Blood Tests: Methods, Analysis, and Safety
Tests on Blood Cells
Blood tests commonly analyze:
- Red blood cells (RBC): 4.5-5.5 million
- White blood cells (WBC): 6,000-10,000
- Blood platelets: 200,000-800,000
Centrifugal Method
By spinning blood in a centrifuge, blood cells sediment at the bottom of the test tube. Most of this column consists of red blood cells, with other cells forming a thin, buffy layer on top. The volume of packed red cells is expressed as a percentage of the total blood volume.
Conductivity (Coulter) Method
This method uses the fact that blood cells have a much lower electrical conductivity than the solution in which they are suspended. It consists of a beaker with diluted blood. Negative pressure generated by a pump causes a flow of solution from the beaker through an orifice into a glass tube. Each time a blood cell is swept through the orifice, it temporarily blocks part of the electrical current path.
Microscope Method
Diluted blood flows through a thin cuvette (4). The cuvette is illuminated by a cone-shaped light beam obtained from a lamp (1) through a ring aperture (3) and an optical system (2). The cuvette is imaged on the cathode of a phototube (7) by means of a lens (5) and an aperture (6). Normally, no light reaches the phototube until a blood cell passes through the cuvette and reflects a flash of light on the phototube.
Chemical Tests on Blood
Common methods include:
- Colorimeter or Filter-photometer method
- Chloridemeter
- Spectrophotometer
- Autoanalyzer
Colorimeter or Filter-photometer Method
This method measures the transmittance and absorbance of solutions. A filter (F) selects a suitable wavelength range from a lamp’s light. This light falls on two photoelectric (selenium) cells: a reference cell (CR) and a sample cell (CS).
Flame Photometer
For measuring sodium and potassium, a different property is utilized: the color of the flame. A flame appears yellow (sodium) or violet (potassium) when their solutions are aspirated into the flame.
Chloridemeter
For determining chlorides, a special instrument (chloridemeter) is sometimes used, based on an electrochemical method. The chloride is converted into silver chloride using a silver wire electrode.
Spectrophotometer
In this device, the filter of the colorimeter is replaced by a monochromator. A monochromator uses a diffraction grating (G) (or a prism) to disperse light from a lamp that falls through an entrance slit (S1) into its spectral components.
Autoanalyzer
Mixing, reaction, and colorimetric determination take place sequentially in a continuous stream, not in individual test tubes for each sample. The sampler feeds samples into the analyzer in time sequence. A proportioning pump meters the sample and reagent. Mixing is achieved by injecting air bubbles. The mixture is incubated while flowing through heated coils.
Physiological Effects of Electrical Current
Electrical accidents are caused by the interaction of electric current with body tissues. For an accident to occur, current of sufficient magnitude must flow through the victim’s body, impairing vital organs. The physiological effects depend on:
- Magnitude of current
- Current pathway through the body
- Location of application of shock
The heart’s current sensitivity is much higher. The effect of current applied directly to the heart is often referred to as microshock, while the effect of current applied through the surface is called macroshock.
Electric current can affect tissue in two ways:
First effect: Electrical energy dissipated in tissue resistance can cause a temperature increase. If a high enough temperature is reached, tissue damage (burns) can occur.
Second effect: An external electric current of sufficient magnitude can cause local voltages that trigger action potentials and stimulate nerves. When sensory nerves are stimulated, the electric current causes a “tingling” or “prickling” sensation, which at sufficient intensity becomes unpleasant and even painful.
Methods of Electric Shock Accident Prevention
- Grounding
- Double Insulation
- Protection by Low Voltage
- Ground-Fault Circuit Interrupter
- Isolated Power Distribution Systems
Telemedicine
Telemedicine is the application of telecommunications and computer technology to deliver health care from one location to another. It involves using modern information technology to deliver timely health services by electronically transmitting the necessary information.
Telemedicine Applications
The main applications of telemedicine are in radiology, pathology, cardiology, and medical education.
Essential Parameters for Telemedicine
- Primary Patient Data
- Patient History
- Clinical Information
- Investigations, Data, and Reports