Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1192 page)

RETICULOCYTES
^†

   Definition

   Reticulocytes are immature RBC without nuclei. The reticulocyte count provides an estimate of the rate of red cell production. To visualize the reticulum-like RNA and count reticulocytes as a separate group of RBC, a special stain is required. The reticulocytes can be counted manually (at the microscope) and reported as percent per 100 RBC, or by automated counters.

   
Normal range:
0.3–2.3/100 RBCs with automated counters. However, this varies to some extent in the manual methodology. An absolute reticulocyte count or reticulocyte production index is more helpful than the percentage, and this can be calculated from the hematologic data.

   Interpretation

Causes of Increased Reticulocytes

   Reticulocytosis: Enhanced red cell production most marked in hemolytic anemias or during bone marrow regeneration

Causes of Decreased Reticulocytes

   Conditions with inadequate or ineffective hematopoiesis, despite the presence of anemia

   Limitations

   The manual counts result in great variability, being operator dependent. The automated counters provide better precision. Erythrocyte inclusions, other than the true reticulum, may falsely increase the reticulocyte count. Similar errors occur in sickle cell anemia and sickle/C hemoglobinopathies.

REVERSE T
₃
(rT
₃
), TRIIODOTHYRONINE, REVERSE

   Definition

   Hormonally inactive isomer of T
₃
.

   
Normal range:

   Birth to 6 days: 600–2,500 pg/mL

   ≥7 days: 90–350 pg/mL