With the increasing recognition of overweight, obesity, and metabolic diseases in paediatrics, there is a need to apply more precise diagnostic methods to individualise the procedures and improve their monitoring. Advanced methods of evaluating body composition are a valuable addition to body weighing because they provide more precise data than screening methods such as anthropometry and bioelectrical impedance analysis (BIA). However, they require expensive equipment and highly trained staff. The availability of methods used in paediatrics is increasing. The article discusses the technical assumptions and summarises data from literature concerning the accuracy of chosen methods. From those, dual-energy X-ray absorptiometry (DXA) is distinguished as being widely accepted. Not only does it serve to evaluate bone density, but also to assess fat mass, making it a crucial element of multicomponent models (3C, 4C), which is often used separately as a reference method for other techniques. Methods based on body volume measurement are also of great importance. Traditionally they include hydrodensitometry (HW), which is being displaced by air displacement plethysmography (ADP), which is more acceptable among young patients. Numerous publications indicate that ADP may become a valuable alternative for widely used DXA. Isotope dilution methods are less popular in paediatrics, due to their cost and limited credibility, but are more commonly used among adults. The last group comprises imaging methods rarely used in the discussed indication. With the knowledge of available techniques and current clinical situation one can, for the patient's benefit, decide between screening and advanced techniques of body composition measurement.

Overweight, obesity, and metabolic syndrome in paediatrics represent issues of increasing importance. To complete diagnostics and extend patient monitoring, body composition measurements can be used. Nowadays there are a number of methods that allow the estimation of the content of individual tissues. Their accuracy and replicability, contributing to the measurement's credibility, are the subject of numerous scientific publications. While choosing a method, one has to know its basic assumptions and be aware of the assets and weaknesses, as well as its cost. The mentioned aspects will be discussed in this article. Reference methods considered as most precise are multicomponent models (3C, 4C), requiring several (usually three) measurements with the use of various devices, which improves the precision of calculating the fraction of a given body composition component (fat, water, minerals, and/or protein). Therefore, the need to estimate tissue content with mathematical models can be minimised. The choice of the methods forming a multicomponent model differs depending on the place of the examination. However, the 3C and 4C models are time-consuming and require sustained cooperation with young patients. Moreover, measurements can only be taken by trained staff that use expensive, specialised equipment. The examination cost can be reduced by the use of screening methods, such as anthropometrics and more advanced bioelectrical impedance analysis (BIA). Due to published comparisons with reference methods, the precision limits of screening methods are known. However, when executed correctly, measurements obtained with these methods have an acceptable replicability and can become a valuable tool in everyday practice.

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