How Low Can You Go
Platelets, Penguins & Ghost Policies
An evidence-based recalibration of procedural platelet count thresholds
No verdict yet. Just the facts as they were presented.
No verdict yet. Just the facts as they were presented.
Scan to join the quiz
Results
Ghost Policies: What Are They?
An unwritten, arbitrary platelet count threshold — passed down by word-of-mouth, found in no published guideline, enforced as if it were institutional policy.
Example: “Plt < 80K? No epidural.”
- Never written down in any departmental protocol
- Never evidence-based — no RCT supports it
- Contradicted by SOAP 2021, ANZ ITP 2022, AAGBI 2013
- Yet it determines whether a patient receives neuraxial anaesthesia
What other ghost policies do you know?
Well-Recognised Ghost Policies
in Anaesthesiology
- “Nil by mouth after midnight”
Rigid 6–8 h fasting — despite clear fluids clearing the stomach in <2 h (ASA 2017/2023; ESA-IC 2022) - “Hold all regular meds — patient is NPO”
ASA 2012: essential meds should continue with sips of water. β-blocker withdrawal → 2–4× perioperative MI risk - “Cricoid pressure prevents aspiration”
Sellick 1961 (n=26), never proven in an RCT. NAP4: aspiration in 50% of airway deaths regardless. Birenbaum 2019 RCT: no difference - “Preload with crystalloid before spinal”
Ni 2017 meta-analysis (10 RCTs, n=824): preload 57.8% hypotension vs coload 47.1% (OR 1.62). Vasopressors are what matter - “Trendelenburg for hypotension”
Geerts 2012: increases preload for ≤1 min — baroreceptor resetting eliminates the effect. Leg raise more effective, plus no ventilation impairment or ICP rise - “Aspirin = no neuraxial”
ASRA 2025: NSAIDs “do not create a level of risk that will interfere with neuraxial block.” Confusion with P2Y12 inhibitors (clopidogrel) which DO require 5–7 day hold - “Routine coagulation screen before neuraxial”
ASA guidelines: history & exam sufficient. van Veen 2010: routine PT/APTT has near-zero predictive value. Chee 2008: “not recommended” - “Spinal contraindicated in severe aortic stenosis”
Titrated epidural or low-dose spinal may be safer than GA — individualised risk assessment, not an absolute - “No adrenaline in digital blocks”
Ilicki 2015: 2,797 blocks, zero ischaemic complications. The 48 pre-1950 cases were procaine (pH ~1), not adrenaline. 1,111 modern cases — zero necrosis - “Ketamine contraindicated in raised ICP”
Zeiler 2018 systematic review: no ICP elevation in TBI. 1970s studies had uncontrolled CO₂ — ICP rise was CO₂-mediated - “No Hartmann's in renal failure — the potassium will cause hyperkalaemia”
Contains only 5 mmol/L K+ — less than a banana. SMART secondary analysis 2021: patients WITH hyperkalemia had less progression to severe K+ and half the need for RRT with balanced crystalloids vs saline. The “safe” saline makes it worse (hyperchloremic acidosis → transcellular K+ shift)
How Ghost was born
The Cost of Ghost Policies
Clinical Harm
- Denying neuraxial → more general anaesthetics
- GA in obstetrics: significant morbidity and mortality
- Unnecessary platelet transfusions → TRALI, TACO, alloimmunization
- Delays, prolonged admissions, wasted blood products
NZ Medicolegal Risk
- HDC Right 4(2): services must comply with professional standards → MCNZ requires evidence-based practice
- Right 6: patients entitled to know guidelines support proceeding at ≥70K
- Bolitho: practice contradicted by all published guidelines cannot withstand logical scrutiny
- “You must always be prepared to explain your decisions” — MCNZ Good Medical Practice
What Guidelines Actually Say
| Guideline | Recommendation | Reference |
|---|---|---|
| SOAP 2021 | ≥70K → Proceed | 50–70K → Competing risks may justify | <50K → Avoid | SOAP 2021 Interdisciplinary Consensus Statement on Neuraxial Procedures in Obstetric Patients with Thrombocytopenia. Anesth Analg 2021;132:1531–1544. PMID: 33861047 |
