Very low urinary sodium excretion

Introduction Very low urinary sodium output is a significant clinical manifestation of hyponatremia. The normal value of blood sodium is 142 mmol/L (135-145 mmol/L), and the sodium level below 135 mmol/L is hyponatremia. Urine sodium content: normal adult 70 ~ 90mmol / 24h, about sodium chloride 4.1 ~ 5.3g. If the urine Na+<34.19mmol/L or absent, it indicates that Na+ is absent in the body. Hyponatremia is a common electrolyte disorder in the clinic. The loss of body fluids is often accompanied by the loss of water with certain solutes (electrolytes). Therefore, sodium and water are closely related and interdependent.

Cause

Etiology classification

There are many methods for classification. The changes in extracellular fluid volume are not considered from hyponatremia. The more complete causes are classified as:

(a) sodium loss hyponatremia

Loss of sodium is accompanied by loss of water, but the loss of salt is greater than the loss of water through the intake of water or the compensation of the body. Therefore, sodium hyponatremia is hypotonic, including hypotonic dehydration, ie hyponatremia. There is a decrease in the capacity of extracellular fluid. Common in vomiting, diarrhea, gastrointestinal drainage, large loss of gastrointestinal digestive juice, a lot of sweating, severe burns, large amount of exudate, drainage of pleural effusion, ascites, renal dysfunction, adrenal insufficiency, ADH secretion abnormal syndrome, diabetes Acidosis, a large number of diuretics and so on.

(two) dilute hyponatremia

Refers to excessive water retention in the body, the overall amount of water is too much, the total amount of sodium in the body does not change or slightly increase, due to blood dilution and manifested hyponatremia, which is also hypotonic. Common in mental polydipsia, patients drink plenty of water, the kidneys are too late or can not be completely discharged; brain diseases, malignant tumors, lung lesions and surgical, trauma and other stress stimuli, abnormal increase in ADH secretion; and hypothyroidism, etc. . The blood volume of patients with dilute hyponatremia can be slightly increased, so the urine sodium is not reduced. The osmotic pressure of >20mmol / L can be reduced from normal 285 mmol / L to 240 mmol / L, and serum sodium is usually 130 ~ 140. Mmmol / L or lower.

(3) Increased total amount of hyponatremia sodium

This primary factor is sodium retention, while water retention > sodium retention, and lead to lower blood sodium, also known as expansive hyponatremia. Common in congestive heart failure, cirrhosis, decompensation, nephrotic syndrome and acute, chronic renal failure. This type of hyponatremia is mostly gradual and often maintains a new balance under certain hypotonic conditions. Patients often have hypokalemia, hypoproteinemia, low urine output, high urine and normal potassium, and high urine relative density.

(4) Asymptomatic hyponatremia

Mainly seen in chronic wasting diseases such as severe tuberculosis. Advanced cancer, cachexia, malnutrition, etc., this mechanism is not clear, so it is called idiopathic hyponatremia. The nomenclature of asymptomatic hyponatremia is inadequate because many cases of early or slow progression of hyponatremia are asymptomatic.

(5) pseudohyponatremia

Hyperlipidemia, hyperproteinemia such that a large amount of highly permeable substances such as hyperglycemia and mannitol are present in the blood. The blood sodium concentration is lowered, which is called pseudohyponatemia. In general, when the total serum lipid is 60 g/L or the total serum protein is 140 g/L, the blood sodium concentration is reduced by about 5%.

(6) Cerebral salt loss syndrome

Caused by hypothalamus or brain stem injury, leading to neurological regulation of the kidney, osmotic diuresis in the distal tubules, increased sodium, chlorine, and potassium in the urine, and decreased in the blood. Clinically, hyponatremia is sometimes a single cause, but it is often complex. When analyzing the etiology and pathogenesis of hyponatremia, it needs to be fully understood and considered.

For the treatment of hyponatremia and dilute hyponatremia, see "hypotonic water loss", "excessive water and water poisoning". Therapeutic hyponatremia is mainly for the treatment of primary disease.

mechanism

The loss of body fluid is often accompanied by the loss of water with certain solute (electrolyte). For example, diarrhea can cause a large amount of digestive juice to be lost. The digestive juice is basically isotonic. Although the loss of isotonic fluid does not directly cause hypotonicity or low sodium. Hypertension, but reduced blood volume can cause thirst, after inhalation or infusion of hypotonic fluid, hypotonic or hyponatremia occurs. The first cause is extracellular fluid hypotonic. The main reaction of the body during hypotonic is water diuretic to discharge excess water. The discharge of water is mainly done by the kidney. The mechanism is:

1 The supra-nuclear osmotic pressure receptor receives stimulation, which reduces the release of ADH in the posterior pituitary.

2 There is enough liquid to be filtered out through the glomerulus and reach the dilution section of the renal tubule, ie the ascending branch of the myelin and the distal convoluted tubule.

