SCV 213 Lab machines and blood tubes

What is a centrifuge used for?

It spins tubes fast to separate a sample by weight. The heavy stuff (cells) sinks to the bottom as sediment. The lighter liquid (serum or plasma) stays on top as supernatant.

What are the two main centrifuge types in vet clinics?

Microhematocrit centrifuges only hold small capillary tubes and need an inner lid before spinning. Clinical centrifuges hold regular blood tubes and come in fixed-angle or swing-arm styles.

Fixed angle centrifuge: pros and cons?

Tubes sit at a fixed angle (about 52 degrees) and it spins faster than a swing arm. It can't hold conical tubes and usually only fits one tube size.

Swing arm centrifuge: pros and cons?

Tube holders swing outward while spinning so tubes end up straight up and down. It works for blood and conical tubes, but it's bigger and heat buildup can damage samples.

Why must centrifuge tubes be counterbalanced?

You need a tube of equal weight and volume placed directly across from your sample tube. This stops wobbling, keeps liquid from spilling, and protects the machine.

What happens if you spin a sample too long or too fast?

Cells can rupture and crystals can be destroyed. This changes how the sample looks under the microscope, so always follow the correct time and speed.

What happens if you spin a sample too short or too slow?

The sample won't separate fully into its layers. You won't get a clean split between cells and liquid.

What is a refractometer used for?

It measures how much light bends when passing through a liquid, which shows the concentration of solids. Vets use it to check urine specific gravity and plasma protein.

How do you calibrate a refractometer?

Place a drop of distilled water on the prism and look through the eyepiece. It should read 1.000 on the specific gravity scale; if not, turn the calibration screw.

What are the two scales on a refractometer?

One scale reads specific gravity (for urine), and the other reads total protein/solids (for serum or plasma). Dogs and cats have separate specific gravity scales since normal values differ.

What is a compound light microscope?

It's the standard microscope used in vet clinics. It uses two sets of lenses (ocular and objective) plus a light source to magnify blood cells, parasites, and more.

What are the objective lens magnifications on a microscope?

4x is scanning power, 10x is low power, 40x is high power dry, and 100x is oil immersion. Never put oil on the 4x, 10x, or 40x lenses, only the 100x.

How do you calculate total magnification?

Multiply the ocular lens power by the objective lens power. Example: a 10x eyepiece times a 40x objective equals 400x total magnification.

What is the ocular lens?

It's the eyepiece lens you look through, usually 10x magnification. Microscopes can be monocular (one eyepiece) or binocular (two eyepieces).

Name the main parts of a microscope.

Ocular lens (eyepiece), objective lenses (on the nosepiece), stage (holds the slide), and coarse/fine focus knobs. The condenser and diaphragm below the stage control the light.

What do the condenser and diaphragm do?

The condenser focuses light from below onto your slide. The diaphragm opens and closes to control how much light gets through.

How should you handle the 40x and 100x lenses?

Once on 40x or 100x, only use the fine focus knob, never the coarse knob, or you could crack the slide. Never let the dry 40x lens touch oil.

How do you use the 100x oil immersion lens?

First focus on your area using 4x or 10x, then move to 40x and refocus. Add a drop of oil, rotate the 100x lens into the oil, and use only the fine focus knob.

How should you care for a microscope after use?

Clean the lenses with lens paper, wipe off any oil or specimen from the stage, turn off the light, and cover it. Always carry it with two hands.

What is a stage micrometer vs an ocular micrometer?

An ocular micrometer is a measuring scale built into the eyepiece, used to size things like parasite eggs. A stage micrometer is a special slide used to calibrate that scale, usually only done once.

Name other types of microscopes besides compound light.

Electron microscopes use a beam of electrons for extreme close-up detail. Phase-contrast, fluorescent, and dark-field microscopes are found in research or reference labs to highlight hard-to-see cells.

What's the difference between whole blood, plasma, and serum?

Whole blood is straight from the vein, unprocessed. Plasma is the liquid part after blood is mixed with an anticoagulant so it doesn't clot. Serum is the liquid left after blood clots and uses up its clotting proteins.

Plain Red Top Tube (RTT): what's it for?

This tube has no additives, so blood clots inside it and produces serum. It's used for endocrine testing, cultures, and drug testing like phenobarbital.

Serum Separator Tube (SST) / Tiger Top: what's it for?

This tube has a silicone gel that separates the clot from the serum after spinning. It's used for chemistry panels but NOT for drug testing or glucose, since the gel can interfere.

Lavender Top Tube (LTT): what's it for?

This tube contains EDTA, which stops clotting by binding calcium. It's the go-to tube for CBCs and blood cell counts because it protects cell shape.

Light Gray Top Tube: what's it for?

This tube contains oxalate, which stops clotting by binding calcium. It's used for coagulation testing, but not for chemistry panels or potassium testing.

Dark Gray Top Tube: what's it for?

This tube contains sodium fluoride and potassium oxalate, which preserve glucose for several days. It's mainly used for glucose testing but can mess up other enzyme tests.

Green Top Tube (GTT): what's it for?

This tube contains heparin, which stops clotting fast with no waiting. It's good for plasma chemistry and exotic animal blood work, but NOT for CBCs since it clumps white cells.

Blue Top Tube (BTT): what's it for?

This tube contains sodium or lithium citrate, which binds calcium to stop clotting. It's used only for coagulation tests and needs an exact 1:9 blood-to-additive ratio.

