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Serum proteins and urinary proteins electrophoresis are useful biological tests. They are often prescribed for the screening of monoclonal gammopathys and also during follow-up for treatment response. This test can be accredited according to standard NF ISO 15189 since laboratories use analysers and adapted reagents, but there are numerous protocols for the method validation. This paper present the results of a survey proposed in 2019 to biologists by CNBH and SFBC. The aim of this survey is to give biologists a choice among several protocols that have been positively evaluated by COFRAC.

The preanalytical phase is a key step in urinary protein measurement. It is a complex step, which includes urine sampling, storage and transport to the laboratory and preparation for analysis of the specimen. It can lead to numerous errors, since urine sampling is made by the patient himself. According to different cases, the procedures for urine sampling are presented in appendix 1 to 4. The aim of the presented guidelines is to improve the preanalytical step. In addition to the sampling made by a well-informed patient, the laboratory has to optimize transport and sample preservation, according to the analytes. The 24-hour urine collection is divided into aliquots with commercially available systems. Urinary proteins are measured on samples stored without preservatives. When 24-hour urine collection is not possible, a mid-stream urine sample is the most appropriate sample for protein measurement.

Urinary proteins or urinary albumin exhibit a high intra individual variability. Therefore, urine collected during 24 hours has been recognized as a reference biological fluid for usual values determination. However, urine collection during a day is difficult and numerous studies have been performed to replace the "gold standard" with measures on random samples and results given as protein/creatinine ratio or albumin/creatinine ratio, to decrease the variability. The paper presents the populations where ratios are well correlated with protein excretion, the cut-off values recommended in clinical settings and the limits of using ratio rather than 24 h excretion.

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Measurement of urine albumin has been introduced in the new classification of kidney disease (KD) as a marker for detecting, monitoring and predicting KD. Currently, the measure is not standardized. The variability of results obtained with commercially available procedures is important and can lead to misclassification of patients. Analytical standardization, started in 2007, is in progress. SRM 2925 primary reference material, SRM 3666 secondary reference material and liquid chromatography isotope dilution mass spectroscopy (LC-IDMS) reference measurement procedure are being validated by the National Institute of Standards and Technology (NIST). This report presents strategies and difficulties for developing this reference system.

Urinary protein electrophoresis analysis (UPE) is an essential investigation for the study of abnormal proteins in urines. The interpretation of this analysis must be comprehensive and relevant. Indeed, UPE is often requested by clinicians and may have an important impact in patient's management. This paper presents two cases with free light chains showing unexpected electrophoretic migration which can lead to the misinterpretation of results. This article helps biologists to keep in mind the interest of UPE among the several analyses useful in the laboratory.