What laboratory tests suggest amniotic fluid embolism (AFE)?

Laboratory Findings in Amniotic Fluid Embolism

No specific laboratory test can confirm or refute the diagnosis of amniotic fluid embolism—it remains a clinical diagnosis based on the classic triad of sudden hypoxia, hypotension, and coagulopathy. 1

Key Laboratory Findings to Assess

While AFE cannot be diagnosed by labs alone, the following tests help support the clinical diagnosis and guide management:

Coagulation Studies (Most Important)

Disseminated intravascular coagulation (DIC) is the hallmark laboratory finding in AFE, though it may have immediate or delayed onset following cardiovascular collapse. 1

• Obtain immediately: PT/INR, aPTT, fibrinogen, platelet count, D-dimer 1
• Expected findings in DIC:
  • Prolonged PT/aPTT
  • Low fibrinogen (consumptive coagulopathy)
  • Thrombocytopenia
  • Elevated D-dimer
  • Evidence of hemorrhage from venipuncture sites, surgical sites, hematuria, GI bleeding, or vaginal bleeding 1

Additional Laboratory Assessment

• Arterial blood gas: Severe hypoxemia and metabolic acidosis 1
• Complete blood count: Thrombocytopenia, anemia from hemorrhage 1
• Type and crossmatch: For massive transfusion protocol activation 1
• Lactate: Elevated due to tissue hypoperfusion 1

Critical Clinical Context

The Society for Maternal-Fetal Medicine explicitly states that no specific diagnostic laboratory test should be used to either confirm or refute AFE diagnosis (GRADE 1C). 1 This is because:

• The diagnosis is made clinically based on sudden cardiorespiratory collapse in a laboring or recently delivered woman 1
• Laboratory findings serve to assess severity and guide treatment, not to diagnose 1
• Early assessment of clotting status is recommended to enable aggressive management with massive transfusion protocols (GRADE 1C) 1

Common Pitfalls

• Do not delay resuscitation waiting for laboratory confirmation—AFE requires immediate CPR and multidisciplinary team activation 1, 2, 3
• Coagulopathy may not be immediately apparent but can develop rapidly after initial cardiovascular collapse 1, 3
• Avoid confusing primary hemorrhage with coagulopathy leading to hypovolemic shock with true AFE—bleeding from uncontrolled atony followed by consumptive/dilutional coagulopathy is not AFE 1
• The coagulopathy in AFE follows cardiovascular collapse, not the reverse 1

Diagnostic Approach

When AFE is suspected based on clinical presentation (sudden hypoxia, hypotension, seizures, or cardiac arrest in labor/postpartum):

1. Immediately activate multidisciplinary team and begin ACLS 1, 3
2. Draw coagulation studies, CBC, type and crossmatch simultaneously 1, 3
3. Activate massive transfusion protocol if coagulopathy present 1, 3
4. Use labs to guide blood product replacement, not to confirm diagnosis 1