#5026 ESTIMATED PROXIMAL TUBULE FLUID PHOSPHATE CONCENTRATION AS AN ELEMENT OF DECREASED RENAL FUNCTION IN PATIENTS UNDERGOING UNILATERAL NEPHRECTOMY
Authors: Tartaglione Lida , Rotondi Silverio , Franco Francesca , Pasquali Marzia , Tinti Francesca , Mazzaferro Sandro 
Published: June 2023

Abstract

Background and Aims
Patients with chronic renal failure (CRF) develop early alterations in mineral metabolism called Chronic Kidney Diseases Mineral Bone Disorders (CKD-MBD), detectable with the available markers (PTH, Ca, Ps) only in the most advanced stages of disease. Recent evidence suggests that the early development of CKD-MBD is related to the nutritional phosphorus intake and the reduction of the number of nephrons (renal functional reserve). Infact with the reduction in the nephrons number, compensation systems must be activated for the maintenance of the phosphoric balance with an increase in urinary phosphate and in the concentration of phosphorus in the single nephron (ePTFp). Therefore, the measurement of ePTFp has been proposed as a new early marker of CKD-MBD and effective renal functional reserve. Threshold values of ePTFp (2.2 mg/dl) have been identified to indicate patients with reduced renal functional reserve and therefore at increased risk of progression of renal damage. The measurement of residual renal function with ePTFp may be a useful parameter to be evaluated in patients who undergo unilateral nephrectomy due to renal neoplasia. In fact, post-nephrectomy some patients have a high reduction of the renal function not identified by preoperative GFR assessment or other risk factors. In these patients, ePTFp could represent a measure of pre nephrectomy kidney functional reserve and thus indicate the risk of reduce renal function after nephrectomy. The aim of the study was to evaluate the relationship between pre-operative ePTFp and renal function after nephrectomy.

Methods
This is a transversal monocentric observational study. From January 2022 to November 2022, we enrolled patients diagnosed with renal cell carcinoma for which has been indicated unilateral nephrectomy surgery. In all patients we evaluated pre nephrectomy and three months after surgery, renal function, and ePTFP with the formula [ePTFp = (Phosphaturia / creati-ninuria) x creatininemia x 3,33]. 30 subjects with normal renal function (eGFR 100±10 ml/min, no proteinuria) were evaluated for the ePTFp reference values.

Results
We evaluated 13 patients: age 57.5 ± 13.6; Cr 1.48±0.7 mg/dl; eGFR 58.5 ± 23.3, mil/min; Pi, mg/dl 3.2± 0.6; Ca 9.9± 0.6 mg/dl,PTH 58,8± 41 pg/ml FA 176,7± 108 IU/L, proteinuria 500±150 mg 24H. Compared to the control population (GFR 100 ml/min) the 24-hour phosphaturia was no different while ePTFp was increased 2.1± 0.9 vs 1.2±0.2 mg/dl; p: 0.05. In the post-nephrectomy assessment, creatinine and GFR were stable (Cr 1.48±0.7 vs 1.5 ±0.7 mg/dl; p: n.s; eGFR 58.5 ± 23.3, vs 56.5 ± 22.3, mil/min; p: n.s), while ePTFp was increased (ePTFp pre 2.1± 0.9 vs ePTFp post 3.3± 2.7; p&lt;0.01). Patients with pre-nephrectomy ePTFP ≥ 2.2 mg/dl (n. 6, eGFR 56.5 ± 20.3, proteinuria 550±100 mg/24h) had a greater renal function reduction post nephrectomy (mean GFR delta -9.5±2 ml/min) respect to patients with pre-nephrectomy ePTFP &lt;2.2 mg/dl (n. 7, eGFR 59.7 ± 24.3, proteinuria 500±200 mg/24h; mean GFR delta -0.5±2 ml/min; p: 0.05). In all the population there was direct correlation between ePTFp and the reduction of GFR post nephrectomy (r: 0.667; p: 0.05).

Conclusion
In our patients ePTFp was higher than the control group and correlate with the entity of the GFR reduction post nephrectomy. The group with a preoperatory ePTFp ≥ 2,2 mg/dl had a higher post nephrectomy GFR reduction. These results suggest that ePTFp identify the pre nephrectomy kidney functional reserve. In particular and ePTFp higher than limits highlighted in the literature (2.2 mg/dl) pre nephrectomy identify a greater risk of kidney function reduction post nephrectomy. ePTFp may be proposed as a parameter to identify patients with higher risk of decreased renal function post nephrectomy.