Determination of occult haemorrhage is an essential part of trauma assessment. We evaluated the diagnostic utility of decreasing haematocrit (DeltaHct) in detecting major injury. Additionally, we tested the correlation between the volume of infused intravenous fluid (IVF) and DeltaHct.
Methods: Prospective observational study at a level one trauma centre.
Inclusion criteria: Patients with suspected major injury. exclusion criteria: Patients who received blood transfusion in the first 4 h, and those who deceased or were transferred to other units before the completion of the observation period (4 h). We measured IVF and DeltaHct at 4 h after triage. We classified patients as having minor or major injury on the basis of injury severity score > or =15. Receiver Operating Characteristic (ROC) curve was used to test the diagnostic performance of DeltaHct in identifying major injury. We tested the operating characteristics of DeltaHct cut-off values of 5 and 10 in detecting major injury. We also measured the correlation of IVF and DeltaHct in a subgroup of patients with low potential for blood loss (ISS<3) to account for possibility of haemodilution.
Results: Four hundred and ninety-four patients (convenience sample) were enrolled (age 36+/-17 years, 82% male, 57% blunt trauma). Sixty-three patients (13%) had major injury. The area under the ROC curve for DeltaHct was not significantly different from the unity line (p=0.20). DeltaHct-4 h>5 points had a sensitivity of 40% (95% CI, 29-52%), specificity of 94% (95% CI, 92-96%), likelihood ratio for a positive test (LR+) of 7.1 (95% CI, 4.4-11.7), and likelihood ratio for a negative test (-LR) of 0.64 (95% CI, 0.52-0.78) in identifying major trauma. DeltaHct-4 h>10 points had sensitivity of 16% (95% CI, 9-27%), specificity of 95% (95% CI, 92-0.96%), +LR of 3.0 (95% CI, 1.5-5.9), and -LR of 0.89 (95% CI, 0.80-0.99). In our subgroup analysis, we detected no significant correlation (p=0.09) between the IVF and DeltaHct-4 h.
Conclusions: DeltaHct-4 h>5 or 10 points is suggestive of major injury (high specificity and +LR). However, the failure to drop the Hct cannot be used to rule out major injury (low sensitivity and -LR).