Laboratory Workup for Blood Loss
In patients with suspected blood loss, immediately obtain a complete blood count with platelets, coagulation studies (PT/INR and aPTT), hemoglobin/hematocrit, serum electrolytes, renal function tests (BUN and creatinine), and blood type with cross-match if severe bleeding is suspected. 1
Initial Core Laboratory Panel
The following tests should be obtained immediately when blood loss is suspected:
Complete blood count (CBC) with platelet count to assess the degree of anemia and identify thrombocytopenia that may contribute to ongoing bleeding 1
Hemoglobin and hematocrit measurements are essential markers for quantifying blood loss, though initial values may be falsely normal in early-phase bleeding before hemodilution occurs 1
Coagulation studies including PT/INR and aPTT to identify coagulopathies that may be causing or exacerbating bleeding 1
Serum electrolytes to identify metabolic derangements 1
Renal function tests (BUN and creatinine with calculated GFR) as these are critical for risk stratification and medication dosing 1
Blood glucose to rule out metabolic abnormalities and assess overall metabolic status 1
Blood Typing and Cross-Match
Blood type and cross-match should be ordered immediately in patients with signs of severe bleeding to prepare for possible transfusion 1
This is particularly critical when vital signs are unstable, there is evidence of hemodynamic compromise, or ongoing active bleeding is present 1
Serial Monitoring Strategy
A critical pitfall is relying on a single hemoglobin or hematocrit value, as initial measurements in the normal range may mask early-phase serious bleeding. 1
Repeated hemoglobin/hematocrit measurements should be obtained based on estimated blood loss and clinical signs, as serial measurements significantly increase sensitivity for detecting ongoing blood loss 1
The confounding influence of resuscitation fluids and physiological fluid shifts can affect interpretation, making trending more valuable than isolated values 1
Additional Laboratory Tests Based on Clinical Context
Iron Status Assessment (if chronic blood loss suspected):
Serum ferritin and transferrin saturation to evaluate for iron deficiency from chronic blood loss 1
Ferritin <30 mg/L and/or transferrin saturation <20% indicates absolute iron deficiency 1
Coagulation Monitoring (if coagulopathy suspected):
Fibrinogen concentration should be obtained if coagulopathy is suspected 1
Viscoelastic assays (TEG or ROTEM) when available, provide rapid assessment of coagulation status and can guide targeted therapy 1
If viscoelastic assays are unavailable, obtain standard coagulation tests including platelet count 1
Additional Tests for Specific Scenarios:
Liver function tests in patients with suspected liver disease or alcohol use 1
Cardiac troponin and ECG to identify concurrent cardiac conditions, as significant blood loss can precipitate myocardial ischemia 1
Pregnancy test in women of childbearing age 1
Toxicology screen when drug use (particularly anticoagulants or antiplatelet agents) is suspected 1
Quantitative Blood Loss Assessment
Beyond laboratory tests, quantitative measurement of blood loss should include checking suction canisters, surgical sponges, and surgical drains in perioperative or trauma settings 1
Key Clinical Pitfalls to Avoid
Do not wait for laboratory results to initiate resuscitation in patients with obvious severe bleeding and hemodynamic instability 1
Do not assume normal initial hemoglobin excludes significant bleeding - early measurements before equilibration can be misleadingly normal 1
Do not forget to assess for occult bleeding sources - gastrointestinal bleeding may require referral to gastroenterology if iron deficiency is identified 1
Monitor for perfusion of vital organs using standard vital signs (blood pressure, heart rate, oxygen saturation) in addition to laboratory values 1