What laboratory tests should be obtained and what threshold values guide blood product replacement in a woman with suspected postpartum hemorrhage?

Laboratory Values and Transfusion Thresholds for Postpartum Hemorrhage

In postpartum hemorrhage, fibrinogen is the single most critical laboratory value to monitor, with levels <2.0 g/L triggering immediate fibrinogen replacement, and viscoelastic testing (ROTEM/TEG) providing the fastest actionable results to guide transfusion decisions. 1

Essential Laboratory Tests to Obtain Immediately

First-Line Tests (Obtain Within Minutes)

• Viscoelastic testing (ROTEM or TEG) should be performed immediately if available, as it provides results within 10-15 minutes compared to 45-60 minutes for standard coagulation tests 1
• FIBTEM A5 <12 mm on ROTEM (equivalent to fibrinogen ≤2.0 g/L) is the critical threshold that predicts progression to severe hemorrhage and need for massive transfusion 1, 2
• Point-of-care hemoglobin measurement via venous blood gas provides rapid assessment of oxygen-carrying capacity 3
• Lactate level >2 mmol/L indicates shock and inadequate tissue perfusion 3

Standard Laboratory Panel

• Complete blood count with hemoglobin and platelet count 3, 4
• Fibrinogen level (Clauss method) - this is the single best predictor of hemorrhage severity, though results take longer than FIBTEM A5 1, 5
• PT/APTT - though these remain normal in most PPH cases and correlate poorly with bleeding severity 5
• Type and crossmatch for blood products 3

Additional Tests for Persistent or Severe Bleeding

• Peripheral blood smear to identify schistocytes indicating microangiopathic hemolysis 4
• Haptoglobin and LDH if hemolysis is suspected (haptoglobin will be low, LDH elevated) 4
• Direct Coombs test to exclude autoimmune hemolysis 4
• Reticulocyte count to assess bone marrow response 4
• Ionized calcium - must be maintained >1.0 mmol/L as hypocalcemia impairs coagulation 1, 3

Critical Threshold Values for Blood Product Replacement

Red Blood Cell Transfusion

• Hemoglobin <7.0 g/dL: Transfuse regardless of symptoms 4, 6
• Hemoglobin 7.0-8.0 g/dL: Transfuse if cardiac disease, ongoing bleeding, or hemodynamic instability present 4, 6
• Expected response: Each unit of packed RBCs should increase hemoglobin by approximately 1 g/dL 4, 6
• Transfusion strategy: Give one unit at a time and recheck hemoglobin before each subsequent unit, except during active massive hemorrhage 3, 6

Fibrinogen Replacement - The Most Critical Intervention

• Fibrinogen <2.0 g/L (or FIBTEM A5 <12 mm): Immediate fibrinogen replacement is indicated 1, 2
• Target fibrinogen level: Maintain ≥2.0 g/L during active bleeding 3, 7
• Normal postpartum fibrinogen: 4-6 g/L, so levels <2.0 g/L represent severe depletion 4, 6
• Dosing: Initial dose of 3-4 g fibrinogen concentrate or 15-20 single donor units of cryoprecipitate 1
• Critical evidence: Fibrinogen correlates best with blood loss (r = -0.48) compared to other coagulation parameters, and early ROTEM-guided fibrinogen replacement reduces progression to massive transfusion from 67% to 0% in women with fibrinogen ≤2.0 g/L 2, 5

Fresh Frozen Plasma (FFP)

• Delay FFP until 4 units of RBCs have been transfused in hemorrhage from atony or trauma, unless early coagulopathy is documented 3
• PT/APTT >1.5 times normal: Consider FFP, though these tests correlate poorly with PPH severity 1, 5
• Ratio-based approach: If using empiric massive transfusion protocol, maintain FFP:RBC ratio of at least 1:2 1
• Important caveat: Standard guidelines for FFP use are rarely appropriate in PPH, as PT/APTT remain normal despite severe bleeding in most cases 5

Platelet Transfusion

• Platelet count <50 × 10⁹/L: Transfuse during ongoing bleeding 1
• Platelet count <100 × 10⁹/L: Transfuse if traumatic brain injury present 1
• Dosing: 4-8 single platelet units or one apheresis pack 1

Calcium Replacement

• Ionized calcium <1.0 mmol/L: Administer calcium chloride immediately 1, 3
• Rationale: Many coagulation factors function poorly below 1.0 mmol/L, and massive transfusion depletes calcium 3

