Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1190 page)

   Marked leukocytosis marginally increases the RBC count.

   Inappropriate blood collection is a major source of preanalytic errors. For instance, inappropriate filling of test tube results in excess anticoagulant, thereby diluting the blood and decreasing the red cell parameters.

   Very low temperatures may lyse the red cells. Anticoagulated blood may be stored at 4°C for 24 hours, but beyond this interval, the results become increasingly altered.

RED CELL DISTRIBUTION WIDTH (RDW)
*

   Definition

   RDW is a coefficient of variation of the distribution of individual RBC volume.

   
Normal range:
12.1–14 fL.

   Use

   An elevation in RDW is useful in drawing attention to anisocytosis, a marker for various anemias.

   Interpretation

   The RDW is particularly helpful in separating iron deficiency anemia (high RDW, normal to low MCV) from β-thalassemia trait (normal RDW, low MCV).

   Increased RDW is also useful in identifying red cell fragmentation, agglutination, or dimorphic cell populations.

   Limitations

   Very high WBC, numerous large platelets, and autoagglutination result in falsely elevated RDW.