What are the laboratory findings in appendicitis (inflammation of the appendix)?

From the Guidelines

Laboratory workup for suspected appendicitis should include a complete blood count (CBC), C-reactive protein (CRP), and urinalysis to support diagnosis, although these tests are not definitive alone. According to the guidelines by the Surgical Infection Society and the Infectious Diseases Society of America 1, a constellation of findings, including characteristic abdominal pain, localized abdominal tenderness, and laboratory evidence of acute inflammation, will generally identify most patients with suspected appendicitis. The CBC often shows leukocytosis (elevated white blood cell count) with neutrophil predominance, while CRP levels are usually elevated and tend to increase with disease progression.

• Key laboratory findings include:
  • Leukocytosis (elevated white blood cell count) between 10,000-18,000 cells/mm³ with neutrophil predominance (>75%)
  • Elevated CRP levels (>10 mg/L)
  • Urinalysis to rule out urinary tract conditions that may mimic appendicitis
• It is essential to note that normal lab values do not exclude appendicitis, especially in early presentation, and imaging studies like ultrasound or CT scan are often needed for confirmation, as recommended by the guidelines 1. The Alvarado score, which incorporates lab findings with clinical symptoms, can help stratify risk. Lab results should always be interpreted alongside the patient's clinical presentation, as appendicitis remains primarily a clinical diagnosis supported by laboratory and imaging findings.

From the Research

Lab Workup for Appendicitis

• The diagnosis of acute appendicitis is based on history, physical examination, laboratory evaluation, and imaging 2.
• Laboratory tests such as complete blood count (CBC) parameters, including white blood cell (WBC) count, neutrophil percentage, and C-reactive protein (CRP) concentration, are commonly used as diagnostic aids in patients with suspected acute appendicitis 3.
• The CBC is a cost-effective and easily-accessible test with acceptable diagnostic accuracy, and it provides fast results that can be used in the diagnosis of appendicitis 4.
• Neutrophil, WBC, and neutrophil-to-lymphocyte ratio (NLR) are helpful and useful parameters for physical examination and other diagnostic methods in diagnosing acute appendicitis and measuring severity 4.

Diagnostic Markers

• Elevated WCC, CRP, and bilirubin can be used as diagnostic markers of acute appendicitis, with significant differences in results between patients with negative and positive appendicitis 5.
• The sensitivity of leucocyte count, neutrophil percentage, and CRP in diagnosing acute appendicitis was 85.8,87.2, and 76.5%, respectively, whereas the specificity was 31.9,33.1, and 26.1%, respectively 3.
• Abnormal laboratory findings cannot reliably deliver a diagnosis of acute appendicitis, but acute appendicitis is very unlikely when leucocyte count, neutrophil percentage, and CRP level are simultaneously normal 3.

Imaging and Diagnosis

• Computed tomography (CT) scans with no contrast or just rectal contrast are becoming the standard in many institutions for diagnosing acute appendicitis 6.
• Specific imaging findings on CT, such as appendiceal dilatation or presence of appendicoliths, can identify patients for whom an antibiotics-first management strategy is more likely to fail 2.
• The use of CT scans has reduced negative appendectomy rates when combined with a physical examination, and assists in ruling out appendicitis 6.