Very low urinary sodium excretion is a significant clinical manifestation of hyponatremia. The normal value of blood sodium is 142 mmol/L (135-145 mmol/L), and blood sodium below 135 mmol/L is considered hyponatremia. Urinary sodium volume: normal adult 70-90 mmol/24h, which is about 4.1-5.3 g of sodium chloride. if urinary Na+. Tests needed for very low urinary sodium excretion: 1. Filtration sodium excretion fraction FENa Filtration sodium excretion fraction, also known as FENa, is the measurement of the percentage of glomerular filtration of sodium and urinary excretion of sodium, that is, the percentage of sodium that is filtered by the glomerulus and not reabsorbed by the renal tubules. Calculation formula: Sodium excretion fraction = [(urinary sodium × blood creatinine)/(blood sodium × urinary creatinine)] × 100%; Sodium excretion fraction is the most sensitive index to identify pre-renal acute renal failure and acute tubular necrosis, with a positive rate of 98%. In pre-renal acute renal failure, FENa is significantly reduced due to the relative increase in sodium reabsorption by the tubules, resulting in lower urinary sodium excretion. Acute tubular necrosis, the renal tubules can not absorb Na, so urinary Na excretion is significantly increased. The application of diuretics can increase urinary sodium excretion, so the sodium excretion fraction cannot be relied on as a basis for diagnosis at this time. Sodium excretion fraction is the most sensitive index to distinguish pre-renal acute renal failure from acute tubular necrosis. Abnormal results: FENa (%) is a sensitive indicator to distinguish pre-renal azotemia and acute tubular necrosis, pre-renal azotemia FENa (%) <1, acute tubular necrosis FENa (%) > 2. Between 1 and 2 is a blank area, the former reabsorption of sodium enhanced, so that FENa (%) even down to O.1, the latter are often more than 3. 2, blood routine Blood routine is the most general, the most basic blood test. The most basic blood test. Routine blood tests are usually performed with peripheral blood, such as blood from the fingertips and earlobes. After passing through the blood cell analysis instrument, the computer reports the results, and this item has become a practice of examining patients. Blood consists of two major parts, liquid and tangible cells, and routine blood tests are performed on the cellular part of the blood. Blood has three different functions of cells – red blood cells (commonly known as red blood cells), white blood cells (commonly known as white blood cells), and platelets. Diseases are determined by observing changes in number and morphological distribution. It is one of the common auxiliary tests used by doctors to diagnose the condition.