Plasma arginine vasopressin and atrial natriuretic peptide concentration in patients with hyponatremia at diagnosis and following treatment

Copeptin in fluid disorders and stress

Copeptin, a glycosylated peptide of 39 amino acids, is the C-terminal segment of arginine vasopressin (AVP) precursor peptide, which is consisted of two other fragments, vasopressin and neurophysin Ⅱ. The main physiological functions of AVP are fluid and osmotic balance, cardiovascular homeostasis and regulation of the endocrine stress response. Numerous studies have demonstrated that the endogenous AVP in plasma is a meaningful biomarker to guide diagnosis and therapy of diseases associated with fluids disorders and stress. However, due to its instability, short half-time life in circulation and lack of readily available AVP assays, clinical measurement of AVP is restricted. In contrast to AVP, copeptin which is released in an equimolar mode with AVP from the pituitary, has emerged as a stable and simple-to-measure surrogate marker of AVP and displays excellent potential in diagnosis, differentiation and prognosis of various diseases. This review will discuss the studies on the clinical value of copeptin in different diseases, especially in AVP-dependent fluids disorders, as well as issues and prospects of the application of this potential biomarker.

Mid-regional pro-atrial natriuretic peptide and the assessment of volaemic status and differential diagnosis of profound hyponatraemia

BACKGROUND

Hyponatraemia is common and its differential diagnosis and consequent therapy management is challenging. The differential diagnosis is mainly based on the routine clinical assessment of volume status, which is often misleading. Mid-regional pro-atrial natriuretic peptide (MR-proANP) is associated with extracellular and cardiac fluid volume.

METHODS

A total of 227 consecutive patients admitted to the emergency department with profound hypo-osmolar hyponatraemia (Na < 125 mmol L(-1) ) were included in this prospective multicentre observational study conducted in two tertiary centres in Switzerland. A standardized diagnostic evaluation of the underlying cause of hyponatraemia was performed, and an expert panel carefully evaluated volaemic status using clinical criteria. MR-proANP levels were compared between patients with hyponatraemia of different aetiologies and for assessment of volume status.

RESULTS

MR-proANP levels were higher in patients with hypervolaemic hyponatraemia compared to patients with hypovolaemic or euvolaemic hyponatraemia (P = 0.0002). The area under the curve (AUC) to predict an excess of extracellular fluid volume, compared to euvolaemia, was 0.73 [95% confidence interval (CI) 0.62-0.84]. Additionally, in multivariate analysis, MR-proANP remained an independent predictor of excess extracellular fluid volume after adjustment for congestive heart failure (P = 0.012). MR-proANP predicted the syndrome of inappropriate antidiuresis (SIAD) versus hypovolaemic and hypervolaemic hyponatraemia with an AUC of 0.77 (95% CI 0.69-0.84).

CONCLUSION

MR-proANP is associated with extracellular fluid volume in patients with hyponatraemia and remains an independent predictor of hypervolaemia after adjustment for congestive heart failure. MR-proANP may be a marker for discrimination between the SIAD and hypovolaemic or hypervolaemic hyponatraemia.

Hyponatremia may reflect severe inflammation in children with febrile urinary tract infection

BACKGROUND

Hyponatremia is the most common electrolyte abnormality in clinical practice, but little is known about the association between febrile urinary tract infection (UTI) and hyponatremia or its significance to clinical outcomes.

METHODS

Data from 140 children with febrile UTI between 2000 and 2010 were retrospectively analyzed. Laboratory examinations [white blood cell (WBC) count, erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and serum sodium concentration], renal ultrasonography, (99m)Technetium-dimercaptosuccinic acid (DMSA) scintigraphy, and voiding cystourethrogram were performed. Culture growing >50,000 colonies of one single bacterial species on a urine sample obtained by catheter or >100,000 colonies on two clean-catch samples was required to establish diagnosis of UTI.

