Differential Diagnosis for Anemia and Joint Pain in Adults

Primary Differential Diagnoses

The American College of Rheumatology suggests that advanced age, female gender, and involvement of small joints of hands and feet are highly predictive of Rheumatoid Arthritis (RA) 3
The presence of metatarsal erosions with elevated CRP strongly suggests inflammatory arthritis, particularly RA 3, 4
Anemia of chronic disease commonly accompanies RA and correlates with disease activity 3, 4
The European League Against Rheumatism recommends obtaining rheumatoid factor (RF) and anti-citrullinated protein antibodies (ACPA) immediately, as these are highly predictive of RA diagnosis and prognosis 3, 4
Erosive osteoarthritis targets interphalangeal joints primarily but can affect metatarsophalangeal joints, characterized by abrupt onset, marked pain, inflammatory symptoms, and mildly elevated CRP 1

The American College of Emergency Physicians states that septic arthritis must be excluded urgently in any warm, painful joint with erosive changes 2
Arthrocentesis with cell count, differential, and culture is mandatory before initiating treatment for suspected septic arthritis 2
The American Academy of Orthopaedic Surgeons recommends that monoarthritis of the first MTP joint has 99% sensitivity for gout when presenting acutely 2
Elevated CRP with normal ESR is characteristic of acute crystal inflammation, such as gout 2

The American College of Rheumatology recommends essential first-line tests, including complete blood count with differential to characterize anemia and assess for leukocytosis 3, 4
ESR measurement alongside CRP should be performed at baseline for diagnosis and prognosis 3, 4, 5
RF and ACPA testing are predictive of RA diagnosis even when negative tests don't exclude progression 3, 4

The European League Against Rheumatism suggests that X-rays of hands, wrists, and feet should be performed at baseline, as presence of erosions is predictive for RA and disease persistence 3, 4
Metatarsal erosions help distinguish inflammatory arthritis from degenerative disease 3, 1
Repeat radiographs within 1 year to assess progression 4

The American College of Rheumatology states that anemia and azotemia can artificially elevate ESR independent of inflammatory activity 5
Normal ESR does not exclude inflammatory arthritis; CRP may be more sensitive in acute crystal arthropathy 2
Serum uric acid may be normal during acute gout flare 2
Negative RF and ACPA do not exclude progression to RA 3, 4