Algorithmic Approach to Laboratory-Guided Transfusion

Step 1: Immediate Assessment (Within 5 Minutes)

1. Activate massive transfusion protocol if blood loss >1500 mL or ongoing rapid bleeding 3, 8
2. Obtain point-of-care hemoglobin and lactate via blood gas 3
3. Send ROTEM/TEG if available, or stat fibrinogen level 1
4. Calculate Shock Index (HR ÷ SBP): >1.0 indicates hemodynamic instability requiring aggressive intervention 4, 6

Step 2: Initial Transfusion Strategy (0-15 Minutes)

• If ROTEM/TEG available: Use FIBTEM A5 to guide immediate fibrinogen replacement if <12 mm 1, 2
• If ROTEM/TEG unavailable: Begin with RBC transfusion and send stat fibrinogen level 3
• Transfuse up to 4 units RBCs before considering FFP unless documented coagulopathy 3
• Administer tranexamic acid 1 g IV within 3 hours of bleeding onset 1, 3

Step 3: Ongoing Resuscitation (15-60 Minutes)

• Recheck hemoglobin 4-6 hours after transfusion to confirm adequate response 6
• Monitor fibrinogen continuously: If <2.0 g/L, give fibrinogen concentrate 3-4 g and repeat as needed 1, 3, 7
• Maintain platelet count >50 × 10⁹/L (>100 × 10⁹/L if head trauma) 1
• Correct ionized calcium to >1.0 mmol/L 1, 3
• Maintain temperature >36°C: Hypothermia severely impairs coagulation factor function 3, 7

Step 4: Persistent Bleeding Despite Initial Measures

• Repeat ROTEM/TEG or coagulation panel to identify specific deficiencies 1
• Consider microangiopathic hemolysis: Check peripheral smear for schistocytes, haptoglobin, LDH 4
• If thrombocytopenia worsening after day 5: Measure ADAMTS13 activity and consider atypical hemolytic uremic syndrome (aHUS), which requires immediate eculizumab 4
• Pelvic ultrasound with Doppler to exclude retained products, hematoma, or ongoing bleeding source 4, 6

Critical Pitfalls to Avoid

Laboratory-Related Errors

• Do not wait for standard coagulation results before initiating treatment in severe hemorrhage - they take 45-60 minutes and correlate poorly with bleeding 1, 5
• Do not rely on PT/APTT to guide FFP transfusion - these remain normal in most PPH cases despite severe bleeding 5
• Do not use visual estimation of blood loss - it consistently underestimates actual loss by 30-50%; use volumetric measurement with weighed sponges 3, 4
• Do not transfuse FFP empirically without documented coagulopathy - this leads to unnecessary transfusion in most cases 3, 5

Physiologic Errors

• Do not allow hypothermia: Temperature <36°C severely impairs coagulation factor function 3, 7
• Do not allow acidosis: pH <7.2 worsens coagulopathy independent of factor levels 3
• Do not forget calcium replacement: Massive transfusion rapidly depletes ionized calcium 1, 3
• Do not overlook hemolysis: Persistent anemia despite transfusion requires evaluation for microangiopathic hemolysis or aHUS 4

Strategic Errors

• Do not delay fibrinogen replacement: Fibrinogen <2.0 g/L is the strongest predictor of progression to massive transfusion, and early replacement dramatically improves outcomes 2, 5
• Do not use fixed-ratio massive transfusion protocols without laboratory guidance: ROTEM-guided strategies reduce transfusion requirements, ICU admissions, and hysterectomy rates compared to empiric protocols 1
• Do not forget tranexamic acid: Must be given within 3 hours of bleeding onset for maximum benefit 1, 3

Special Considerations for Specific Clinical Scenarios

Placental Abruption, Amniotic Fluid Embolism, or Severe Preeclampsia

• Consider early cryoprecipitate or fibrinogen concentrate before RBCs - these conditions cause rapid fibrinogen consumption 3
• Expect fibrinogen <2.0 g/L and prepare for aggressive replacement 3

Post-Cesarean Section with Persistent Anemia

• Retained products are high-risk due to weakened cesarean scar - use transvaginal ultrasound with color Doppler 4
• Each unit of RBCs should increase Hb by 1 g/dL - if response is inadequate, investigate hemolysis or ongoing bleeding 4, 6