What lab results indicate a sickle cell crisis?

Laboratory Tests Indicating Sickle Cell Crisis

A comprehensive laboratory panel including complete blood count, hemolysis markers (reticulocyte count, bilirubin), renal function (BUN, creatinine), liver enzymes (AST, ALT), and coagulation studies (PT, PTT) should be obtained to assess crisis severity and detect organ damage. 1

Essential Laboratory Findings in Acute Crisis

Hematologic Parameters

• Hemoglobin level drops acutely from baseline due to hemolysis, though the absolute value must be interpreted against the patient's chronic baseline (typically 6-9 g/dL in HbSS) 2, 1
• White blood cell count is frequently elevated during acute crisis and correlates with admission decisions; elevations above baseline suggest more severe crisis or infection 1, 3
• Reticulocyte count should be elevated (often >10%) as a normal bone marrow response to ongoing hemolysis; a paradoxically low or dropping reticulocyte count suggests aplastic crisis (often parvovirus B19) or hyperhemolytic crisis 1, 4, 5
• Platelet count may show thrombocytosis during vaso-occlusive episodes, but a precipitous drop suggests hyperhemolytic syndrome or other severe complications 5

Hemolysis Markers

• Total and direct bilirubin are elevated due to accelerated red cell breakdown from chronic and acute hemolysis 1
• Lactate dehydrogenase (LDH) rises with hemolysis and tissue ischemia, though this is often chronically elevated in sickle cell disease 5

Organ Function Assessment

• BUN and creatinine detect acute kidney injury from vaso-occlusion and sickling within renal vasculature 1
• AST and ALT may be elevated with hepatic involvement or ischemia 1
• Alkaline phosphatase increases with hepatobiliary complications 1
• Electrolytes should be monitored for hyperkalemia (seen in hemolysis and renal dysfunction) and other imbalances from dehydration 1, 5

Coagulation Studies

• PT and PTT assess for coagulopathy, which can develop in severe crisis or with hepatic dysfunction 1

Crisis-Specific Laboratory Tests

Acute Chest Syndrome

• Arterial blood gas evaluates oxygenation status and acid-base balance 1
• Blood cultures if infection is suspected as a precipitant 1

Suspected Stroke (Especially in Children)

• Review previous transcranial Doppler results from within 12 months (or 24 months for HbSC/HbSβ+ thalassemia) 2, 1

Priapism

• Corporal blood gas differentiates ischemic from non-ischemic priapism 1

Critical Interpretation Pitfalls

Always compare current values to the patient's baseline laboratory values, as chronic abnormalities are the norm in sickle cell disease 1. A hemoglobin of 7 g/dL may represent a 3 g/dL acute drop from baseline in one patient but be stable in another 2.

A dropping reticulocyte count in the setting of worsening anemia is a red flag for aplastic crisis or hyperhemolytic syndrome, not typical vaso-occlusive crisis 4, 5. Hyperhemolytic syndrome can cause precipitous hemoglobin drops (>4 g/dL in 24-36 hours), thrombocytopenia, and multi-organ failure 5.

Clearly document sickle cell disease on all laboratory request forms to ensure proper sample handling and interpretation by the laboratory 2, 1.

Do not rely solely on hemoglobin levels to guide transfusion decisions; consider the patient's clinical status, baseline hemoglobin, and rate of decline 1.

Pre-operative Laboratory Requirements

For surgical patients, obtain full blood count, urea and electrolytes, and complete red cell antibody screen before any procedure 2. If transfused within 3 months, repeat these tests within 72 hours of surgery 2.