This content is suitable for medical technologists/technicians/lab assistants/scientists writing the SMLTSA board exam. The content is also suitable for biomedical technology students and people also interested in learning about test methodologies used in medical technology. This chapter describes test methodologies and their uses. Please note that these notes are a collection I used to study for my board exam and train others who got distinctions using these. Disclaimer: Credit goes to those who wrote the notes and the examiners of each exam question. Please use only as a reference guide and use your prescribed textbook for the latest and most accurate notes and ranges. The material here is not referenced as it is a collection of pieces of study notes from multiple people, and thus will not be held viable for any misinterpretations. Please use at your own discretion.

1. Test Methodologies
Chemical Pathology

2. Objectives
• Demonstrate knowledge of the principles of
the test methodologies in the range.
• Range: Potentiometry; colorimetry;
enzymatic/ kinetic; turbidimetry;
nephelometry; enzyme immunoassay;
chemiluminescence.
• Demonstrate knowledge of the individual
principles of the manual and automated
testing procedures used in the estimation of
all the analytes in the range.
• Demonstrate knowledge of the limitation of
the test methods, interfering substances and
detection limits.

3. Objectives
• Process samples in accordance with documented
laboratory procedures.
• Utilize the correct units for reporting the results
of the analytes.
• Describe appropriate physiological conditions
affecting test results.
• Follow the correct procedures when handling
critical/life threatening results.
• Demonstrate knowledge of the application of the
normal reference ranges of all the tests in the
range and ability to correlate laboratory results
with physiological and pathological conditions.

4. Test Methologies
• Potentiometry;
• Colorimetry;
• Enzymatic/ kinetic;
• Turbidimetry;
• Nephelometry;
• Enzyme immunoassay;
• Chemiluminescence
• Electrophoresis

5. Ion Selective Electrodes (ISE)
• Potentiometric methods of analysis involve
the direct method of electrical potential due
to the activity of free ions.
• ISEs are designed to be sensitive toward
individual ions.
• Basic components: Indicator electrode,
reference electrode, voltmeter, salt bridge, H+
sensitive glass tip, buffered acid solution, salt.

6. pH Electrode

7. Principle of ISE Measurements
• Two electrodes are in contact with the same
buffer solution.
• The one electrode (ISE), indicator or measuring
electrode is only sensitive for a specific ion. (Na,
K, Cl, Ca, H). This ISE is in contact with the sample
(serum, calibrator) plus the buffer solution.
• The other electrode, reference electrode is in
contact with the buffer solution only.
• Both electrodes are connected to a
potentiometer. (voltmeter, computer)
• If none of the specific ion is present in the
sample, there is a zero (constant) potential
between the electrodes.

8. Principle of ISE Measurements
• If the specific ion is present in the sample, the
ISE will change the potential between the two
electrodes. The potential difference is equal to
the ion concentration.
• The ion concentration is calculated using the
Nernst equation.
• The instrument is calibrated (standardised)
using known calibration solutions (standards).

9. ISE Measurement Electrodes
• Sodium (Na): Glass electrode
• Potassium (K): Valinomycin membrane
• Chloride (Cl): Ag/AgCl
• Carbon Dioxide (CO2): pH electrode with
silicone rubber membrane
• Calcium (Ca): Ionophore

10. Two Types of ISE Measurements
• Direct ISE Measurements:
• The ISE is directly in contact with the sample
(serum, calibrator). No pre-dilution of sample.
• Indirect ISE Measuments:
• Sample (serum, calibrator) is pre-diluted with
a high ionic strength buffer before
introduction onto the tip of the ISE. Sample is
pre-diluted.
• Pseudohyponatraemia: disadvantage

11. Pseudohyponatraemia
• This is a disadvantage with indirect ISE
measurement is due to a high (increased) lipid
and/or protein content in the sample.
• It will result in “false” low electrolyte results,
more notable in sodium concentration.
• (Sample volume error in the electrolyte
containing compartment).
• This effect is not so severe if only the protein
concentration is increased.

12. Correcting Sodium
• Correcting Sodium for high Protein
Corrected Na= Na + [(TP-80)x0.25]
• Correcting Sodium for high Triglycerides
Corrected Na= (Trig x 0.18) + Na

13. Summary
• Summarise the principle in a fully labelled
diagram.
• Name the different types of electrode
membranes.
• Name two (2) differences between the direct
and indirect ISE.
• Define pseudohyponatraemia.

