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Point-of-care testing
Introduction
Point-of-care (POC) testing is an ever-expanding area of biomedical science and is now essential to efficient patient care. As the name implies, the goal is to collect the specimen to be tested and obtain the results in a short period of time ( Fig. 14.1 ). This ideally should be done at, or at least near, the location of the patient. All processes are integrated and automated.
Historically, blood gas analysis was the forerunner of POC testing, with blood glucose analysis revolutionized diabetic care.
Now tests as diverse as human immunodeficiency virus, C-reactive protein, haemoglobin A1C and cardiac markers can be rapidly obtained at the POC. Use of polymerase chain reaction technology has allowed the detection and measurement of the specific genetic material of bacteria, viruses, etc.
This chapter considers only a few of the available POC tests and goes into detail on some of the more common machines seen in healthcare theatres.
HemoCue, haemoglobin measurement ( Fig. 14.2 )
A reliable compact device that measures haemoglobin concentration.
Components
- 1.
A handheld and portable device houses a photometer.
- 2.
It has a disposable microcuvette into which a drop of capillary, venous or arterial blood is placed.
Mechanism of action
- 1.
The microcuvette contains a dried reagent mixture. Sodium deoxycholate haemolyses red blood cells, releasing the haemoglobin. Sodium nitrite converts haemoglobin to methaemoglobin, which, together with sodium azide, gives azide methaemoglobin.
- 2.
A specific photometer is housed in the device and measures the absorbance at 570 nm and 880 nm.
- 3.
Results are displayed digitally almost immediately.
Problems in practice and safety features
- 1.
Quality control is necessary to ensure accuracy is maintained.
- 2.
The microcuvettes need to be stored in a dry environment.
Hemochron Junior, activated clotting time measurement
This is a compact, mains or battery-powered device that measures activated clotting time (ACT) ( Fig. 14.3 ). The ACT is used to monitor unfractionated heparin therapy.
Each different version of an ACT machine has its own baseline reference value. The normal range for the Hemochron Junior is usually between 90 and 140 seconds.
After a dose of unfractionated heparin, the measured ACT value should rise. The two versions of cuvette commonly used are low range and high range.
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