| AAGBI / RA-UK 2013 | ITP/Gestational: 50–75K increased risk, 20–50K high risk | Pre-eclampsia: <75K very high risk (if abnormal coags) | Harrop-Griffiths W, et al. Regional anaesthesia and patients with abnormalities of coagulation. Anaesthesia 2013;68:966–972. PMID: 23905877 |
| ANZ ITP 2022 | ≥70 × 10⁹/L is reasonable for neuraxial (GRADE 2D) | Choi PY-I, et al. Australian and New Zealand consensus statement on the management of immune thrombocytopenia in pregnancy. Med J Aust 2022;217:43–51. PMID: 34628650 |
| Bauer Meta-analysis 2019 | Inflection point at 75K — below this, risk increases (19,000+ procedures) | Bauer ME, et al. Lumbar neuraxial procedures in thrombocytopenic patients: systematic review and meta-analysis. J Clin Anesth 2019;57:103–110. PMID: 31810860 |
| MPOG 2017 | 573 neuraxial with Plt <100K — zero epidural haematomas | Lee LO, et al. Risk of Epidural Hematoma after Neuraxial Techniques in Thrombocytopenic Parturients. Anesthesiology 2017;126:1053–1063. PMID: 28383323 |
Zero Observations ≠ Zero Risk
Interpreting “Zero”: The Rule of Three
What are the chances of seeing a penguin on the way to work? Zero. But does that mean the probability is exactly zero? Of course not — a zoo escapee is astronomically unlikely, but not impossible. Observing zero events is not the same as zero risk. This is the statistical problem at the heart of every platelet threshold guideline.
The Rule of Three
- Hanley & Lippman-Hand, JAMA 1983 — a landmark paper addressing exactly this problem
- Calculates the maximum possible risk with 95% confidence when zero events are observed
- Formula: Maximum Risk ≈ 3 / n (where n = sample size)
“If you flip a coin 3 times and get zero heads, you'd have no confidence the coin was fair. But flip it 300 times and still get zero heads — you're confident the probability of heads is less than about 1%.”
No penguins in 300 commutes → you're confident the daily penguin probability is under ~1%. Same logic, different stakes.
Applying It to the Obstetric Data
Lee et al. (2017): 0 SEH in 1,524 neuraxial procedures with Plt <100K
- Maximum Risk ≈ 3 / 1,524
- Maximum Risk ≈ 0.00197
- Maximum Risk ≈ 0.2% (or 1 in 500)
We can be 95% confident that the true risk of spinal epidural haematoma in thrombocytopenic parturients, at the platelet counts studied, is no higher than 0.2% — roughly 1 in 500.
This turns an uncertain “zero” into a confident, quantifiable risk ceiling that can be weighed against the known risks of general anaesthesia.
Source: Hanley JA, Lippman-Hand A. If Nothing Goes Wrong, Is Everything All Right? Interpreting Zero Numerators. JAMA 1983;249:1743–1745.
Rule of Three: Limitations & Why We Still Use It
Critical Limitations
- It's an approximation. The “3” is a convenient rounding of −ln(0.05) = 2.9957
- Assumes perfect data. Doesn't account for selection bias (academic centres only) or publication bias (zero-event studies less likely published)
- Ignores prior knowledge. A Bayesian approach would start with our existing belief that SEH is rare — the true estimated risk would be even lower
Why We Still Use It
- Simple and universal. All major papers in this field use it — creates a common language for discussing risk
- Usefully conservative. The critiques suggest the true risk is likely even lower than 0.2%
- Clinically actionable. ≤0.2% max SEH risk (≤1:500) puts a concrete ceiling on what was an unknown. GA carries its own real risks (failed intubation 1:224–1:808). Both matter — ghost policies ignore both sides of the ledger.
By using the 0.2% figure, we are presenting a conservative, worst-case scenario that is still incredibly reassuring compared to the alternatives.
Critique informed by: Winkler RL, et al. J Am Stat Assoc 2002. Bayesian perspective: Gelman A, et al. Bayesian Data Analysis 3rd ed. 2013, Chapter 2.8.
