Basics of blood components and analysis

What are the two major components of blood?

Fluid (plasma) and cells

What are the three types of cellular components in blood?

Red blood cells (RBCs), white blood cells (WBCs), and platelets.

What is the function of red blood cells (erythrocytes)?

Transport of gases (O2 and CO2).

What is the function of white blood cells (leukocytes)?

Defense and immunity: destruction of microorganisms and removal of dead or damaged tissues.

What is the function of platelets (thrombocytes in non-mammals)?

Component of the clotting system (stop bleeding).

What is plasma?

The supernatant of whole blood (blood collected in a tube with anticoagulant and centrifuged).

What is serum?

The supernatant of clotted blood (blood collected in a tube without anticoagulant and centrifuged).

What is the main difference between plasma and serum?

Plasma contains clotting factors (e.g., fibrinogen); serum does not because the blood has clottec

What percentage of plasma is water?

50%.

What percentage of plasma is proteins?

4%.

What are the three main types of plasma proteins, and what percentage of total protein does each make up?

Albumin (60%), Globulins (36%), and Fibrinogen (4%).

What is the most abundant plasma protein?

Albumin.

What is the function of albumin in the blood?

It is mainly responsible for oncotic pressure (pulls water into the circulatory system).

Where is albumin produced?

The liver.

What is the purpose of a tube with no anticoagulant (red top)?

To yield serum after clotting and centrifugation.

Name three common anticoagulants used in blood collection tubes.

Citrate, Heparin, and EDTA.

What does a CBC (Complete Blood Count) measure

Cellular analysis: count of cellular elements, cell classification, and morphology.

What does clinical chemistry test?

Quantification of a chemical substance on serum or plasma.

What does coagulation testing measure?

Whole blood assays for platelet function and clotting factor function.

What are the three main categories of error that affect the quality of laboratory results?

Preanalytical error, analytical error, and postanalytical error.

What is a preanalytical error?

An error that occurs prior to analyzing the sample.

What are the three subcategories of preanalytical error?

Patient factors (e.g., non-fasted), collection factors (e.g., venipuncture technique, anticoagulant, hemolysis), and handling factors (e.g., temperature, duration to processing).

What is an analytical error?

An error that occurs during analysis (e.g., method, analyzer equipment, reagents, technique, quality control).

What is a postanalytical error?

An error that occurs after analysis (e.g., transcriptional or readability errors).

Which type of error is the most common?

Preanalytical error.

What is accuracy?

How close a measurement is to the true or accepted value.

What is precision?

How close repeated measurements are to each other.

What is random error?

Unpredictable variations that cause measurements to differ each time

What does random error primarily affect?

Precision (not necessarily accuracy).

What is systematic error?

A consistent bias that shifts all measurements in one direction.

What does systematic error primarily affect?

Accuracy (but may not affect precision).

What is an example of systematic error?

A scale that is always 2 grams too high.

What does the coefficient of variation (CV) quantify?

The degree of test imprecision; it quantifies precision in blood work.

What is the formula for CV%?

(Standard Deviation / Mean) x 100.

What does a low CV% indicate?

Greater precision (more confidence that a change between test results is real).

What does a high CV% indicate?

Less precision (small changes in a value may be due to analytical variation rather than biological change).

What is analytical variation?

Differences in test results caused by the measurement process (pre-analytic, analytic, or post-analytic error, or test imprecision).

What is biologic change?

True physiological alterations in the analyte concentration within the patient over time (due to development or resolution of pathology).

What is a reference interval (RI)?

A set of expectations for results you expect to find in healthy animals for a given analyte; presented as a range with upper and lower limits.

How are reference intervals constructed?

A set of healthy animals get blood work; statistics are applied; for gaussian distribution, the mean +/- 2 standard deviations becomes the RI.

What percentage of normal animals should have an analyte value within the RI?

95% (19 out of 20).

What is the formula for the chance of a normal animal being outside the RI?

100 x (1 - 0.95^n), where n = number of analytes.

For 20 analytes run on a patient, what is the chance that at least 1 analyte is outside the RI and the patient is still normal?

65%.

Can a patient have a result within the RI and still have pathology?

yes