Introduction: Laboratory

Introduction to Hematology

You should know a little bit about how to approach a patient with a suspected hematologic disorder. These general tips will help you build a framework for the in-depth discussions of specific diseases we will cover later...and they will help you as you begin to take care of patients in your third and fourth years of medical school.

Clinical approach to patients with hematologic disorders.

What are some of the tip-offs that your patient may have a hematologic disorder? How should you direct your physical exam if you are concerned about a hematologic disorder?

Laboratory approach to patients with hematologic disorders.

The complete blood count (CBC) is a collection of tests which evaluates the three kinds of cells in the blood: red cells, white cells, and platelets. Some of the indices (indicated here in red) are used more frequently than others.

RBC (red blood cell count) = total number of red blood cells in blood

Normal range = M 4.5-6.0 x 10 /L, F 3.8-5.2 x 10 /L

Hemoglobin (Hgb) = concentration of hemoglobin in blood

Normal range = M 13-18 g/dL; F 12-16 g/dL

Hematocrit (Hct) = volume of “packed” red blood cells.

Calculated by machine (MCV x RBC)

Rough guideline: Hct should = Hgb x 3).

Normal range = M 40-52%, F 35-47%

MCV (mean red blood cell volume)

Normal range = 80-100 fL (1 fL = 10 L)

MCH (mean cell Hgb) = weight of Hgb in the average red blood cell

Normal range = 26-34 pg (1 pg = 10 g)

MCHC (mean cell Hgb concentration) = concentration of Hgb in the average red

blood cell. Calculated by machine (Hgb/Hct).

Normal range = 32-36 g/dL

RDW (red cell distribution width) = standard deviation of the MCV.

Tells you how much the red blood cells differ from each other in size.

If they are all pretty similar in size: low RDW.

If some are tiny and some are huge: high RDW.)

Normal range = 12-13.5%

WBC (white blood cell count) = total number of leukocytes in blood

Normal range = Adult: 4.5-11 x 10 /L

Child: 5.0-17.0 x 10 /L (range differs according to age)

Differential = percentages of each cell type in blood

Normal ranges:

Adults

Children

Neutrophils 45-75% 20-55%

Lymphocytes 20-50% 25-75%

Monocytes 1-8% 0-10%

Eosinophils 0-6% 0-6%

Basophils 0-1% 0-6%

Platelet count (Plt) = total number of platelets in blood

Normal range = 150-450 x 10 /L

MPV (mean platelet volume)

Normal range depends on the platelet count!

Normally, if the platelet count falls, the body compensates a little by

trying to make bigger platelets.

How to look at a blood smear.

What are the three big things to look at when faced with a blood smear?

In each of these three parts, what characteristics should you evaluate?