The Hidden Risk: GA vs Neuraxial
General Anaesthesia (Obstetric)
1:224–1:808
Failed tracheal intubation in obstetric GA (range: Quinn BJA 2013 → DREAMY 2021)
Of those failed intubations, case fatality rate:
1:90
Maternal deaths per failed intubation (Kinsella, IJOA 2015)
Absolute risk of maternal death from GA (airway):
≈1:20,000–1:72,000
= failed intubation rate × case fatality rate
- Aspiration: full stomach in labour
- Hypertensive response to laryngoscopy
- Uterine atony from volatile agents
- No neuraxial opioids for post-op analgesia
Spinal Epidural Haematoma
~1:200,000
General obstetric population (Moen, Anesthesiology 2004; NAP3, 2009)
Zero cases
In 573 neuraxials with Plt <100K (MPOG 2017)
Mitigations:
- 95% of SEH present symptoms within 48h
- Early decompressive laminectomy (<8h) is critical
- Enhanced neurological monitoring detects signs
- Low-concentration LA + opioid preserves motor function
Why Platelet Count Can Mislead
- Platelet count measures quantity, NOT function
- ITP / gestational: low count but young, large, hyperfunctional platelets — count underestimates haemostatic capacity
- Cirrhosis / liver disease: normal count may mask severe platelet dysfunction
- CKD / uraemia: normal count + dysfunctional platelets
- No correlation between platelet count and surgical bleeding (Slichter, Transfus Med Rev 2004)
- Bleeding time: abandoned — no predictive value (Lind, Blood 1991)
TEG / ROTEM: Looking Beyond the Count
Viscoelastic Testing
- TEG MA predicts thrombocytopenia: AUC 0.92 (Bhardwaj 2017)
- Sonoclot PF correlates with platelet count: r = 0.85
- ROTEM INTEM MCF correlates with count: r = 0.46
- High negative predictive value for post-op bleeding
Clinical Role
- SOAP 2021: insufficient evidence for routine use — consider in equivocal cases
- PFA-100: insufficient evidence (SOAP, AAGBI)
- Best used when count is borderline and aetiology uncertain
- Normal TEG/ROTEM is reassuring; abnormal should prompt caution
Workup for the Low Platelet Count Patient
History & Exam
- Bleeding history (epistaxis, gingival, menorrhagia, bruising)
- Medications (heparin, NSAIDs, aspirin, anticonvulsants)
- Previous platelet counts — acute vs chronic?
- Hepatosplenomegaly, lymphadenopathy, petechiae
- Pregnancy: pre-eclampsia features, BP, urinalysis
Laboratory Workup
- FBC + blood film (pseudothrombocytopenia? schistocytes?)
- Coagulation screen (PT, aPTT, fibrinogen)
- Liver function tests, creatinine
- TEG/ROTEM — if available and count borderline
Pattern Recognition
| Aetiology | Count | Function | Bleeding Risk |
|---|---|---|---|
| Gestational | ↓ | Normal/↑ | Low |
| ITP | ↓↓ | Normal/↑ | Variable |
| Pre-eclampsia/HELLP | ↓ | ↓ | High |
| Liver disease | Variable | ↓↓ | High |
| DIC | ↓↓ | ↓↓ | Very high |
Decision Framework
- ≥70K + no coagulopathy + reassuring history → proceed
- 50–70K + ITP/gestational → risk-benefit discussion
- <50K or concerning aetiology → consult haematology
The Aetiology Matters More
Than the Count
ITP · Pre-eclampsia · Cirrhosis · Sepsis
NZ & Australian Guidelines
ANZCA
- Endorses NBA Patient Blood Management Guidelines (2023–24)
- NBA Module 2: Perioperative (ANZCA endorsed)
- NBA Module 5: Obstetrics (ANZCA endorsed)
- No standalone ANZCA platelet threshold guideline exists
- References AAGBI/RA-UK 2013 in practice
- ANZCA PS08: safety-focused
ANZ ITP Consensus 2022
- ≥70 × 10⁹/L is reasonable for neuraxial anaesthesia
- GRADE 2D (weak recommendation, low quality evidence)
- Published in MJA — official ANZ haematology position
- Consider haematology referral for counts <50K
- IVIg or corticosteroids can boost pre-delivery counts
- “Individual risk-benefit assessment is essential”
NZ Blood Service
- NZBS follows ANZSBT guidance
- Not procedure-specific thresholds
- Prophylactic: Plt <10K (no bleeding) or <20K (with risk factors)
- Therapeutic: active bleeding + Plt <50K
- One adult dose: raises Plt by ~30–50 × 10⁹/L
- ABO-identical preferred when available
ANZCA has no independent platelet threshold guideline — it endorses NBA and ANZ ITP consensus. AAGBI 2013 and SOAP 2021 are the most clinically useful references.