14. Basic components of Photometry
• Light source
• Wavelength selector
• Collimating lens
• Slit
• Filter
• Prism
• Diffraction grating
• Slit
• Cuvette holder
• Photosensitive cell
• Galvanometer

15. Spectrophotometer

16. Photometry
Photometry depends on:
• Colour in a substance
• Intensity of that colour
Colour Wavelength
• Red 630
• Orange 590
• Yellow 560
• Green 510 Visible
• Blue 480 Increasing energy
• Indigo 450
• Violet 420
• Ultraviolet 340
• Proteins 280 UV
• DNA 260

17. Simple Spectrophotometer
(Colorimeter)

18. TYPES OF SPECTROPHOTOMETERS
• Double-beam
• Splits light beam —
–one portion to reference cuvette
–one portion to the sample cuvette
• Flame photometer
• Measures ions (Na and K) in body fluids
• Back-up instrument
• Metal ions sprayed into flame – emit light of
characteristic colour

19. TYPES OF SPECTROPHOTOMETERS
• Atomic absorption
• Measures absorption of light of a unique
wavelength by atoms in the ground state
• Uses heat from a flame to produce free atoms
• Used to detect extremely low concentrations
• Fluorometry
• Measures the lower energy of a molecule
exposed to a certain wavelength light

20. Interferences
• Alignment – from light source to detector
• Dirt particles – interference when in path of
light source
• Stray light – around slits, cuvette holder
• Unstable current – fluctuating light source

21. SPECTROPHOTOMETRY
• Determines concentration of coloured solutions.
• Frequently used instrument in the lab
• 1) independently used
• 2) part of an analyzer
• Measurement is done by passing beam of light
through a solution. The portion that passes
through is % Transmission. Light not passed
through by the solution is measured as Absorbed.

22. Parts of a Spectrophotometer
• Light source – provides light beam e.g. Tungsten
UV
• Monochromator – has diffraction grating –
disperses light into spectrum. It isolates beam to
one wavelength (one colour of light).
• Cuvette – holds solutions
• Photo detector/photoelectric cell – converts
light/energy to electrical current
• Galvanometer/amperometer/recorder/digital
display – current magnitude generated by a
detector can be measured by these devices.

23. BEER-LAMBERT LAW
• Light passing through a coloured medium is
absorbed in direct proportion to the amount of
the coloured substance in the light path.
• A = abc
• A – absorbance (light absorbed, also OD)
• Constants: a – absorptivity (extinction coefficient)
• b – length of light path through solution
• c – concentration of the coloured compound
• A=c, for calculations use: Au/As=Cu/Cs

24. Turbidity and Nephelometry
Light scattering
• Light scattering is the physical phenomenon
resulting from the interaction of light with a
particle(s) in solution.
• Dependent on:
• Particle size
• Wavelength
• Distance of observation,
• Concentration of particles
• MW of particles

25. Principles
• Chemical analysis based on the phenomenon
whereby light, passing through a medium with
dispersed particles is attenuated in intensity by
scattering.
• In turbidimetry, measures the decrease in
intensity of the incident light-beam that is caused
by scattering, reflectance and absorption of the
light.
• In nephelometry, the intensity of the scattered
light is measured, usually, but not necessarily, at
right angles to the incident light beam. 300
(forward scatter) and 900 angles.
• More sensitive and has lower limit of detection.

26. Interferences
• Turbidity can be measured on most routine
analysers by a spectrophotometer (absorbed
light)
• Reduced sensitivity and precision.
• Extent of light scattering increases as
wavelength increases
• The intensity of scattered light is normally
measured by nephelometer.

27. APPLICATIONS
• Immunoglobulins,
• Specific proteins: Haptoglobin, Transferrin,
Alpha 1 AT, Lipoproteins, Albumin
• Coagulation factors: Antithrombin III
• Theraputic drugs

28. Summary
• Name the similarities and differences between
turbidimetry and nephelometry.

29. Chromatography
• Involves a sample (or sample extract) being dissolved in
a mobile phase (which may be a gas, a liquid or a
supercritical fluid).
• The mobile phase is then forced through an immobile,
immiscible stationary phase.
• The phases are chosen such that components of the
sample have differing solubilities in each phase.
• A component which is quite soluble in the stationary
phase will take longer to travel through it than a
component which is not very soluble in the stationary
phase but very soluble in the mobile phase.
• As a result of these differences in mobilities, sample
components will become separated from each other as
they travel through the stationary phase.

30. HPLC and GC
• Techniques such as H.P.L.C. (High Performance
Liquid Chromatography) and G.C. (Gas
Chromatography) use columns - narrow tubes
packed with stationary phase, through which the
mobile phase is forced.
• The sample is transported through the column by
continuous addition of mobile phase.
• This process is called elution.
• The average rate at which an analyte moves
through the column is determined by the time it
spends in the mobile phase.

