Pathology > Basic Hematology > Red Cell Disorders > Introduction

Introduction

The Red Cell Disorders unit is organized mechanistically or physiologically into three major sections: 1) Increased RBC Destruction, 2) Decreased RBC Production, and 3) Blood Loss.

The Increased RBC Destruction or Hemolytic anemia section includes anemias secondary to membrane disorders, enzyme deficiencies, abnormalities of hemoglobin synthesis, antibody mediated destruction, and mechanical trauma.

The Decreased RBC Production section includes anemias secondary to decreased hemoglobin synthesis as in the microcytic anemias of iron deficiency and thalessemia, and the abnormalities of DNA synthesis as in the megaloblastic anemias, abnormalities of proliferation, and failure of differentiation.

The final section is on anemia secondary to Blood loss. Certain proliferative disorders of red cells are considered in the unit on proliferative disorders of white cells.

What is anemia? First, anemia is not a specific disease. Anemia is the finding of too few red blood cells or an abnormally low hematocrit or too little hemoglobin. Symptoms of anemia include fatigue, weakness, syncope, decreased appetite and occasionally chest pain, shock or congestive heart failure.

Physical signs of anemia are manifest by pallor of the skin, palmar creases, nail beds, and mucous membranes (conjunctiva). In severe anemia the heart rate may increase. Decreased blood pressure, often orthostatic may be present.

It is critical to determine the cause of the anemia. Anemia may result from 1) Increased RBC destruction, 2) Decreased RBC production, or 3) blood loss. A careful patient history for evidence of blood loss should include questions regarding gastrointestinal bleeding, hematemasis (vomiting blood), melena (black stool), or hematochezia (red blood in feces). Hemoptysis (coughing up blood), epistaxis (nosebleed), and hematuria (blood in urine) must also be investigated. Menstrual blood loss should be estimated and questions asked regarding menorrhagia (excessive bleeding) or metrorrhagia (irregular bleeding).

 

The quaiac test for occult blood is based on detection of endogenous peroxidase in RBCs.

Hemoglobin and myoglobin of meat and fish can give false + results. Vitamin C can cause a false negative result. Why?

 

Other data from the medical history may help in determining the cause of the anemia. For instance, papillar atrophy of the tongue and angular stomatitis are common in megaloblastic anemia secondary to Vitamin B12 deficiency. Peripheral neuropathy and paresthesias may accompany Vitamin B12 deficiency. History of a malignancy and the record of treatment are important. A review of all medications is also indicated.

Dietary questions may be important in assessing anemias of childhood or the elderly. Other questions regarding the patient's age and sex; their habits regarding exercise, alcohol and smoking should also be considered when investigating evidence of anemia.

A family history of anemia, early onset of cholelithiasis (bilirubin), or jaundice might suggest a hemolytic anemia or possibly hemoglobin synthetic disorder.

 

Of course you must check the measured blood parameters. The Hematocrit (Hct); Hemoglobin (Hgb), and Mean Corpuscular Volume (MCV) are the most useful parameters of the Complete Blood Count (CBC).

Most important is examination of a Wright's stained peripheral blood smear by the physician.

From this one can estimate the Hct; judge the size and the degree of size variability (anisocytosis); look for changes in RBC shape (piokilocytosis), and judge the RBC chromicity.

Now you are ready to review the anemias in more depth, beginning with those caused by increased RBC destruction, then by decreased RBC production, and finally by loss of blood.

In the next section we begin a discussion of anemias caused by increased RBC destruction.

 

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