Practical Decision Algorithm for Neuraxial
① Assess Aetiology
ITP / Gestational?
(vs pre-eclampsia, DIC, sepsis, liver disease)
Aetiology determines true bleeding risk
② Check Trend
Stable or rising? → more permissive
Falling rapidly? → more cautious
Trajectory matters more than absolute nadir
③ Platelet Count
≥70K → Proceed
(SOAP / AAGBI)
50–70K → Risk-benefit discussion
<50K → Avoid; consult haematology
④ Risk-Benefit Analysis
GA risk vs SEH risk. Difficult airway? Obesity? Labour? GA may be the RISKIER option. → Document reasoning.
⑤ Mitigations
Experienced operator. Low-concentration LA + opioid mix. Enhanced neuro monitoring × 48h. Educate patient re: red flags.
Adapted from: SOAP 2021, AAGBI 2013, Bauer et al. 2019. Always document risk-benefit discussion and monitoring plan.
Replace Ghost Policies With Evidence
| # | Recommendation | Rationale |
|---|---|---|
| 1 | Individualised Risk-Benefit Assessment | Replace rigid thresholds with documented clinical judgement |
| 2 | ≥70K = Evidence-Based Green Zone | SOAP, AAGBI, ANZ ITP consensus all support neuraxial at ≥70K |
| 3 | GA Is NOT the “Safe” Default | Failed intubation 1:224–1:808; case fatality per failed attempt 1:90 — GA has real, quantifiable risks that should factor into the decision alongside SEH risk |
| 4 | Platelet Count ≠ Function | ITP: low count, normal function. Pre-eclampsia: opposite. Aetiology matters |
| 5 | Document & Audit | Record aetiology, trend, guidelines, risk-benefit. Audit neuraxial denial rates |
| 6 | Mitigate Bleeding Risk | US-guided technique + experienced operator + atraumatic needle + low-concentration LA |
Our 78K patient? Gestational thrombocytopenia, no bleeding history, Plt 78K — well above the SOAP/AAGBI/ANZ ITP ≥70K threshold. The haematologist was right to proceed. Dexamethasone was unnecessary. ≤0.2% max SEH risk. Failed obstetric GA intubation 1:224–1:808. The only ghost policy in that consultation was the 80K rule.
If you see zero penguins in 1,524 commutes, you're ≤0.2% confident of seeing one tomorrow. Same data, same logic, applied to our patients.
Procedure Thresholds at a Glance
Invasive Procedures
| Procedure | Plt/μL | Source |
|---|---|---|
| CVC (US-guided, IJ/SCV) | 20,000 | BCSH 2016; PACER: ≥30K for tunneled/haem |
| Lumbar Puncture | 40,000 | van Veen 2009; BCSH 2016 |
| Arterial Line (radial) | No specific | SIR — compressible site |
| PICC Line | 20,000 | Similar to CVC; compressible |
| Intercostal Drain | 50,000 | NICE NG24 |
| General / Abdominal Surgery | 50,000 | NICE NG24; 50–75K for high-risk |
Peripheral Nerve Blocks
| Risk Tier | Plt/μL | Examples |
|---|---|---|
| ● Low (superficial, compressible) | ≥50K | Fascia iliaca, femoral, axillary, popliteal, ankle/wrist |
| ● Intermediate (deeper, partial) | ≥50–75K | Interscalene, supraclavicular, infraclavicular, adductor canal |
| ● High (deep, non-compressible) | ≥75K (treat as neuraxial) | Lumbar plexus, deep cervical, stellate, coeliac |
Sources: PACER — van Baarle et al. NEJM 2023. PNB — AAGBI/RA-UK 2013 Table 2; ASRA 5th Ed 2025. Invasive — BCSH 2016; NICE NG24; SIR 2019.
