Dehydration fever is an increase in heat loss through the skin when the room temperature is too high. If the body is not sufficiently hydrated at this time, the blood is concentrated, making it easy for newborns to develop dehydration fever. Frequent dehydration fever needs to go to the hospital for systematic examination to find out the cause of the disease. The following are the specific methods to check dehydration fever. 1, isotonic dehydration laboratory tests (1) blood concentration: red blood cells (RBC), hemoglobin (Hb), hematocrit (HCT), plasma protein concentration increases, or the concentration increases compared to the basic value. However, hemodilution occurs in those who have lost blood. (2) Red blood cell morphology: normal, mean red blood cell volume (MCV), mean red blood cell hemoglobin concentration (MCHC) are normal. (3) Urinalysis: urine sodium and urine chloride concentration and 24h excretion decreased, and urine relative density increased. 2. Hypotonic dehydration blood test indicators (1) Serum sodium concentration: decreased, less than 135 mmol/L. Mostly accompanied by hypochlorhydria, and the degree of decrease of both is generally consistent. Blood potassium concentration may be normal or increased. (2) Plasma crystal osmolarity decreases. (3) Hemoconcentration: increased red blood cell count, hemoglobin, plasma protein and hematocrit are seen. The value is greater when compared to basal values. (4) Erythrocyte edema: increased intraerythrocyte water, increased mean red blood cell volume, and decreased mean red blood cell hemoglobin concentration. (5) Common urine laboratory indicators: ① Urinary sodium concentration: decreased due to extrarenal factors, mostly less than 15 mmol/L, or even not measured; elevated in patients with renal impairment, abnormal regulatory mechanisms or use of diuretics, mostly greater than 20 mmol/L. Urinary electrolytes should be routinely checked in patients with sodium deficiency, because even patients with low sodium due to extrarenal factors may be accompanied by reduced renal reabsorption. The urine electrolytes should be routinely checked in patients with sodium deficiency because even patients with hyponatremia due to extrarenal factors may be accompanied by decreased renal reabsorption, such as the elderly, chronic hypokalemia, and patients on aminoglycosides. (ii) Urine chloride concentration: consistent with changes in urine sodium concentration. (③) Excretion: Decreased in those with extrarenal factors, 24h urinary sodium and urinary chloride excretion is significantly reduced or even not measured.