Determining the protein / creatinine ratio is a modern alternative to determining the concentration of protein in daily urine.

      Until recently, determination of protein concentration in daily urine was considered the “gold standard” in the diagnosis of proteinuria. And this had a very good reason. The fact is that the qualitative and quantitative composition of urine changes significantly during the day, and the determination of protein in daily urine makes it possible to neutralize the effect of diuresis on protein concentration in urine. We give an example: in a patient with a protein excretion of 0.5 g per day, the protein concentration in the urine can vary from 1 g / l (with daily diuresis of 0.5 l) to 0.2 g / l (with daily diuresis of 2, 5 l).

      However, collecting daily urine is a very complicated process even for hospital patients, and it is practically impossible for young children and elderly patients. And what about emergency hospitals, in which urgent patients are received around the clock, and the first urinalysis can be performed only from a single portion received at the time of hospitalization?

   Long-term scientific studies on the search for an alternative to daily urine analysis have shown that the protein / creatinine ratio can be correctly assessed for the renal excretion of protein without determining the amount of daily urine output..

     The physiological justification for this approach is as follows: in the same person under stable conditions, urinary creatinine excretion is relatively constant (the amount of creatinine that is produced by the human body during the day is constant, creatinine passes freely through the glomerular filter and is not reabsorbed in the renal tubules, thus, all creatinine formed in the body is excreted in the urine during the day), and its concentration in the urine depends solely on the amount of urine output, which in turn is ISITO on the amount of fluid intake. Similarly, the amount of diuresis affects the protein concentration in the urine, while the ratio of protein to creatinine remains constant for any amount of diuresis.

    Let us give an example of individual variations in the concentration of protein and creatinine in urine in one of the practically healthy subjects. The morning urine sample was examined for 7 days. The studies were carried out using the analytical system: URiSCAN-BK protein and creatinine analyzer in urine, Uni-Test-BM reagent kit (for protein in urine) and UTS creatinine reagent kit (for determination of creatinine in urine and serum). The results are presented in Table 1.

Table 1. Individual variations in protein and creatinine concentrations.

      As can be seen from the data presented, the spread of protein concentration in the urine is more than 10 times (from 0.013 to 0.166 g / l)! 09/13. the subject drank 3 glasses of water at night, which significantly increased the volume of morning urine output and the protein concentration in the urine was 0.013 g / l, and on September 19 there was the opposite situation - the liquid was not taken before bedtime, which led to a significant concentration of the morning urine and an increase in protein concentration almost 13 times (0.166 g / l). A similar dependence was revealed for creatinine (creatinine concentration changed 6.4 times), which indicates the presence of a common reason for such significant concentration variations of the studied analytes. In this case, this is the volume of urine output. The ratio of protein / creatinine remains relatively constant - it has changed only 1.9 times.

     In numerous clinical studies, it was found that the protein-creatinine ratio in the first morning urine dose clearly correlates with the level of daily proteinuria. So, the ratio of protein / creatinine more than 3.0-3.5 g of protein / g of creatinine corresponds to the excretion of protein above 3.0-3.5 g / day, less than 0.2 g of protein / g of creatinine - a level below 0.2 g /day. Therefore, in all current Russian and foreign clinical guidelines for the diagnosis of proteinuria, it is recommended to determine the ratio of total protein / creatinine and albumin / creatinine.

     Normally, the ratio of total protein / creatinine from various sources does not exceed 0.15-0.2 g of protein / creatinine, with tubulointerstitial kidney damage (impaired reabsorption), this indicator is in the range from 0.2 g / g to 1.0 g / g, with glomerular diseases (impaired barrier function) exceeds 1.0 g / g, and with severe preeclampsia it can reach 5.0 g protein / g creatinine or more.

     Read more about modern approaches to the diagnosis of proteinuria in the article: Diagnosis of proteinuria. To help a practitioner. A.N. Shibanov, O.A. Kurilyak