Pallor is almost invariably caused by anemia and is best analyzed with the application of pathophysiology. Anemia may be caused by decreased production of blood, increased destruction of blood, or loss of blood. Decreased production results from poor nutrition particularly, poor absorption or intake of B12 (pernicious anemia), iron (iron deficiency anemia), and folic acid (malabsorption syndrome). It may also result from suppressed bone marrow (aplastic anemia) or infiltrated bone marrow (leukemia or metastatic carcinoma). Increased destruction is caused by hemolysis from intrinsic defects in the red cells (e.g., sickle cell anemia and thalassemia) or extrinsic defects in the circulation (autoimmune hemolytic anemia of many disorders). Blood loss may result from peptic ulcers and carcinomas of the GI tract, excessive menstruation or metrorrhagia from tumors of the uterus, or dysfunctional uterine bleeding. These are the principal causes of anemia, but the reader will be able to think of several more. What is important here is to have a systematic method to recall them.


PALLOR OF THE FACE, NAILS, OR CONJUNCTIVA

If anemia is ruled out, the less frequent causes of pallor should be considered. Shock, CHF, and arteriosclerosis cause pallor by poor circulation of blood to the skin. Patients who have hypertension may be pale from reflex vasomotor spasms of the arterioles supplying the skin. Aortic regurgitation and stenosis, as well as mitral stenosis, cause pallor for the same reasons but the malar flush of mitral stenosis may negate this.
The reason that tuberculosis, rheumatoid arthritis, carcinomatosis, and glomerulonephritis cause pallor even when their victims are not anemic or hypertensive is not known.

Approach to the Diagnosis

The approach to the diagnosis of pallor is obviously to check for anemia first; then examination for the other chronic disorders may be carried out. Chest x-ray, ECG, sedimentation rate, and a check for rheumatoid factor are all appropriate in specific cases

Other Useful Tests

CBC (anemia)
Sedimentation rate (chronic infection)
Chemistry panel (anemia of liver and kidney disease)
Serum B12 level (pernicious anemia)
Serum folic acid level (folic acid deficiency)
Serum iron and ferritin levels (iron deficiency anemia)
Stool for occult blood (GI bleeding)
Stool for ova and parasites (anemia due to parasite infestation)
Serum haptoglobins (hemolytic anemia)
ANA analysis (collagen disease)
Bone marrow examination (aplastic anemia)

Source:
Differential Diagnosis in Primary Care, Lippincott Williams & Wilkins

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