Laboratory Testing for Left Lower Quadrant Abdominal Pain
Order a complete blood count (CBC) with differential, C-reactive protein (CRP), and consider urinalysis as your initial laboratory workup for isolated left lower quadrant pain. 1, 2
Essential Laboratory Tests
Complete Blood Count with Differential
- White blood cell count with differential is critical to identify leukocytosis, which when combined with left lower quadrant pain and fever forms the classic triad for diverticulitis (though present in only 25% of cases). 1, 2
- A left shift >75% suggests bacterial infection and helps risk-stratify patients. 3
- The CBC also screens for anemia that might suggest chronic bleeding from malignancy or inflammatory bowel disease. 1
C-Reactive Protein
- CRP >170 mg/L predicts severe diverticulitis with 87.5% sensitivity and 91.1% specificity, making it highly valuable for risk stratification. 2, 3
- When all three criteria are present (left lower quadrant tenderness, CRP >50 mg/L, and absence of vomiting), diagnostic accuracy for diverticulitis reaches 97%, though this occurs in only 24% of patients. 3
- CRP helps distinguish between uncomplicated and complicated disease, though 39% of patients with complicated episodes have CRP below 175 mg/L, so normal CRP does not exclude serious pathology. 2
Additional Laboratory Tests to Consider
- Lactate level should be obtained if the patient appears systemically ill, as elevated lactate indicates sepsis and metabolic derangement requiring aggressive resuscitation. 2
- Blood cultures are indicated if fever is present or sepsis is suspected. 2
- Urinalysis helps exclude urinary tract infection or nephrolithiasis as alternative diagnoses. 1
- Beta-hCG testing should be obtained in all women of reproductive age before proceeding with imaging to exclude ectopic pregnancy. 1
Critical Pitfalls to Avoid
- Do not rely on laboratory values alone to determine severity or guide treatment decisions. Clinical examination combined with laboratory findings has a misdiagnosis rate of 34-68% for diverticulitis. 1, 3
- Do not assume normal inflammatory markers exclude serious pathology. Only 25% of diverticulitis patients present with the classic triad of left lower quadrant pain, fever, and leukocytosis. 1, 2
- Do not order a comprehensive metabolic panel (CMP) routinely unless there are specific clinical indicators such as right upper quadrant pain, liver disease, heart disease, jaundice, or hepatomegaly, as this adds unnecessary cost without improving diagnostic yield in most left lower quadrant pain cases. 4
Imaging Remains Essential
Laboratory testing alone is insufficient—CT abdomen and pelvis with IV contrast (rated 8/9 by the American College of Radiology) remains the definitive diagnostic test with 98% accuracy for identifying the cause of left lower quadrant pain and detecting complications such as abscess, perforation, or fistula that determine appropriate treatment. 1, 3