3 The function of the tubule dilution section is normal, and the reabsorption of sodium is ensured by the action of aldosterone. Since ADH reduces the permeability of the distal renal tubular epithelial cells to water, the water absorption is reduced. As a result, a large amount of moisture is discharged. The kidney's drainage capacity can reach 15-20L per day. Kidney regulation of water and sodium is essential. If any cause causes urinary dilution disorder, such as abnormal increase in ADH release, glomerular filtration reduction, and impaired renal dilution function, water will be stored in the body. On the other hand, hypotonic extracellular fluid will inevitably lead to the exchange of fluid between the intracellular fluid and the extracellular fluid, and maintain a new balance. Because the kidneys are against water. The regulation and mobilization of salt metabolism requires a certain period of time. Therefore, the extracellular fluid is seriously hypotonic or the water is stored too fast, which will cause the extracellular fluid to transfer a large amount of water into the cells, causing intracellular edema (water poisoning).

an examination

Related inspection

Urine routine filtration of sodium excretion fraction FENa serum sodium (Na+, Na)

Plasma osmotic pressure (POP) -- Plasma osmolality (POP) refers to the number of molecules (mg) per kilogram of water, clinically expressed in mOsm / (kg? H2O) or mmol / L, mainly with plasma The concentration of sodium ions is related.

Glycated hemoglobin component (GHb, HbA1c) - Glycated hemoglobin (GHb) refers to the portion of hemoglobin in the blood that is bound to glucose. When the blood glucose concentration is high, the glycated hemoglobin content formed by the human body will be relatively high. The life span of red blood cells in humans is generally 120%. Before the cells die, the glycated hemoglobin content in the blood will remain relatively unchanged. Because of the saccharification, the erythrin level reflects the average blood glucose level within 120 days before the test, and it has nothing to do with whether the blood is taken, whether the patient is fasting, whether insulin is used or not. It is a good indicator for determining long-term control of diabetes.

Glycosylated serum protein (GSP) -- Glucose in the blood reacts with the non-enzymatic glycation of albumin and other protein molecules N to form glycated serum proteins. Since the half-life of albumin in serum is about 21 days, the determination of glycated serum protein can effectively reflect the average blood glucose level of patients in the past 1-2 weeks, and is not affected by the blood glucose concentration at that time. It is a good indicator for glycemic control in diabetic patients. .

Differential diagnosis

There are more urinary porphyrins in the urine: it is caused by porphyria. Porphyria is a disorder of porphyrin metabolism disorder characterized by increased excretion of porphyrin and porphyrin precursors in urine and feces. Porphyria is a congenital disease that is mainly caused by a lack of various enzymes involved in heme synthesis and has a family history.

Increased urinary estrogen: Determination of estrogen in urine: There are three main types of estrogen in the urine, namely estrone, estradiol and estriol. Estrogen has different normal values in different stages of menstrual cycle in women of childbearing age. In the first 7 days of menstrual cycle, estrogen levels are very low, and then rise with the development of follicles, reaching a peak on the 13th day, called ovulation peak. After a sudden decline, it gradually rose, and reached the peak on the 21st day, called the peak of the corpus luteum. Later, it will drop to menstrual cramps. Functional uterine bleeding estrogen levels are maintained below normal levels. The level of estrogen in uterine amenorrhea is normal, but the ovarian function is defective or the congenital ovary is not developed and causes amenorrhea. The estrogen level is low, but there is no periodic change. The pituitary or subthalamic amenorrhea, the estrogen level is generally lower. .

Persistent sodium excretion in the urine: belongs to the antidiuretic hormone abnormal syndrome (SIADH), which means that when the plasma osmotic concentration and blood sodium are normal or low, the vasopressin is still secreted, resulting in a decrease in free water clearance, water retention, and low A syndrome of a series of clinical manifestations such as sodiumemia, hypotonic blood pressure, and the like. In addition to the primary disease manifestations, SIADH children are parallel with the degree of hyponatremia. When serum sodium is above 120mmol/L, the clinical symptoms are asymptomatic. When the blood sodium drops below 120mmol/L, there may be loss of appetite and nausea. Symptoms such as vomiting, when the urine sodium content is high, blood sodium is lower than 110mmol / L, neuropsychiatric symptoms, even convulsions, coma until death, when blood sodium is lower than 95 ~ 109mmol / L, for 3 days can cause irreversible Brain Injury.

Increased histamine excretion in the urine: Histamine is a reactive amine compound with a chemical formula of C5H9N3 and a molecular weight of 111. As a chemical conductive substance in the body, it can affect the reaction of many cells, including allergies, inflammatory reactions, gastric acid secretion, etc. It can also affect the nerve conduction in the brain, which can cause sleep and other effects. The metabolites after taking H1 receptor antagonists (ie, antihistamines) are excreted in the kidneys for a few to several tens of hours, and the urine excretion accounts for a large part. This leads to an increase in histamine excretion in the urine.

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