Osmometry is a medical and pharmaceutical procedure that determines the osmotic value or pressure of a substance. It is considered, for example, to measure plasma osmolality. To be able to perform it, an osmometer is needed.
What is an osmometer?
Osmometry is used, for example, to determine plasma osmolality, which is a property of blood plasma. Osmometry looks back on a long history that is not only related to medicine – because the method is also used in a variety of other applications. In 1828, the botanist Henri Dutrochet is said to have documented the first osmometer. Today, static and dynamic, direct and indirect measurement techniques provide a range of different methods. An osmometer measures the osmotic value or osmotic pressure of a substance. In biology, osmosis is the diffusion of water or other liquids through a semipermeable membrane. In the human body, osmotic processes play an important role in numerous micro- and macro-level processes. A disturbance of the osmotic balance can, for example, lead to water retention in tissues (edema) or affect the exchange of molecules between cells and their environment. Osmometry is a measurement method that is also used in medicine. It is used, for example, to determine plasma osmolality, which is a property of blood plasma and refers to the number of particles that have an osmotic effect. Osmometry does not measure osmolality as an absolute value, but makes a comparison between the sample present for testing and a reference substance such as pure water (H2O). Both substances should be at the same temperature, otherwise the measurement results may develop inaccuracies and may not be usable. Once this possible source of error is eliminated, the only remaining significant factor affecting osmolality is the concentration of osmotically active substances in the sample.
Forms, types, and species
Osmometry can employ a variety of methods to obtain the measurement results sought. To determine osmolality, osmometers draw on a reference value to which they compare a particular measurement result of a sample. Different substances can serve as a reference; however, osmometers frequently resort to pure water that has no additional substances dissolved in it. This means that it has a freezing point of 0° C and allows conclusions to be drawn about the reference sample. In many cases, medicine and pharmacy use osmometers that determine osmolality using the method of freezing point osmometry. This is a special method that compares the freezing point of the sample with that of water. The freezing point of solutions changes depending on the substances dissolved in them. Saltwater solutions or blood samples, which have a high salt content, only freeze at a significantly lower temperature than pure water.
Structure and mode of operation
From the outside, typical osmometers represent plain boxes that have a measuring point for inserting a sample. In the medical field, such a sample is usually a blood sample, for example, to calculate the osmolality of blood plasma. The measurement takes only a short time and thus allows an economically reasonable procedure. Depending on the technical design of the osmometer, substances of different aggregate states (solid, liquid or gaseous) can be tested. Some osmometers can be connected to a computer via a USB plug or other connection, thus allowing rapid evaluation of the data and almost immediate viewing of the measurement results. Serial measurements and measurements with small amounts of test material (for example, blood samples) are also possible with many instruments.
Medical and health benefits
Osmometry can be useful in practically applied medicine as well as in medical research, providing important insights into osmotic processes in the human body. For example, it can be used to diagnose plasma osmolality. Plasma osmolality is a characteristic of blood plasma.The property describes how many particles within the blood plasma have an osmotic effect. Physicians can calculate plasma osmolality using a formula that can usually be used to make a rough estimate. To do this, the factor 1.86 is multiplied by the measured sodium value, whereupon the equation adds urea and glucose values. Finally, the summand 9 is added. The formula provides an approximate trend of osmolality. However, direct measurement of this property of blood may provide more accurate results in some circumstances. For example, the formula does not take into account possible osmotic substances that may be present in the blood. This and other influencing factors result in a so-called osmotic gap, which describes the difference between calculated (i.e., rather estimated) and actually measured value for osmolality. In healthy people, this osmotic gap is less than the amount of 10. An osmolality of 275-320 mosmol per kg body weight is considered normal. If the measured value is significantly above this normal value, it may indicate a disease. Certain diseases are accompanied by a characteristic pattern of symptoms, which doctors can use to identify them. Correct diagnosis is a prerequisite for the most successful treatment possible.
