Diagnostic lab equipment

Question 1

Name different types of diagnostic lab equipment

Answer 1

Compound light microscope.

Centrifuge / stat spin.

Micro-haematocrit centrifuge.

Biochemistry analyser (Idexx Vet test / Calalyst one).

Haematology analyser (Idexx ProCyte / LaserCyte).

Blood gas and/ or electrolyte machine (Vetstat).

SnapPro analyser.

Question 2

Describe a compound light microscope

Answer 2

This is an essential piece of lab equipment that is commonly used for disease diagnosis.

The microscope uses lenses and light to magnify the image to allow visualisation and identification.

Can have one (Monocular) or two (binocular) eye pieces.

Commonly there are 3-4 objective lenses allowing varying degrees of image magnification.

Question 3

Describe objective lenses

Answer 3

X 4 A main scanning lens ( not all microscopes are fitted with this lens). Allows detailed visualisation of macroscopic objects and overall scanning of the slide.

X 10 Low power objective. Used for locating area of interest.

X 40 High power -A dry lens used for more detailed focusing

Question 4

Describe oil immersion lens (x100)

Answer 4

X 100 Oil Immersion -A powerful lens which uses light refracted through an oil layer rather than through air.

Only lens that should be used for oil immersion.

This lens is commonly longer in length than other lenses, care should be taken when moving it into place, to avoid damage to the slide or lens.

Question 5

Describe the battlement technique

Answer 5

The slide is examined systematically to ensure all of the slide is covered and to prevent double counting of cells.

Two fields up, two fields along and two fields down

Question 6

Describe the vernier scale

Answer 6

Positioned on the horizontal and vertical axis of the stage.

Allows relocation of a particular point on a microscope slide.

Main scale divided into millimetres.

Vernier plate divided into 10 divisions

When record your reading it is important to note the position of label on slide (right or left)

It is important to record the co-ordinates of the object using BOTH X axis (left to right) and Y axis (top to bottom) readings

If slide has been sent to referral lab, co-ordinates for upper right corner or lower left corner of coverslip should also be noted.

Question 7

What is a centrifuge?

Answer 7

The centrifuge spins a substance at high speed using centrifugal force to separate the fluid portion (supernatant) from the solid portion (sediment).

An electric motor rotates at high speed around a fixed axis applying perpendicular force to the axis

Question 8

What are the two types of centrifuge?

Answer 8

Swinging arm

angled head

Question 9

Describe a swinging arm centrifuge

Answer 9

This has moveable specimen cups that are suspended vertically from arms. As the rotor speed increases the cups swing out into horizontal position.

This results in supernatant that is uniformly distributed therefore easy to remove with pipette.

Limitations include heat build up at high speeds than can damage sample

Some, larger centrifuges have in built temperature control (4°C optimum for fluid separation)

Question 10

Describe an angled head centrifuge

Answer 10

Tubes are positioned at 25-40 degree angle within centrifuge.

Supernatant collects at an angle so more difficult to collect

Higher speeds can be achieved.

Question 11

Describe the incubator

Answer 11

Predominantly used for incubation of samples for bacterial culture

Double walled metal container with insulation material e.g. fibreglass between the two

Double insulated doors; inner glass and outer metal allow contents of incubator to be viewed without heat loss from cabinet.

Electrical heating element inside cabinet

Temps range from 25-100°C, usually maintained at 37 ̊̊C

Wire shelves allow air circulation

Thermostat is used in conjunction with an internal thermometer to ensure the appropriate temperature is maintained.

Plates placed lid side down on wire shelves to reduce condensation on agar surface.

Incubators require annual servicing and cleaning should take place daily.

Question 12

Why might a bunsen burner be used?

Answer 12

During preparation of agar plate for bacterial culture (loop sterilisation)

Fixing bacteria on microscope slide prior to staining

Heating liquid in a glass beaker

Question 13

Define refraction

Answer 13

The change of velocity and resulting bending of light as it passes from one medium to another with different optical density e.g. air into urine

Question 14

What is a refractometer?

Answer 14

Cylindrical instrument with prism and calibration scale

Measures Specific gravity of urine and other fluids

Measures protein concentration of plasma and other fluids (grams/deciliter g/dl)

Question 15

Describe the use of a refractometer

Answer 15

MUST be calibrated before EVERY use, using distilled water.

The reading is taken on the graduated Sg scale at the blue/white line interface

Units are temperature compensated (between 60-100°C), therefore, temperature fluctuations are unlike to affect results.

Precise, accurate, durable, easy to use, cheap to buy and only small volume of sample required to achieve result.

Question 16

What are the advantages of a glucometer?

Answer 16

Fast, reliable and accurate method of blood glucose level examination.

Small drop of sample required.

Minimal trauma for patient.

Allows regular and accurate blood glucose measurements to be obtained.

Question 17

Describe commercial test kits

Answer 17

In house serology test kits

Reliable, easy to use and immediate results

Test for infectious disease antigens and antibodies, hormones and immunoglobulin levels

Predominantly ELISA test which are mircowell or membrane based

Immunomigration and agglutination tests also available

Question 18

Describe ELISA test kits

Answer 18

The majority of commercial test kits use Enzyme linked Immunosorbent Assay ELISA technology

ELISA test wells are impregnated with appropriate antibodies for a specific antigen, depending on the disease, virus, hormone etc. being tested for.

Antibodies within the test well bind to the viral antigen present in the sample.

A dye is activated resulting in a colour change within the test well. This will indicate a positive result

Question 19

What are the advantages of using an ELISA test?

Answer 19

Detect the presence of viral antibody or antigen.

High specificity and sensitivity associated with these tests reducing risk of inaccurate results

Eliminates requirement for expensive and time consuming viral isolation and identification providing immediate results.

Question 20

What is the different between a direct and indirect ELISA test?

Answer 20

The direct ELISA employs antibodies to detect the presence of a particular antigen in a sample (FeLV)

The indirect ELISA is used to determine the presence of a particular antibody in a specimen such as serum (FIV) antigen v low in positive cats

Question 21

Why might animals get a false positive from an ELISA test?

Answer 21

False positives can occur in animals that have be recently vaccinated with a live virus. The animal with carry viral antibodies but may not be not be a carrier of the actual virus

FIV

Kittens can have positive antibodies passed on from their infected mother , however, they may not have the disease

Question 22

What should positive FELV tests be supported by?

Answer 22

immunofluorescent antibody assay

Question 23

Describe a urine dipstick

Answer 23

Urinalysis reagents strips e.g. Dipstix, Multistix, BM-Test-8.

Used to test urine biochemistry e.g. protein, glucose, ketones, blood, pH, Nitrites, Specific gravity, urobilinogen and bilirubin.

Inaccurate results can commonly occur if test strips have passed expiry date or patient has received drug therapy.

Designed to measure human urine parameters (S.g. normally inaccurate)

Question 24

What must be done to prevent errors from urine dipsticks?

Answer 24

A fresh sample must be used to avoid inaccurate results due to sample contamination and break down of chemistry’s present within the sample.

Exposure to sunlight will oxidize bilirubin and urobilinogen leading to falsely low readings

Erroneous readings for blood and glucose can occur if disinfectants present in sample container

Test strips for individual chemicals are available