A reduction in the total iron content in the human body is called iron deficiency. Iron is essential for several metabolic processes as well as erythropoiesis. Iron deficiency can develop insidiously leading to increased fatigability, lassitude, poor immunity, irritability, and iron deficiency anemia. Causes of iron deficiency are several and early identification is the key to managing the condition.
Iron deficiency (ID) is more frequent than ID anemia  and between 2 -5% of postmenopausal women and adult men suffer from ID anemia  . ID develops when the iron intake falls short of the iron requirements of the body (pregnancy, adolescence) or when the output of iron exceeds the intake (gastrointestinal bleeding).
ID often presents insidiously with non-specific symptoms like tiredness, poor immunity to infections and low exercise tolerance. The incidence of ID is more common in premenopausal women due to menstrual blood loss while in pregnancy, adolescence and during breastfeeding, ID is due to increased requirements of iron. ID can lead to increased fatigability, especially in women   . Athletes are also at risk of iron deficiency as studies have shown urinary loss of iron following repeated minor intravascular hemolysis  . ID can lead to anemia which can present with koilonychia, atrophic glossitis, fissured tongue, angular cheilitis, pica, pallor, decreased intellectual abilities, dyspnea, hepatosplenomegaly (in hemolytic anemias), high output cardiac failure, and recurrent upper respiratory tract as well as other infections. Chronic diseases like celiac disease, chronic renal failure, cirrhosis and even cancers can be associated with ID with patients manifesting symptoms and signs of these conditions. Gastrointestinal tract bleeding is another potential presenting feature in individuals taking non-steroidal anti-inflammatory drugs (NSAIDs) over long periods of time or in those with malignancies of the gastrointestinal tract.
ID can develop insidiously with or without anemia. Therefore early diagnosis of the condition is difficult. In all patients, a detailed history of symptoms, history of chronic intake of NSAIDS and blood loss in urine or stools or excessive menstrual blood loss should be obtained. NSAID enteropathy is associated with significant amounts of blood loss . A thorough physical examination to identify features of ID and ID anemia like pallor, koilonychia, glossitis and even high output cardiac failure should be performed.
Routine laboratory tests like complete blood count, hemoglobin levels, hematocrit, urinalysis for hematuria and stool test for occult blood as well as other tests like liver enzymes, renal function tests, echocardiography are indicated depending on the history and physical examination findings. Specific tests for iron deficiency detection include serum ferritin, serum iron, and transferrin saturation.
Tests to detect the cause of the ID include celiac disease serology, gastroscopy and colonoscopy . Repeated endoscopies or capsule endoscopies may be necessary to detect persistent ID .