Diagnosing Sickle Cell Crisis: Clinical Diagnosis Without Required Laboratory Confirmation
The diagnosis of sickle cell crisis is entirely clinical, based on the patient's self-report of pain—no specific laboratory test is required or diagnostic for an acute vaso-occlusive pain episode. 1
Clinical Diagnosis is Primary
- Trust the patient's report of typical pain symptoms and act promptly, as patients with sickle cell disease and their caregivers know their disease best. 1
- The diagnosis requires only the patient's description of pain consistent with their usual crisis pattern—no laboratory abnormalities are necessary for diagnosis. 1
- Pain typically affects fingers in infancy (dactylitis) and long bones, sternum, ribs, or back in older children and adults. 1
Laboratory Tests: For Complications, Not Diagnosis
While no lab confirms the diagnosis of vaso-occlusive crisis itself, obtain the following to assess severity and detect life-threatening complications:
Essential Initial Labs
- Complete blood count (CBC) to compare hemoglobin against the patient's baseline (typically 6-9 g/dL in HbSS). 2, 3
- Reticulocyte count to assess bone marrow response to hemolysis and rule out aplastic crisis. 2, 3
- Hemolysis markers: bilirubin (total and direct), lactate dehydrogenase (LDH), and aspartate aminotransferase (AST) are elevated due to chronic red cell breakdown. 2
- Renal function: BUN and creatinine to detect acute kidney injury from vaso-occlusion. 2
- Liver function tests: AST, ALT, and alkaline phosphatase may be elevated with hepatobiliary involvement. 2
Critical Pitfall: Sickle Cells on Smear Are NOT Diagnostic of Crisis
- Sickle cells are chronically present on peripheral smears in patients with sickle cell disease and do not distinguish acute crisis from baseline. 1
- The presence of sickle cells confirms the underlying disease but does not indicate an acute event. 3
Which Labs Indicate Specific Complications (Not Typical Crisis)
Splenic Sequestration Crisis
- Hemoglobin drop >2 g/dL below baseline with rapidly enlarging spleen and mild-to-moderate thrombocytopenia. 4, 1
- This is NOT a typical vaso-occlusive crisis and requires urgent transfusion. 4
Transient Aplastic Crisis
- Reticulocyte count <1% (substantially decreased) with worsening anemia compared to baseline. 4, 1
- Usually caused by parvovirus B19 infection. 4
Acute Chest Syndrome (Life-Threatening)
- New infiltrate on chest radiograph with respiratory symptoms, chest pain, or hypoxemia. 1, 2
- Obtain arterial blood gas to evaluate oxygenation and acid-base status. 2
- Blood cultures if infection suspected. 2
- This carries up to 13% all-cause mortality—exclude this urgently in any patient with chest pain. 1
Stroke
- Obtain CBC, reticulocyte count, type and crossmatch, and non-contrast CT or MRI to exclude hemorrhage. 4
- Review previous transcranial Doppler results if available, especially in children. 2
Management Implications
- Administer aggressive parenteral opioid analgesia promptly once the patient reports typical crisis pain. 1
- Use scheduled around-the-clock dosing or patient-controlled analgesia (PCA) for severe pain. 1
- Do NOT delay treatment waiting for laboratory results—the diagnosis is clinical. 1
- Avoid factors that precipitate sickling: dehydration, hypoxia, acidosis, hypothermia, and inadequate pain control. 4
Common Pitfalls to Avoid
- Do not rely on hemoglobin level alone to determine transfusion need—consider the patient's baseline and clinical status. 2
- Do not transfuse for uncomplicated vaso-occlusive pain crisis—these episodes are treated with hydration and analgesia, not transfusion. 5
- Screen for recent transfusion history at every ED visit, as delayed hemolytic transfusion reactions can mimic vaso-occlusive crisis and worsen with additional transfusions. 6, 7, 8
- Interpret all laboratory values against the patient's known baseline, as many patients have chronic abnormalities. 2