional point-of-care policy separately.
What does a higher ACT result mean?
ACT is measured in seconds. A higher value generally means longer time to clot and greater heparin anticoagulant effect at the time of sampling. Interpret using institutional targets for the specific procedure and analyzer.
Can nurses use ACT to monitor routine IV heparin on a medical ward?
Generally no. Reviewed references indicate ACT is reserved for high-dose heparin settings such as bypass, PCI, ECMO, and selected dialysis contexts. Low- to moderate-dose heparin is usually monitored with aPTT or anti-Xa per hospital protocol.
Are ACT results the same on every machine?
No. Different point-of-care devices and activators produce different ACT values for the same sample. Institutions must use device-specific protocols and targets validated for each analyzer.
When should nurses escalate ACT results?
Escalate when ACT is below or above institutional target with clotting or bleeding concerns, when trends change rapidly, when samples are invalid, or when results conflict with the patient’s clinical status — according to facility policy.
Is ACT ever sent to the central laboratory?
Rarely. The sample must be tested immediately at the point of care because it is not stable for routine transport to a central laboratory. ACT is a bedside or operating-room test in most practice settings.
References
References
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Association for Clinical Biochemistry and Laboratory Medicine. Activated coagulation time (ACT). Lab Tests Online UK.https://labtestsonline.org.uk/tests/act
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Desai, S. S.; et al. Heparin. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026.https://www.ncbi.nlm.nih.gov/books/NBK538247/
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Olson JD; et al. Laboratory monitoring of unfractionated heparin therapy. Arch Pathol Lab Med. 1998;122(9):782-798.https://pubmed.ncbi.nlm.nih.gov/9740136/
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Panigada M; et al. Comparison of Point-of-Care Activated Clotting Time Systems Utilized in a Single Pediatric Institution. J Extra Corpor Technol. 2015.https://pmc.ncbi.nlm.nih.gov/articles/PMC4557434/
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Levy JH; et al. Activated clotting time versus activated partial thromboplastin time for therapeutic monitoring of heparin. Ann Pharmacother. 1996.https://pubmed.ncbi.nlm.nih.gov/8845539/
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De Waele JJ; et al. The use of the activated clotting time for monitoring heparin therapy in critically ill patients. Intensive Care Med. 2003.https://pubmed.ncbi.nlm.nih.gov/12594595/
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Schaden E; et al. Activated Clotting Time (ACT) for Monitoring of Low-Dose Heparin: Performance Characteristics in Healthy Adults and Critically Ill Patients. Clin Appl Thromb Hemost. 2020.https://pmc.ncbi.nlm.nih.gov/articles/PMC7758671/
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A comparison of anti-coagulation monitoring tests in ICU patients receiving a continuous infusion of unfractionated heparin. Sci Rep. 2025.https://pmc.ncbi.nlm.nih.gov/articles/PMC11704084/
Editorial Standards & Medical Review
About the author: Sid A. Abdala Balal, RN, writes evidence-based nursing education focused on diagnostic safety, clinical interpretation, and bedside nursing judgment.
Medical review: This guide is reviewed by Dr. Adam Sayedi, MD, for clinical accuracy, diagnostic safety, and alignment with current standards for Activated Clotting Time (ACT).
Policies: Medical Review Process · Editorial Policy · Correction Policy