List of  Lessons

Lesson 9-1 Diagnosing Anemia

INTRODUCTION

Physicians and clinical laboratory scientists counted RBC’s in measured volumes to detect anemia or polycythemia. Anemia means loss of oxygen-carrying capacity and is often reflected in a reduced RBC count. Polycythemia means an increased RBC count related to increase body RBC mass.

Major laboratory manifestations of anemia:

• Decreased hemoglobin (Hgb) concentration.
• Reduced packed cell volume hematocrit (Hct).
• Decreased number of RBCs/L.

Laboratory testing procedures for assessing anemia:

• Hemoglobin and hematocrit - most widely used.
• Red blood cell count.
• Red blood cell indices:
• Calculations used to define the size of and hemoglobin concentration within red blood cells.
• May be calculated manually but are usually calculated by automated instruments.
• RBC indices, combined with an examination of the RBCs on a stained smear, tell the examiner whether the RBCs are normocytic, microcytic, macrocytic (size related), and normochromic, or hypochromic (Hgb content related).

3-2. ERYTHROCYTE INDICES

Mean Corpuscular Volume (MCV):

1. Indicates the average volume of the RBCs in femtoliters (fL).

2. Expressed in SI units as femtoliter (fL; 1 fL = 10–15 L).
3. Formally expressed as microliter (μ3L).
4. Formula:

1. Example

1. Reference range: 80 to 100 fL.

Mean Corpuscular Hemoglobin (MCH):

1. Indicates the average weight (content) of hemoglobin in a RBC.
2. Expressed in SI units as picograms (pg; 1 pg = 10-12 g).
3. Formula

1. Example: RBC = 4.2 x 1012 RBCs/L

1. Reference range: 27 to 31 pg.

Mean Corpuscular Hemoglobin (MCH):

(1) Indicates the average weight (content) of hemoglobin in a RBC.

(2) Expressed in SI units as picograms (pg; 1 pg = 10-12 g).

(3) Formula:

(4) Example:

(5) Reference range: 27 to 31 pg.

Mean Corpuscular Hemoglobin Concentration (MCHC):

1. Calculated from Hemoglobin and Hematocrit and is an expression of the average concentration of hemoglobin in the RBC.
2. Expressed in SI units as g/dL.
3. Formerly expressed as percent (%).
4. Formula:

1. Example:

1. Reference range: 31 to 36 g/dL (or %).

3-3. MORPHOLOGY OF RBC’S ASSOCIATED WITH VARYING INDICES

MCV and Expected RBC Morphology.

• Elevated MCV (100 fL) – Macrocytic RBCs.

• Normal MCV (80 – 100 fL) – Normocytic RBCs.

• Decreased MCV ( 80 fL) – Microcytic RBCs.

MCH and Expected RBC Morphology.

• Elevated MCH (31 pg) - usually macrocytic/normochromic RBCs.

• Normal MCH (27 – 31 pg) - usually normocytic/normochromic RBCs.

• Decreased MCH (27 pg) - variable macrocytic to microcytic / normochromic to hypochromic RBCs.

 NOTE: MCH rarely used alone; results should be correlated with MCV and MCHC.

MCHC and Expected RBC Morphology.

• Elevated MCHC (36 g/dL) – Normochromic never use the misnomer “hyperchromic”:

• Hereditary spherocytosis.

• Usually MCHC does not rise above 37 g/dL - at 37 g/dL, hemoglobin becomes gel-like and at higher concentrations crystallization may occur.

• If greater than 38 g/dL, check specimen for cold agglutinins and lipemia. Lipemia may cause falsely elevated hemoglobin values, thus elevating the MCHC calculations.

• Normal MCHC (31 – 36 g/dL) -- normochromic RBCs.

• Decreased MCHC ( 31 g/dL) -- hypochromic RBCs.
 NOTE: RBC color intensity is directly proportional to the cell's hemoglobin concentration. When reviewing a peripheral smear, the color of the RBCs should correspond to the MCHC value.