What is the order of draw for filling multiple tubes?

Fill in this order: blood cultures, blue (citrate), red (plain), SST (gel), green (heparin), lavender (EDTA), then gray (oxalate/fluoride) last. This order stops additives from crossing between tubes.

Why does the order of draw matter?

If tubes are filled out of order, leftover additive from one tube can carry into the next and mess up results. Tubes with clot-sensitive additives, like citrate, go early so they work correctly.

Why does icteric serum look yellow-orange?

It's from a buildup of bilirubin, a pigment made when red blood cells break down. High bilirubin usually points to a liver problem or excess red blood cell destruction.

Why does lipemic serum look cloudy or milky?

It's from extra fat (triglycerides) floating in the blood. This is common in non-fasted patients since fat from a recent meal hasn't cleared out yet.

Why does hemolyzed serum look pink or red?

Red blood cells ruptured and released hemoglobin into the liquid. This is often caused by rough handling, like forcing blood through a small needle or shaking instead of gently inverting the tube.

Why can hemolysis mess up test results?

Hemoglobin and other cell contents leak out and can falsely raise or lower values like potassium or certain enzymes. This is why gentle technique matters when transferring and mixing blood.

Why does dehydration affect lab results?

With less water in the blood, cells and proteins appear more concentrated than they really are. This can make readings like PCV or total protein look falsely high.

Why is it okay to let a patient drink water before a blood draw?

Water doesn't add fat or particles to blood, so it won't cause lipemia. Restricting water could actually cause dehydration, which throws off results a different way.

Why do we use EDTA (lavender top) instead of letting blood clot for a CBC?

A CBC needs whole blood with intact cells, not serum. EDTA stops clotting by binding calcium, so the cells stay whole and can be counted accurately.

Why can't the SST/tiger top gel tube be used for drug testing?

The silicone gel that separates clot from serum can absorb drug molecules out of the sample. This artificially lowers or hides the drug level, giving an inaccurate result.

Why does the green top (heparin) work faster than a red top or SST?

Heparin blocks the clotting cascade right away, so there's no need to wait 10 to 15 minutes for a clot to form. That makes it useful when you need results fast or only have a small blood volume.

Why is the blue top (citrate) 1:9 ratio so strict?

Too much or too little citrate changes how much calcium gets tied up, which throws off clotting time results. Coagulation tests are timing-based, so this ratio directly affects accuracy.

Why does the order of draw actually matter?

Tiny amounts of one tube's additive can end up contaminating the next tube during collection. Tubes most sensitive to contamination, like citrate for clotting tests, get filled first to avoid skewed results.

Why can't chemistry panels be run on lavender top (EDTA) samples?

EDTA binds calcium, and calcium is one of the values often measured on chemistry panels. It would give an artificially low or unreliable calcium and electrolyte reading.

Why can't the gray oxalate tube be used for chemistry panels or potassium testing?

Oxalate is a potassium salt, so it adds extra potassium into the sample and skews potassium readings. It also affects liver enzymes like alkaline phosphatase, making the panel unreliable.

What do icteric, lipemic, and hemolyzed serum look like compared to normal?

Normal serum is pale straw-yellow. Icteric serum is darker yellow-orange, lipemic serum is cloudy or milky, and hemolyzed serum is pink to red.

Why does the microhematocrit centrifuge need an extra inner lid secured?

The capillary tubes are thin and fragile, so if not locked down they can shift, dislodge, or shatter at high speed. The inner lid keeps them safely in place during the spin.

Is the swing-arm centrifuge restricted to certain tests or tubes?

Not really. It can handle both blood tubes and conical urine/fecal tubes, which a fixed-angle centrifuge can't do. Its real downsides are heat buildup damaging samples and layers re-mixing once it stops.

Why can't a fixed-angle centrifuge be used for urine or fecal sediment testing?

It can't hold conical-bottom tubes, which are shaped to concentrate sediment at the tip for urinalysis and fecal testing. Fixed-angle rotors only fit straight tubes held at a slant, not cone shapes.

What's the real test-availability difference between swing arm and fixed angle centrifuges?

Both can spin regular blood tubes for tests like chemistry and CBCs, there's no test only one machine can run. The real difference is conical tubes for urine sediment and fecal sedimentation: swing-arm can hold them, fixed-angle cannot.

Do SST (yellow/tiger top) tubes contain an anticoagulant?

No. Like the plain red top, blood is meant to clot in an SST tube, and the silica in the gel actually speeds up clotting rather than preventing it. The gel's only job is physically separating the clot from the serum after spinning.

Which tubes need blood to clot (serum) vs which need an anticoagulant (whole blood/plasma)?

Clot/serum tubes: plain red top and SST (yellow/tiger top). Anticoagulant tubes: lavender (EDTA), light gray (oxalate), green (heparin), blue (citrate), and dark gray (fluoride/oxalate).

Textbook order of draw vs. real clinic order: why might they differ?

The textbook order (cultures, blue, red, SST, green, lavender, gray) is built to avoid additive contamination between tubes. In real practice, some clinics fill the lavender (EDTA) tube first so the CBC sample can't clot before it's secured, lowering the risk of having to re-poke the patient.

Why might a clinic use red top instead of SST, or skip yellow top tubes?

Some clinics skip the SST gel tube and just use a plain red top for chemistry since it's simpler and cheaper if handled correctly. Yellow top tubes are more associated with human medicine and are used less often in general veterinary practice.