IDA: iron-deficiency anemia; UA: unexplained anemia; CDA: chronic disease anemia; CKD: chronic kidney disease; MDS: myelodysplastic syndrome; MCV: mean corpuscular volume; TIBC: total iron-binding capacity; ESR: erythrocyte sedimentation rate; CRP: C-reactive protein; EPO: erythropoietin; CrCl: creatinine clearance; TSH: thyroid-stimulating hormone; MMA: methylmalonic acid. Here, CRP is linked to congenital dyserythropoietic anemia.