Polychromasia is a finding on a routine blood test describing the presence of abnormally colored red blood cells (RBCs) when viewed under a microscope. The term translates from Greek to mean “many colors,” reflecting the variation seen on a peripheral blood smear. This observation indicates that circulating RBCs are not the uniform salmon-pink color expected of mature cells. Instead, some cells display a bluish, purplish, or grayish-blue tint. Polychromasia is not a diagnosis itself, but it serves as an important clue that the body is rapidly producing new red blood cells.
The Distinctive Appearance of Polychromatic Red Blood Cells
The color variation observed in polychromasia is a direct consequence of the red blood cells’ stage of maturity. Mature red blood cells are predominantly filled with hemoglobin, the oxygen-carrying protein, which is responsible for their characteristic pink or salmon-red color when stained. In contrast, polychromatic cells are actually immature red blood cells, known as reticulocytes, that have been released prematurely from the bone marrow.
These immature cells retain residual components from their development process, most notably ribosomal ribonucleic acid (RNA). The specialized laboratory stain reacts differently with this RNA compared to the hemoglobin. This reaction causes the reticulocytes to take on a bluish or purplish-gray appearance, blending the red of the hemoglobin with the blue of the RNA content.
Polychromatic cells are generally larger than the surrounding mature red blood cells, which is another identifying feature. The presence of these larger, bluish cells suggests that the bone marrow is working overtime. The marrow is pushing out red blood cells before they have completed their final maturation steps, indicating a high demand for oxygen-carrying capacity.
Conditions That Trigger Polychromasia
The underlying reason for polychromasia is always a physiological state that forces the bone marrow to accelerate its production of red blood cells. This accelerated production leads to the early release of reticulocytes into the circulation. One common trigger is acute blood loss, such as from trauma or significant internal bleeding. The body responds immediately to the sudden drop in red cell volume by ramping up output to replace the lost cells.
Polychromasia is also a common finding in various forms of hemolytic anemia. In this group of conditions, red blood cells are destroyed faster than their normal lifespan of about 120 days. The bone marrow attempts to compensate for this rapid destruction by releasing immature cells to maintain a functional red blood cell count. Conditions such as sickle cell disease, thalassemia, or autoimmune destruction of red cells fall into this category.
A third scenario is during an effective treatment response to a nutritional deficiency. If a person has anemia caused by a lack of iron, vitamin B12, or folate, the body cannot manufacture red blood cells efficiently. Once the patient receives the necessary supplementation, the bone marrow responds with a burst of new red blood cell production. This surge results in a temporary, but positive, finding of polychromasia as the patient begins to recover.
Clinical Significance and Follow-Up Testing
The discovery of polychromasia on a peripheral blood smear signals to the healthcare provider that the bone marrow is actively responding to a stimulus. The degree of polychromasia is typically graded by laboratory technicians as mild, moderate, or marked, offering an initial assessment of the marrow’s activity. A marked increase in these bluish cells suggests a significant demand for new red blood cells.
This finding nearly always prompts a specific follow-up test called a Reticulocyte Count. While polychromasia is a qualitative observation made during microscopic review, the reticulocyte count provides a precise percentage of these immature cells in the bloodstream. A high reticulocyte count confirms the bone marrow’s hyperactivity, indicating an appropriate response to conditions like blood loss or hemolysis.
Conversely, an unexpected finding of polychromasia with a low reticulocyte count can suggest an underlying issue with the bone marrow itself. The ultimate step in patient management is to correlate the polychromasia with other blood test results and the patient’s medical history to pinpoint the exact condition driving the accelerated cell production. This process determines whether the finding represents a healthy compensatory mechanism or a deeper underlying pathology.