Whether positive or negative, what effects does iron deficiency have on esr?

No effect by Fe def. The ESR may be useful in differentiating iron deficiency from anemia of chronic disease in patients with a background chronic inflammatory condition such as rheumatoid arthritis. Unfortunately, the ESR is neither sensitive nor specific when used in isolation. An elevated ESR can occur in so many conditions. That's why history taking, physical exam, and collection of other lab data are important.
Not much. If ESR is low, is reassuring is not inflammatory process, but high ESR doesnt mean inflammatory anemia or any diagnosis in particular. You can have high or low ESR with or without iron deficiency, have to put in context with other labs and clinical scenario.
ESR to Eval Anemia. You can use the ESR to help differentiate iron deficiency anemia (low esr) from inflammatory anemias (high esr). Both categories of anemias can present with the similar indices, so the ESR can help differentiate the two.

Related Questions

Blood test showed, ESR and RDW levels slightly high, and hematocrit level decreased slightly but no iron deficiency, suffering from dizziness. Scary?

POT and Minerals. A twenties female taking Aldactone (spironolactone) and who has dizziness needs blood mineral and thyroid tests. If these are normal a mild case of postural orthostatic tachycardia syndrome (pots) becomes of concern. I have seen pots problem in women with joint hypermobility syndrome (jhs), and generalized musculoskeletal deconditioning seems etiologic. See an osteopath. Read more...