References
[1] SOAP 2021 — Neuraxial procedures in thrombocytopenic obstetric patients. Anesth Analg. PMID 33861047
[2] AAGBI/RA-UK 2013 — Regional anaesthesia & coagulation abnormalities. Anaesthesia. PMID 23905877
[3] Bauer 2019 — Neuraxial procedures in thrombocytopenia: meta-analysis. J Clin Anesth. PMID 31810860
[4] van Veen 2010 — Spinal haematoma risk in thrombocytopenia. Br J Haematol. PMID 19775301
[5] Lee MPOG 2017 — Epidural hematoma in thrombocytopenic parturients. Anesthesiology. PMID 28383323
[6] van Baarle PACER 2023 — Platelet transfusion before CVC placement. NEJM. PMID 37224197
[7] Estcourt Cochrane 2016/2018 — No RCTs on platelet thresholds for neuraxial. PMID 29709077
[8] NICE NG24 2015 — Blood transfusion guideline. nice.org.uk/guidance/ng24
[9] BCSH 2017 — Guidelines for platelet transfusions. Br J Haematol. PMID 28009056
[10] ANZ ITP 2022 — Management of adult ITP in Australia & NZ. Med J Aust. PMID 34628650
[11] NBA PBM 2023–24 — Patient blood management guidelines. blood.gov.au
[12] NAP3 2009 — Major complications of neuraxial block in UK. Br J Anaesth. PMID 19139027
[13] Bhardwaj 2017 — Coagulopathies: TEG, ROTEM, Sonoclot analysis. Ann Card Anaesth. PMID 28393783
[14] Kinsella 2015 — Failed intubation in obstetric GA: review. Int J Obstet Anesth. PMID 26303751
[14a] Quinn 2013 — Failed intubation: UK case-control. Br J Anaesth. PMID 22986421
[14b] DREAMY 2021 — GA for obstetric surgery in England. Anaesthesia. PMID 32959372
[15] Moen 2004 — Neurological complications after neuraxial block. Anesthesiology. PMID 15448529
[16] SIR 2019 — Periprocedural bleeding risk management. J Vasc Interv Radiol. PMID 31229333
[17] Hanley 1983 — Rule of Three: interpreting zero numerators. JAMA. PMID 6827763
[18] Slichter 2004 — Platelet count & bleeding risk. Transfus Med Rev. PMID 15248165
[19] Lind 1991 — Bleeding time does not predict surgical bleeding. Blood. PMID 2043759
Abbreviation Key
Guidelines & Organisations
SOAP — Society for Obstetric Anesthesia and Perinatology
AAGBI — Association of Anaesthetists of GB & Ireland
ANZCA — Australian & NZ College of Anaesthetists
ANZ ITP — ANZ Immune Thrombocytopenia Consensus
BCSH — British Committee for Standards in Haematology
NICE — National Institute for Health and Care Excellence
NBA — National Blood Authority (Australia)
NZBS — New Zealand Blood Service
ANZSBT — ANZ Society of Blood Transfusion
SIR — Society of Interventional Radiology
MCNZ — Medical Council of New Zealand
HDC — Health and Disability Commissioner
Regulatory
HDC Code — NZ Code of Health and Disability Services Consumers' Rights
Bolitho — Bolitho v City and Hackney HA [1997] (logical basis test)
Databases & Trials
MPOG — Multicenter Perioperative Outcomes Group
PACER — Platelet Transfusion before CVC Placement trial
NAP3 — Third National Audit Project (RCoA)
DREAMY — GA for Obstetric Surgery in England study
Cochrane — Cochrane Database of Systematic Reviews
Clinical Terms
ITP — Immune Thrombocytopenia
SEH — Spinal Epidural Haematoma
GA — General Anaesthesia
TRALI — Transfusion-Related Acute Lung Injury
TACO — Transfusion-Associated Circulatory Overload
TEG — Thromboelastography
ROTEM — Rotational Thromboelastometry
PFA-100 — Platelet Function Analyzer-100
RCT — Randomised Controlled Trial
CVC — Central Venous Catheter
HELLP — Haemolysis, Elevated Liver enzymes, Low Platelets
DIC — Disseminated Intravascular Coagulation
Thank You
Questions & Discussion
Roman Vasilev · Specialist Anaesthetist · Palmerston North Hospital
Prepared June 2026 — evidence current as of May 2026