Dr. Chandra Mauli Jha (CMJ), from the Burjeel Hospital in Abu Dhabi, United Arab Emirates, discusses his abstract for the National Kidney Foundation’s 2016 Spring Clinical Meetings (SCM16), Hyponatremia: Proposed New Classification Based on Urine Osmolarity & Pathophysiology, with Dr. Kenar Jhaveri, AJKD Blog Editor.
AJKDblog: Why don’t you tell us a little about your research and abstract being presented at NKF 2016 Spring Meetings?
CMJ: Hyponatremia remains a common clinical problem managed by physicians of different specialties. Present prevalent classification of hypotonic hyponatremia is primarily based on consideration of urine osmolarity and volume status of the patient. Syndrome of inappropriate antidiuretic hormone (SIADH) is considered in this classification if the patient is euvolemic and urine osmolarity is greater than 100 mOsm/kg. This approach rests on the assumption that urine would be maximally diluted (<100 mOsm/Kg) when vasopressin is not acting upon the medullary collecting duct (MCD). It neglects the fact that urine osmolality usually exceeds the plasma osmolality when vasopressin acts upon MCD. We feel that in such patients, there is a range of urine osmolarity (100-300 mOsm/kg), which is thought to be caused by vasopressin action, though this may not be true in all cases. This results in a lower threshold of diagnosing SIADH, which has led to over diagnosis of the condition and a missed opportunity of correcting diagnoses in patients with hypotonic hyponatremia whose urine osmolality lies within 100-300 mOsm/kg.
Our proposed classification approaches the problem in the initial step by comparing the urine osmolarity with plasma osmolarity. It classifies hypotonic hyponatremia into two broad groups: 1) hypotonic hyponatremia with urine osmolarity lesser than plasma osmolarity, and 2) hypotonic hyponatremia with urine osmolarity greater than plasma osmolarity. Patients in the first group could have conditions involving decreased filtrate delivery to the distal nephron or a change in residual water permeability of the distal nephron in which ADH has no role to play. They also might have conditions like hyper-responsive state to ADH or reset osmostat state in which vasopressin mechanisms do not operate.
AJKDblog: Can you give us an example on how this can help in classifying and treating a patient?
CMJ: The proposed classification would not change the acute management of life threatening hyponatremia. But it would have an impact on the management of chronic hyponatremia and on prevention in patients with recurrent hospitalization for hyponatremia.
We have highlighted the benefit of our proposed system in another poster, Polyuria in a Patient with Hyponatremia: Residual Water Permeability – A Conceptual Explanation, which will also be presented by our group at the NKF 2016 Spring Meetings. The reference patient had repeated hospitalizations for chronic hyponatremia. She was an elderly, diabetic, hypertensive woman who had hysterectomy for poorly differentiated adenocarcinoma. She also received combined chemotherapy and radiotherapy for gingival carcinoma. Employing the proposed approach, we could consider the diagnosis of reset osmostat with primary polydipsia. The diagnosis of reset osmostat would prevent the patient from unnecessary hospitalizations, for example, whenever she might present at a health facility and her plasma sodium is noted low yet higher than the reset value.
AJKDblog: Where do you and your group go from here?
CMJ: We would be interested in checking the validity and utility of our proposed classification system. Our group has planned to maintain a record of hyponatremic patients in our clinical practice during the next year, followed by an analysis to determine if we would have reached the same diagnoses if we had applied the classical approach.
After the Spring Clinical Meetings, we also intend to share our proposed system with our local nephrology colleagues, with whom we meet every two months. We will urge them to check the validity of our system and share their experiences.
All Spring Clinical Meeting abstracts are available in the May issue of AJKD.