From the Guidelines
Laboratory tests for evaluating suspected appendicitis should include a complete blood count (CBC) with differential, C-reactive protein (CRP), and urinalysis. The CBC often reveals leukocytosis (elevated white blood cell count) typically between 10,000-18,000 cells/mm³ with neutrophilia, which occurs in 80-85% of patients with appendicitis 1. CRP levels are usually elevated within 12-24 hours after symptom onset and can help support the diagnosis, particularly when combined with white blood cell count.
Key Laboratory Tests
- Complete blood count (CBC) with differential
- C-reactive protein (CRP)
- Urinalysis Urinalysis should be performed to rule out urinary tract infections or kidney stones, which can mimic appendicitis symptoms. Additional tests may include a pregnancy test for women of childbearing age to exclude ectopic pregnancy, and liver function tests and pancreatic enzymes (amylase, lipase) if other diagnoses are being considered.
Rationale for Test Selection
These laboratory tests should be interpreted in conjunction with clinical findings and imaging studies, as no single laboratory test can definitively diagnose appendicitis. The tests primarily help to support clinical suspicion and rule out alternative diagnoses. Although the 2024 clinical practice guideline update by the infectious diseases society of america on complicated intra-abdominal infections discusses the use of imaging modalities such as CT scans for diagnosing appendicitis 1, laboratory tests remain essential for supporting the diagnosis and guiding further management.
From the Research
Laboratory Tests for Appendicitis
To evaluate suspected appendicitis, several laboratory tests can be ordered. The following are some of the key tests:
- White Blood Cell (WBC) count: This test measures the number of white blood cells in the blood, which can indicate infection or inflammation 2, 3, 4, 5, 6.
- C-Reactive Protein (CRP) level: This test measures the level of CRP in the blood, which can indicate inflammation or infection 2, 3, 4, 6.
- Neutrophil count: This test measures the number of neutrophils in the blood, which can indicate infection or inflammation 3, 4, 5.
- Neutrophils-to-lymphocytes ratio: This test measures the ratio of neutrophils to lymphocytes in the blood, which can indicate infection or inflammation 5.
- Platelets-to-lymphocytes ratio: This test measures the ratio of platelets to lymphocytes in the blood, which can indicate infection or inflammation 5.
- Red cell distribution width (RDW): This test measures the variation in the size of red blood cells, which can indicate infection or inflammation 5.
- Platelet distribution width (PDW): This test measures the variation in the size of platelets, which can indicate infection or inflammation 5.
Combination of Laboratory Tests
Combining multiple laboratory tests can increase the sensitivity and specificity of diagnosing appendicitis. For example:
- Combining WBC count, neutrophil count, and CRP level can assist in diagnosing appendicitis with a sensitivity of 96% and a specificity of 45% 4.
- Combining WBC count, cytochemical neutrophils, and CRP level can approach a sensitivity of 100% with a specificity in the range of 50% 3.
Imaging Modalities
In addition to laboratory tests, imaging modalities such as ultrasonography (USG) and computed tomography (CT) of the abdomen can be used to diagnose appendicitis. CT abdomen is statistically proven to be a better radiological investigation than USG 2.