Value of monitoring urine ammonia at time of biopsy in patients with lupus nephritis

Urinary Ammonium in Clinical Medicine: Direct Measurement and the Urine Anion Gap as a Surrogate Marker During Metabolic Acidosis

Ammonium is the most important component of urinary acid excretion, normally accounting for about two-third of net acid excretion. In this article, we discuss urine ammonium not only in the evaluation of metabolic acidosis but also in other clinical conditions such as chronic kidney disease. Different methods to measure urine NH₄⁺ that have been employed over the years are discussed. The enzymatic method used by clinical laboratories in the United States to measure plasma ammonia via the glutamate dehydrogenase can be used for urine ammonium. The urine anion gap calculation can be used as a rough marker of urine ammonium in the initial bedside evaluation of metabolic acidosis such as in distal renal tubular acidosis. Urine ammonium measurements, however, should be made more available in clinical medicine for a precise evaluation of this important component of urinary acid excretion.

Urine inter‐alpha‐trypsin inhibitor family‐related proteins may serve as biomarkers for disease activity of lupus

Background

Systemic lupus erythematosus (SLE) is a chronic inflammatory disease involving multiple tissues. Inter‐Alpha‐Trypsin Inhibitor (ITI) family proteins have a role in maintaining tissue homeostasis, but their possible clinical significance in the SLE patients has not been reported. The aim of this study was to analyze and verify the expression of ITI‐related proteins in the urine of SLE patients, further explore the features of these proteins in disease activity.

Methods

Based on label‐free proteomics technology and bioinformatics technology, we analyzed the expression of ITI family‐related proteins in the urine of lupus. Subsequently, Western‐blot and targeted proteomics were used to qualitatively and quantitatively verify the expression of these proteins, respectively.

Results

A total of seven ITI family‐related proteins were screened and identified; and six of these proteins were differentially expressed in the urine of SLE patients. Further quantitative analysis showed that the expressions of ITIH2, ECM1, and ITIH5 in urine between active SLE group and stable SLE group were consistent with the preliminary screening results. The expression of ITIH2 and ECM1 in the renal damage group were also consistent with the screening results. Moreover, ITIH2 and ECM1 have a good correlation with disease activity and have a certain correlation with renal damage.

Conclusions

In this exploratory study, we evaluated the expression of ITI family‐related proteins in the urine of SLE and found that urine ITIH2 and ECM1 were closely related to SLE activity, especially kidney damage, providing an experimental basis for further exploration of the potential roles in monitoring lupus and lupus nephritis activity.

Assessing urine ammonium concentration by urine osmolal gap in chronic kidney disease

Acidemia is one of the risk factors for end-stage kidney disease and increases the mortality rate of patients with chronic kidney disease (CKD). Although urinary ammonium (U-NH₄ ⁺ ) is the crucial component of renal acid excretion, U-NH₄ ⁺ concentration is not routinely measured. To estimate U-NH₄ ⁺ , urine osmolal gap (UOG = urine osmolality - [2(Na⁺ + K⁺ ) + urea + glucose]) is calculated and the formula (U-NH₄ ⁺  = UOG/2) has traditionally been used. However, the usefulness of this formula is controversial in CKD patients. We assessed the relationship between U-NH₄ ⁺ and UOG in patients with CKD. Blood and spot urine samples were collected in 36 patients who had non-dialysis-dependent CKD. The mean ± SD age of patients was 72.0 ± 14.8 years, and the mean ± SD serum creatinine and U-NH₄ ⁺ were 2.7 ± 2.3 mg/dl and 9.3 ± 9.2 mmol/L, respectively. A significant relationship was found between UOG/2 and U-NH₄ ⁺ (r = .925, p < .0001). U-NH₄ ⁺ estimated using the UOG was on average higher by 4.7 mmol/L than the measured one. Our results suggested that UOG could be a useful tool in clinical settings, especially in patients with moderate to severe CKD.