What blood work is indicated for a patient presenting with shoulder pain?

Blood Work for Shoulder Pain

Blood work is generally not indicated as a first-line diagnostic approach for patients presenting with shoulder pain unless there is clinical suspicion of infection, inflammatory arthritis, or systemic disease. 1

Diagnostic Approach for Shoulder Pain

Initial Evaluation

• Plain radiographs are the recommended first-line imaging modality for shoulder pain, including:
  • Anteroposterior (AP) view
  • Grashey view
  • Axillary view
  • Scapular Y view 2, 1

When to Consider Blood Work

Blood tests should be ordered selectively based on specific clinical suspicions:

1. Suspected Septic Arthritis

   • Complete blood count (CBC)
   • Erythrocyte sedimentation rate (ESR)
   • C-reactive protein (CRP)
   • Blood cultures
   • Joint aspiration for cell count, culture, and crystal analysis 2

2. Suspected Inflammatory Arthritis

   • Rheumatoid factor (RF)
   • Anti-cyclic citrullinated peptide (anti-CCP) antibodies
   • ESR
   • CRP

3. Suspected Systemic Disease

   • Thyroid function tests (particularly if adhesive capsulitis is suspected, as it can be associated with thyroid disorders) 1
   • Fasting blood glucose or HbA1c (adhesive capsulitis is also associated with diabetes) 1

Imaging Recommendations

After initial radiographs, further imaging should be guided by clinical findings:

• MRI shoulder without IV contrast: Preferred for suspected rotator cuff injury and soft tissue pathology 2, 1
• CT shoulder without IV contrast: Preferred for evaluating bone loss, fracture characterization 2, 1
• Ultrasound: Useful for evaluating rotator cuff and biceps tendon pathology with appropriate expertise 2, 1
• MR arthrography: Gold standard for labral tears, especially in patients under 35 years 1

Common Pitfalls to Avoid

1. Overreliance on blood work: Most shoulder pain is mechanical in nature and does not require laboratory testing. Ordering unnecessary blood tests can lead to incidental findings and unnecessary additional testing.

2. Missing systemic conditions: While uncommon, failing to consider systemic conditions (inflammatory arthritis, infection, metabolic disorders) in appropriate clinical scenarios can lead to delayed diagnosis and treatment.

3. Treating based on imaging alone: Normal radiographs do not rule out soft tissue pathology such as rotator cuff tears, labral tears, and bursitis 1. Conversely, abnormal findings on imaging may not be the source of pain.

4. Delayed arthrocentesis: When septic arthritis is suspected, prompt joint aspiration is crucial and should not be delayed for blood work results 2.

By following this evidence-based approach, clinicians can appropriately utilize blood work in the evaluation of shoulder pain while avoiding unnecessary testing and focusing on the most likely diagnoses based on clinical presentation.