Using PCV to Detect Ongoing Hemorrhage
Serial PCV measurements alone are unreliable for detecting ongoing hemorrhage and should not be used as an isolated marker for bleeding. 1
Why PCV is Unreliable for Detecting Active Bleeding
Timing and Hemodilution Issues
A single initial PCV measurement has very low sensitivity (0.5) for detecting hemorrhage requiring surgical intervention, making it inadequate as a standalone diagnostic tool 1
Serial PCV measurements taken at 15 and 30 minutes after arrival show no significant difference between patients with serious injuries versus those without, demonstrating poor early diagnostic value 1
Even when PCV drops ≥6.5% at 15-30 minutes, the sensitivity for detecting severely injured patients remains extremely low (0.13-0.16), though specificity is high (0.93-1.0) 1
A normal PCV on admission does not exclude significant injury or ongoing bleeding, as hemodilution from resuscitative fluids and blood product administration confounds the measurement 1
The Four-Hour Window Problem
Extending serial measurements to four hours improves specificity (0.92-0.96) but sensitivity remains very poor (0.09-0.27) for detecting severe injury 1
This data specifically excluded patients requiring transfusion within four hours, meaning the high specificity only applies to slower bleeding scenarios, not acute hemorrhage 1
What to Use Instead: Traditional Methods
The European trauma guidelines explicitly state that traditional methods of detection for ongoing bleeding should be used: serial clinical evaluation and radiology (ultrasound, CT, or angiography). 1
Superior Monitoring Parameters
Serum lactate is recommended as a sensitive test to estimate and monitor the extent of bleeding and shock (Grade 1B recommendation) 1
Lactate reflects oxygen debt and tissue hypoperfusion from hemorrhagic shock, with survival of 100% when levels normalize within 24 hours versus only 13.6% when elevated >48 hours 1
Hemodynamic parameters including pulse pressure are more reliable early indicators, with narrowed pulse pressure (<55 mmHg in patients ≥61 years, <40 mmHg in younger patients) independently predicting active hemorrhage requiring intervention 2
Clinical Bottom Line
In patients with suspected ongoing hemorrhage, rely on:
- Serial clinical assessment with vital signs (particularly pulse pressure and heart rate) 2
- Lactate measurements and base deficit for metabolic markers of shock 1
- Imaging modalities (FAST ultrasound, CT with contrast, or angiography) to identify bleeding sources 1
- Coagulation parameters (INR, APTT, fibrinogen, platelets) rather than PCV alone 1
A decreasing PCV may reflect continued bleeding, but the patient with significant bleeding may maintain their serial PCV, making it an unreliable sole indicator 1