Why Blood Loss From Sites other than Gastrointestinal Tract Rarely Causes Iron Deficiency?

A 55 year old man presented with breathlessness on climbing stairs. He saw his family physician who found the patient to be pale. The patient was advised a complete haemogram. He was found to be anaemic and was asked to see a haematologist.

The haemogram showed an haemoglobin of 3.1 g/dL with an MCV of 63fl. The WBC count was 5600 with 65% neutrophils, 30% lymphocyte, 3% monocytes and 2% eosinophils. The platelet count was 475 X 1009/L. The reticulocyte count was 1%.

The serum iron was 15μg/dL and the total iron binding capacity 450μg/dL and a transferrin saturation of 3.3%. The serum ferritin was 8ng/ml. A diagnosis of iron deficiency anaemia was made he was initiated on oral iron which he responded to. 

Iron deficiency is common in 

  1. Growing children because of dietary deficiency
  2. Women in the reproductive age group because of menstrual blood losses and iron depletion because of foetal transfer of iron during pregnancy.

When iron deficiency occurs in a well nourished man or a well nourished post-menopausal women it is invariably due to a gstrointestinal blood loss. Why is gastrointestinal blood loss different from other forms of blood loss?

Bleeding is an alarming symptom. It is rare for a person to ignore bleeding. Bleeding from the respiratory system, urinary system and skin is apparent and alarming. Such bleeding prompts the patient to promptly seek medical attention. Gastrointestinal bleeding may be of three types. The patient may pass fresh blood, the patient may have malaena or the patient may have occult bleeding. Passage of fresh blood with stools is a symptom of a lower gastrointestinal pathology. Such patients seek attention early and usually do not become anaemia. Haemorrhoids is an exception not because the patient does not realise that there is bleeding but because the patient may ignore the bleeding because he/she attributed it to a known cause. Some patients may not realise the significance of malaena and may present only when anaemic. A patient may loose upto  30ml of blood without a change in the consistency or colour of stools. Such patients present with iron deficiency anaemia. As the anaemia has a gradual onset the it may become severe and yet not cause symptoms. 

The diagnosis of anaemia is complete only if the type of anaemia and the cause of anaemia are determined. A rule of thumb is that unexplained iron deficiency anaemia in a man or a postmenopausal woman should be considered to be due to a occult gastrointestinal blood loss unless proven otherwise. The importance of this practice can not be overemphasised. A colon cancer develops in an adenoma. Completing the evaluation of an iron deficency anaemia provides an opportunity to diagnose a colorectal cancer either in the premalignment stage or when the disease has a limited extent. Not perusing the diagnostic evaluation of an iron deficiency anaemia to completion may close the window of early diagnosis of gastrointestinal cancer.

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