Principles of Serology

Unit II - Immunodiagnostics

Define serology:

study of fluid components in the blood, especially antibodies

What are the components of plasma?

water, plasma proteins, nutrients, waste, gases, electrolytes, hormones, coagulation factors

What is not included in serum?

coagulation factors

What collection tubes do not contain anticoagulants?

plain tubes (serum) and GEL tubes (serum separator)

If testing is delayed, how should serum be stored?

between 2-8C for up to 72 hours, or frozen at -20C or below

How is complement inactivated?

heating the sample to 56C for 30 minutes

Why does complement inactivated?

complement may interfere with certain test results

Define dilution:

the process of decreasing the concentration of a solute in a solution by adding more diluent

Define solute:

the substance that is dissolved in a solution

Define diluent:

the liquid (water, buffer, etc) being added

What is the dilution formula?

C1V1 = C2V2

Diagnostic sensitivity is…

how good the test is at detecting disease when it’s present

Diagnostic Specificity is…

how good the test is at ruling our disease when it’s absent

Positive Predictive Value (PPV) and Negative Predictive Value (NPV) demonstrate…

how likely a positive or negative test reflects the patient’s true status

How is diagnostic sensitivity determined?

true positives / (true positives + false negatives)

How is diagnostic specificity determined?

true negatives / (true negatives + false positives)

“SnOUT”:

a highly sensitive test helps us rule disease out

“SpIN”:

a highly specific test helps rule disease in

True or False: there is a perfect test

false

What happens to specificity if sensitivity is increased?

more true positives are caught, but there are more false positives (lower specificity)

What happens to sensitivity if specificity is increased?

less false positives, but there is a risk of missing more true cases (lower sensitivity)

High sensitivity…

is like a big fishing net, catching nearly all the fish (few false negatives) but can also scoop up things you don’t want (more false positives)

High specificity…

is like using a targeted lure/bait designed to catch a specific type of fish (few false positives) but only the fish that bite (more false negatives)

How is positive predictive value (PPV) determined?

true positives / (true positives + false positives)

Define PPV:

probability that a person with a positive screening test actually has the disease

How is negative predictive value (NPV) determined?

true negatives / (true negatives + false negatives)

Define NPV:

probability that a person with a negative screening test does not have the disease