Methods for Diagnosing Proteinuria—When to Use Which Test and Why: A Review

Proteinuria plays a central role in the diagnosis of kidney disease and has a high prognostic value. The test methods used differ considerably regarding their impact on test accuracy, sensitivity, and specificity. Therefore, knowledge of the methodology is crucial for the interpretation of the results. In addition to the distinction between semiquantitative and quantitative tests, there are also relevant differences within the 2 methods. In general, semiquantitative tests are easy to handle but have limitations such as incomplete quantification, a lack of specificity regarding the type of proteinuria, and a high rate of false-positive results that require retesting with a quantitative method for verification. In contrast, quantitative methods, especially immunoassays, have the advantages of high test accuracy and the possibility of targeted detection of specific protein molecules in addition to albumin. However, these methods are more expensive and require access to a laboratory or an electronic point-of-care device. In this Review, the different types of tests for proteinuria and their underlying methodologies and strengths and weaknesses are discussed in detail to allow a rational decision of use and the correct interpretation of the results depending on the clinical context.