Understanding Basic Lab Values

Understanding Lab Values

Diagnostic tests often drive the direction of patient care. Some research shows 25% to 30% of the data used to drive treatment decisions comes from a patient’s lab values. Understanding lab value ranges and their significance can help you better understand what’s going on with your patient.

Laboratory tests refer to studies performed on body tissues like urine, blood, feces, cerebral spinal fluid, etc. These tests are used to detect abnormal values outside their normal reference range. These tests can be further categorized into hematology, microbiology, pathology, chemistry, and serology. Although set values exist to establish a normal range (established references) these normal values vary with age, sex, and even altitude.

Quick Definition

Quantitative vs. Qualitative

Lab tests are either quantitative, referring to a numeric value (like a hemoglobin value of 11.2) or qualitative (yes/no, like a pregnancy test). The precision of a test depends on both the sensitivity and specificity of the test.

Complete Blood Count (CBC)

A CBC is the most common hematology test (blood test). It looks at a number of specific components of a patients blood. Variance outside the normal references range for each of these components can signal various disease states and homeostatic imbalances within a patient. Components of the CBC include:

Hemoglobin (the protein molecule in red blood cells that carries oxygen)

Normal Values:

Men: 13.0 to 18.0 g/dl Women: 12 – 16 g/dl

High hemoglobin values can be caused by things like a history of smoking, living at high altitude

Low hemoglobin values can be caused by anemia, blood loss, over-hydration

Hematocrit (percentage of red blood cells in plasma)

Normal Values:

Men: 37% to 49% Women: 36% to 46%

High hematocrit values can be caused by things like dehydration and polycythemia.

Low hematocrit values can be caused by over-hydration, anemia, and blood loss


White Blood Cells (WBC)

White blood cells are measured by the number of white blood cells in one cubic millimeter of blood

Normal Values:

4500 to 11000 /mm3

High WBC values indicate things like infection, leukemia, and chronic steroid use

Low values indicate immunodeficiency. A patient with a severe infection may also present with a low WBC if they have used up most of their WBC fighting the infection (a late sign)

Leukemia vs. Infection: WBC values will usually be elevated to 20000 / mm3 or so when a patient is suffering from an acute infection. In cases of Leukemia, values can extend to WBC counts of 50000 + / mm3


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