What does a lab tech do?

Laboratory Technologists fly well under the radar. Thanks to shows like House, a lot of people don't know what we do, or even that we exist at all! A doctor in one of these medical dramas may process the patient's sample themselves, but this is not usually the case. So what does happen when a sample leaves the hands of the doctor or nurse?


The department I find most interesting is Microbiology, so I'll try and give an idea of what we do there.

Example

A patient in ICU, with a central venous catheter, develops an elevated temperature. One of things the physician will naturally be suspicious of is bacteremia, or a blood infection. This can be quite serious, especially in children and in immunocompromised patients (patients who have a weak immune system). So the doctor orders that a blood culture be drawn, and laboratory staff receive this order and perform the collection. Usually two vials are collected: one supports the growth of aerobic bacteria, the other anaerobic bacteria (bacteria that require an environment without oxygen in order to thrive.)

These vials are then placed in an incubator. Something like this one (though this looks like a slighter older model):

After a few hours, if bacteria grow, the vial will alarm as being positive. The machine detects increased levels of CO2 that are produced by bacteria present in the vial. A technologist removes the positive vial, and places a drop of the blood onto a slide, to confirm the presence on bacteria under a microscope. A majority of the times either "gram-negative rods" or "gram positive cocci" are seen.

Here is a gram-negative rod:

For our example, lets say that gram-positive cocci are seen:

These cocci are in grape-like clusters, which is indicative of Stapylococcus species, but more must be done to determine which species it is exactly. To do this blood from the positive vial is streaked onto agar plates. There are various kinds of plates containing nutrients that either encourage or inhibit the growth of different types of bacteria. The most common plate is the Blood Agar Plate (BAP), and this one is loved by almost all bacteria, with a few exceptions:

So, the plates are streaked and then incubated at 35°C overnight. They like it toasty.
This is what grows:

Now the technologist has a pretty good idea of what species it is. Staphylococcus aureus hemolyzes the blood agar plate; that is, the bacteria causes the red blood cells in the agar to break apart, and this creates a clearing in the agar around the colony. In the above picture you can see a light shining through the plate where the blood has been hemolyzed.

Some other tests will be done to confirm that this is indeed what it is. Placing S. aureus in a tube of rabbit serum, for example, will cause the serum to coagulate due to the action of a coagulase enzyme that this organism produces. It is the only Staph species to produce this enzyme (with rare exceptions).

Then the bacteria will be exposed to several different antibiotics to determine what drugs it is sensitive to, and whether it is unexpectedly resistant to any. MRSA, or Methicillin Resistant Staph Aureus, is a serious problem as they will be resistant to penicillin and many other first-line drugs. This will mean having to give the patient much harsher antibiotics.

Hopefully this explains a little of what is done in the microbiology laboratory. Maybe when the geek-spirits possess me once more, I will detail what happens in the lab when someone needs a blood transfusion.