RESULTS

In children with renal cortical defects diagnosed after DMSA scintigraphy (group 1), duration of fever was significantly longer (P = 0.038) and WBC (P = 0.047) and CRP (P < 0.0001) levels significantly higher than in those without renal cortical defects (group 2). However, serum sodium levels were significantly lower in group 1 than group 2 (135.9 ± 2.4 vs 137.4 ± 2.7 mEq/L, P = 0.007). Hyponatremia (serum sodium ≤ 135 mEq/L) was also more frequent in group 1 than in group 2 (74.1 % vs 45.3 %, P = 0.012). Serum sodium concentration was negatively correlated with WBC count (r = -0.156, P = 0.011) and CRP levels (r = -0.160, P= 0.028).

CONCLUSIONS

Our study indicates that hyponatremia may be a substantial inflammatory marker and is significantly and independently associated with the degree of inflammation in children with febrile UTI.

Hyponatremia in neurosurgical patients: clinical guidelines development

OBJECTIVE

Neurosurgical patients have a high risk of hyponatremia and associated complications. We critically evaluated the existing literature to identify the determinants for the development of hyponatremia and which management strategies provided the best outcomes.

METHODS

A multidisciplinary panel in the areas of neurosurgery, nephrology, critical care medicine, endocrinology, pharmacy, and nursing summarized and classified hyponatremia literature scientific studies published in English from 1950 through 2008. The panel's recommendations were used to create an evaluation and treatment protocol for hyponatremia in neurosurgical patients at the University of Florida.

RESULTS

Hyponatremia should be further investigated and treated when the serum sodium level is less than 131 mmol/L (class II). Evaluation of hyponatremia should include a combination of physical examination findings, basic laboratory studies, and invasive monitoring when available (class III). Obtaining levels of hormones such as antidiuretic hormone and natriuretic peptides is not supported by the literature (class III). Treatment of hyponatremia should be based on severity of symptoms (class III). The serum sodium level should not be corrected by more than 10 mmol/L/d (class III). Cerebral salt wasting should be treated with replacement of serum sodium and intravenous fluids (class III). Fludrocortisone may be considered in the treatment of hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm (class I). Hydrocortisone may be used to prevent natriuresis in subarachnoid hemorrhage patients (class I). Hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm should not be treated with fluid restriction (class II). Syndrome of inappropriate antidiuretic hormone may be treated with urea, diuretics, lithium, demeclocycline, and/or fluid restriction (class III).

CONCLUSION

The summarized literature on the evaluation and treatment of hyponatremia was used to develop practice management recommendations for hyponatremia in the neurosurgical population. However, the practice management recommendations relied heavily on expert opinion because of a paucity of class I evidence literature on hyponatremia.

Hyponatremia due to an excess of arginine vasopressin is common in children with febrile disease

Hypotonic fluids are commonly used for treating hospitalized children. However, an excess of arginine vasopressin (AVP) with impaired free water excretion is thought to contribute to the development of hyponatremia in febrile children. The aim of this two-part study was to define the clinical relationship between hyponatremia and excess AVP. In a retrospective study carried out between 2001 and 2005, we found that approximately 17% of the hospitalized patients had hyponatremia [serum sodium (Na) < 135 mEq/l] upon admission and that the ratio of patients with hyponatremia was significantly higher among febrile patients than among afebrile patients. In a subsequent prospective study, we examined 73 hospitalized patients who presented with acute febrile diseases accompanied by hyponatremia (serum Na <134 mEq/l). Almost all of these patients demonstrated excess AVP, defined as high plasma AVP levels (>1 pg/ml). There were no significant relationships between the levels of AVP and other laboratory variables, including serum sodium, serum osmolality, atrial natriuretic peptide, and brain natriuretic peptide. About 30% (22/73) of the patients fulfilled the criteria of the syndrome of inappropriate secretion of antidiuretic hormone. These findings suggest that fever and other nonosmotic stimuli lead directly to excess AVP and hyponatremia. We therefore recommend that isotonic fluids should be used for patients with prolonged fever and hyponatremia.