What laboratory studies should be ordered for a 70‑year‑old patient with new‑onset right lower‑quadrant abdominal pain while arranging urgent CT imaging?

Laboratory Studies for 70-Year-Old with New-Onset Right Lower Quadrant Pain

Order a complete blood count with differential, comprehensive metabolic panel, C-reactive protein, urinalysis, and lipase immediately while arranging urgent CT abdomen/pelvis with IV contrast. 1, 2

Essential Laboratory Panel

Core Studies (Order Immediately)

• Complete blood count (CBC) with differential – Leukocytosis supports but does not confirm appendicitis; however, approximately 50% of appendicitis cases present with normal white blood cell counts, particularly in early disease 2
• Comprehensive metabolic panel (CMP) – Identifies electrolyte abnormalities, renal dysfunction, and hepatobiliary enzyme elevations that may suggest alternative diagnoses such as choledocholithiasis or hepatic pathology 1
• C-reactive protein (CRP) – Elevated CRP increases the likelihood of acute inflammation, though normal values do not exclude appendicitis or other serious pathology 2
• Urinalysis with microscopy – Essential to exclude urinary tract infection, nephrolithiasis, or pyelonephritis; sterile pyuria may indicate adjacent inflammatory processes such as appendicitis or diverticulitis 2
• Lipase – Elevated levels identify pancreatitis, which can present with right-sided abdominal pain and is among the most common alternative diagnoses in patients presenting to emergency departments with abdominal pain 1

Critical Pitfalls in Laboratory Interpretation

• Do not exclude appendicitis based on normal inflammatory markers – Fever is absent in approximately 50% of appendicitis cases, and normal WBC/CRP are common in early disease 2
• Recognize that elderly patients often have blunted inflammatory responses – Many laboratory tests are nonspecific and may remain normal despite serious intra-abdominal infection in this population 1
• Interpret positive urinalysis cautiously – Sterile pyuria with negative urine culture may reflect adjacent inflammatory processes (appendicitis, diverticulitis) rather than primary urinary pathology 2

Age-Specific Considerations for 70-Year-Olds

• Imaging is especially critical in elderly patients with acute abdominal pain and fever because laboratory findings are frequently nonspecific and may be normal despite serious infection 1
• Clinical assessment alone misdiagnoses acute appendicitis in 34-68% of cases, making laboratory studies adjunctive rather than definitive 2
• The differential diagnosis in this age group extends beyond appendicitis to include right-sided diverticulitis (8% of cases), small bowel obstruction, perforated peptic ulcer, cancer, and mesenteric ischemia 1, 2

Integration with Imaging Strategy

• CT abdomen/pelvis with IV contrast remains the definitive diagnostic test with 85.7-100% sensitivity and 94.8-100% specificity for appendicitis, while simultaneously identifying alternative diagnoses in 23-45% of patients 1, 2
• Laboratory studies guide clinical urgency but should not delay CT imaging – Proceed with urgent CT regardless of laboratory results when clinical suspicion for acute pathology is present 1, 2
• CT identifies critical alternative diagnoses including right colonic diverticulitis, intestinal obstruction (3% of cases), gynecologic pathology (21.6% of alternative diagnoses), and gastrointestinal conditions (46% of alternative diagnoses) 2

Additional Laboratory Studies Based on Clinical Context

• If biliary pathology is suspected (right upper quadrant radiation of pain, jaundice) – Add total and direct bilirubin, alkaline phosphatase, and gamma-glutamyl transferase to identify choledocholithiasis or cholangitis 1
• If perforation or abscess is suspected (peritoneal signs, systemic toxicity) – Obtain blood cultures before initiating antibiotics 1
• If mesenteric ischemia is considered (severe pain out of proportion to examination, cardiovascular risk factors) – Add lactate and arterial blood gas; however, CT angiography is the definitive diagnostic test 1