31. Chromatography

32. Bi-directional increases sensitivity

33. Enzymes
• Enzymes are proteins that catalyze (i.e., increase
the rates of) chemical reactions.
• In enzymatic reactions, the molecules at the
beginning of the process, called substrates, are
converted into different molecules, called
products.
• Almost all chemical reactions in a biological cell
need enzymes in order to occur at rates sufficient
for life.
• Since enzymes are selective for their substrates
and speed up only a few reactions from among
many possibilities, the set of enzymes made in a
cell determines which metabolic pathways occur
in that cell.

34. Catalysts
• Most enzyme reaction rates are millions of
times faster than those of comparable un-
catalyzed reactions.
• As with all catalysts, enzymes are not
consumed by the reactions they catalyze, nor
do they alter the equilibrium of these
reactions.
• However, enzymes do differ from most other
catalysts in that they are highly specific for
their substrates.

35. Enzyme activity
• Enzyme activity can be affected by other
molecules.
• Inhibitors are molecules that decrease enzyme
activity; activators are molecules that increase
activity. Many drugs and poisons are enzyme
inhibitors.
• Activity is also affected by temperature,
chemical environment (e.g., pH), and the
concentration of substrate and enzymes.

36. Michaelis-Menten constant (Km)
• Is the substrate concentration required for an
enzyme to reach one-half its maximum
reaction rate.
• Each enzyme has a characteristic Km for a
given substrate, and this can show how tight
the binding of the substrate is to the enzyme
• Law of mass action.

37. Inhibitors
• In competitive inhibition, the inhibitor and
substrate compete for the enzyme (i.e., they
can not bind at the same time). Often
competitive inhibitors strongly resemble the
real substrate of the enzyme.
• The maximal rate of the reaction is not
changed, but higher substrate concentrations
are required to reach a given maximum rate,
increasing the apparent Km.

38. Inhibitors
• In uncompetitive inhibition, the inhibitor
cannot bind to the free enzyme, only to the
ES-complex. The EIS-complex thus formed is
enzymatically inactive. This type of inhibition
is rare, but may occur in multimeric enzymes.

39. Inhibitors
• Non-competitive inhibitors can bind to the enzyme at
the binding site at the same time as the substrate, but
not to the active site.
• Both the EI and EIS complexes are enzymatically
inactive.
• Because the inhibitor can not be driven from the
enzyme by higher substrate concentration (in contrast
to competitive inhibition), the apparent Vmax changes.
• But because the substrate can still bind to the enzyme,
the Km stays the same.
• Mixed inhibition
• This type of inhibition resembles the non-competitive,
except that the EIS-complex has residual enzymatic
activity.This type of inhibitor does not follow Michaelis-
Menten equation.

40. Enzyme naming
• An enzyme's name is often derived from its
substrate or the chemical reaction it catalyzes,
with the word ending in -ase.
• Examples are lactase, alcohol dehydrogenase and
DNA polymerase.
• This may result in different enzymes, called
isozymes, with the same function having the
same basic name.
• Isoenzymes have a different amino acid sequence
and might be distinguished by their optimal pH,
kinetic properties or immunologically.
• Isoenzyme and isozyme are homologous
proteins.

41. Enzyme kinetics
• Fixed time point- not reliable
• Continuous- most reliable,
• measured every second i.e. Progress noted
from star to end of reaction, interfering
substances like inhibitors can be picked up.

42. Summary
• List ten (10) enzymes tested in a Chemistry
lab.
• List (6) factors that influence the rate of
reaction of enzymes.
• Briefly explain the 3 types of inhition
mechanisms.

43. Enzyme-linked immunosorbent assay
(ELISA)
• A popular format of a "wet-lab" type analytic
biochemistry assay that uses one sub-type of
heterogeneous, solid-phase enzyme immunoassay
(EIA) to detect the presence of a substance in a
liquid sample or wet sample.
• Heterogenous assays are those assays that need to
separate some component of the analytic reaction
mixture, e.g. by adsorbing some components on to a
solid phase which is either physically immobilized
e.g. in ELISA, or spatially separable e.g. by magnetic
or centrifugal or other forms of physical separation,
and unwanted components are thrown away
(washed or aspirated or centrifuged etc).

44. Enzyme-linked immunosorbent
assay (ELISA)
• Traditional ELISA typically involves
chromogenic reporters and substrates that
produce some kind of observable color change
to indicate the presence of antigen or analyte.
• Newer ELISA-like techniques utilize
fluorogenic, electrochemiluminescent, and
real-time PCR reporters to create quantifiable
signals

45. Enzyme-linked immunosorbent
assay (ELISA)

46. The steps of "indirect" ELISA
• A buffered solution of the antigen to be tested
for is added to each well of a microtiter plate,
where it is given time to adhere to the plastic
through charge interactions.
• A solution of non-reacting protein, such as
bovine serum albumin or casein, is added to
block any plastic surface in the well that
remains uncoated by the antigen.

