Methods for Diagnosing Proteinuria: When to Use Which Test, and Why.

Abstract

Proteinuria plays a central role in the diagnosis of kidney disease and has a high prognostic value. The test methods used differ considerably regarding 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 semi-quantitative and quantitative tests, there are also relevant differences within the two methods. In general, semi-quantitative tests are easy to handle but have limitations such as: i) incomplete quantification, ii) a lack of specificity regarding the type of proteinuria, iii) a high rate of false positive tests with the need for re-testing with a quantitative method for verification. In contrast, quantitative methods, especially immunoassays, have the advantages of: i) high test accuracy, ii) 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, their underlying methodologies and their strengths and weaknesses are discussed in detail to allow a rational decision of use and a correct interpretation of the results depending on the clinical context.