What is the most appropriate initial laboratory test for a 63-year-old man with a 3-month history of constant, worsening low back and rib pain?

Prostate-Specific Antigen (PSA) Testing is the Most Appropriate Laboratory Test for a 63-Year-Old Man with Worsening Low Back and Rib Pain

For a 63-year-old man presenting with a 3-month history of constant, worsening low back and rib pain with anterior Chapman reflex points along the posterior iliotibial band bilaterally, prostate-specific antigen (PSA) testing is the most appropriate initial laboratory test.

Rationale for PSA Testing

The clinical presentation strongly suggests the possibility of metastatic prostate cancer:

• 63-year-old male (high-risk demographic)
• Constant, worsening low back and rib pain for 3 months
• No history of trauma
• Anterior Chapman reflex points (can indicate referred pain from visceral organs)

Why PSA is the Best Choice:

1. Age-appropriate screening: The patient is in the age group where prostate cancer incidence rises significantly
2. Symptom pattern: Persistent low back and rib pain without trauma is a classic presentation of metastatic prostate cancer to bone
3. High diagnostic yield: PSA has high sensitivity for detecting advanced prostate cancer, with studies showing PSA levels >4.0 μg/L having significant predictive value 1

Differential Considerations

While several conditions could cause the patient's symptoms, the pattern strongly suggests bone metastasis:

• Ankylosing spondylitis: While this could present with inflammatory back pain, the patient's age (onset typically <45 years) and the presence of rib pain make metastatic disease more likely 2
• Osteoporosis with vertebral fractures: Possible but less likely without trauma history
• Primary bone malignancy: Less common than metastatic disease at this age

Evaluation Algorithm

1. Obtain PSA level

   • If elevated (>4.0 ng/mL), proceed to imaging and urology referral
   • Even PSA levels between 2.5-4.0 ng/mL may warrant further investigation in this symptomatic patient 3

2. If PSA is markedly elevated:

   • Bone scan to evaluate for metastatic disease
   • CT or MRI of spine and pelvis
   • Prostate biopsy for definitive diagnosis

3. If PSA is normal or only mildly elevated:

   • Consider additional testing including:
     • Complete blood count
     • Comprehensive metabolic panel
     • Erythrocyte sedimentation rate (ESR)/C-reactive protein (CRP)
     • Imaging of the spine and ribs

Clinical Pearls and Pitfalls

• High PSA levels can indicate extensive metastatic disease: Case reports document PSA levels >20,000 ng/mL in asymptomatic patients with diffuse bone metastases 4
• Don't delay diagnosis: The average delay in diagnosing metastatic prostate cancer can significantly impact mortality and quality of life
• PSA interpretation should be age-specific: Age-specific reference ranges improve specificity, with higher thresholds for older men 5
• Early PSA testing has predictive value: A single PSA test before age 50 can predict advanced prostate cancer diagnosed up to 25 years later 6
• Don't be misled by normal inflammatory markers: Normal ESR/CRP doesn't rule out metastatic disease
• Chapman reflex points: These tender points can indicate referred pain from visceral organs, including the prostate

Conclusion

Given the patient's age, gender, and symptom pattern of constant, progressive low back and rib pain without trauma, PSA testing represents the most appropriate initial laboratory test to evaluate for metastatic prostate cancer, which is the most concerning and potentially life-threatening condition in the differential diagnosis.