47. The steps of "indirect" ELISA
• Next the primary antibody is added, which
binds specifically to the test antigen that is
coating the well. This primary antibody could
also be in the serum of a donor to be tested
for reactivity towards the antigen.
• Afterwards, a secondary antibody is added,
which will bind the primary antibody. This
secondary antibody often has an enzyme
attached to it, which has a negligible effect on
the binding properties of the antibody.

48. The steps of "indirect" ELISA
• A substrate for this enzyme is then added. Often,
this substrate changes colour upon reaction with
the enzyme. The colour change shows that
secondary antibody has bound to primary
antibody, which strongly implies that the donor
has had an immune reaction to the test antigen.
This can be helpful in a clinical setting, and in
R&D.
• The higher the concentration of the primary
antibody that was present in the serum, the
stronger the colour change. Often a spectrometer
is used to give quantitative values for colour
strength.

49. Microplates

50. Summary
• Summarise the steps involved in indirect ELISA
using a diagram.

51. Chemiluminescence
• Chemiluminescence is the term for process of
exciting molecules by chemical means and
measuring the light emitted as the molecules
return to their stable, unexcited state.
• When chemiluminescent reactions are catalyzed
by enzymes, the reaction is termed
bioluminescent.
• Light can be emitted either directly from the
reacting molecule or indirectly as energy is
transferred to a molecule capable of light
emission.

52. Chemiluminescence
• Because the excitation is carried out by
chemicals means, the instruments consist only
of a photodetector (a luminometer) to
measure the intensity of light emitted from
the reaction tube.

53. Chemiluminescence Principle
• Chemiluminescence is a reaction that emits
energy in the form of light.
• The analyte is bound by a specific antibody
attached to a carrier, e.g. Bead or magnetic
particle.
• The solution is washed to remove unbound
material.
• The chemiluminescent labelled antibody
which binds to the antigen-antibody complex.

54. Chemiluminescence Principle
• Light is produced by the hydrolysis of the
label or by adjusting the pH of the
mixture.
• The amount of light produced is
measured in a photometer and the
concentration of the analyte is calculated
from a calibration curve.

55. Summary
• Summarise the Chemiluminescence principle
using a diagram.

56. Electrophoresis
• The process of separating the charged
constituents (proteins) of a sample (serum) by
utilizing an electrical current, a suitable buffer
and a support medium.
• At pH 8.6 all serum proteins are negatively
charged (anions) and will therefore move to
the positive electrode (anode).

57. Principle and Components
• Electrophoresis is the process of separating
the charged constituents of a sample by
means of an electrical current.
• Charged particles placed in an electrical field
migrate towards either the anode or cathode.
• Depending on their net charge.
• The rate of migration varies with the net
charge, the strength of the electrical field.
and the weight or size of each particle.

58. Principle and Components
• In electrophoretic analysis the apparatus is
designed so that an electrical current passes
between the two electrodes and through the
sample and its support medium.
• An electrophoresis chamber consists of two
buffer compartments separated by a dividing
wall: one side contains the anode and the
other the cathode (platinum wire or carbon
electrodes).
• Each compartment is filled with the same
height with a buffer.

59. Electrophoresis
• An electrical “bridge” across the top of the
dividing wall is created by the support
material for the separation.
• The support wall material may be composed
of an agarose gel, an acrylamide gel, or a
moist cellulose acetate membrane that is in
contact with the buffer in each compartment.
• The only electrical connection between the
two compartments is by way of the support
material bridge.

60. Electrophoresis
• The sample is gently applied to the surface of
the bridge, and a voltage is applied to the
electrodes.
• The current is carried across the bridge by
both the buffer ions and the migrating
charged particles in the sample.
• When a buffer of pH 8.6 is used to
electrophoretiically separate a serum sample,
all the serum proteins carry a net negative
charge and migrate toward the anode.

61. Electrophoresis
• Albumin is relatively small and carries the
largest charge; it therefore moves the fastest.
• The gamma globulins are large proteins and
have the small net charge;
• they move the least distance.
Cathode(-) Anode (+)

62. Summary
• State the principle of electrophoresis including
a drawing of the different fractions fro the
cathode to the anode.
• Arrange this family (represents the different
fractions) according to size from the anode to
the cathode.
• Mommy Beta, Daddy gamma, Sister alpha-1,
Brother alpha-2, Baby Albumin

63. Word Association
Arrange the Simpsons
family (represents the
different fractions)
according to size from
the anode to the
cathode.
Mommy Beta; Daddy
gamma; Sister alpha-1;
Brother alpha-2; Baby
Albumin

64. More detailed Electrophoresis notes, on the
separate Electrophoresis powerpoint.