Urine Analysis and Health Diagnosis | 尿液分析与健康诊断

📚 Urine Analysis and Health Diagnosis | 尿液分析与健康诊断

Urine analysis, or urinalysis, is one of the oldest and most widely used diagnostic tools in clinical medicine. It involves the physical, chemical, and microscopic examination of urine to detect metabolic abnormalities, kidney disorders, and systemic diseases. For A-Level Biology students, understanding how urine is produced and how its composition reflects physiological and pathological states is essential.

尿液分析（urinalysis）是临床医学中最古老且最广泛使用的诊断工具之一。它通过对尿液进行物理、化学和显微镜检查，来检测代谢异常、肾脏疾病和全身性疾病。对于A-Level生物学生而言，理解尿液如何生成以及其成分如何反映生理和病理状态，是考试的核心要求。

1. Formation of Urine | 尿液的生成

Urine is formed in the nephron through three main processes: ultrafiltration in the glomerulus, selective reabsorption in the proximal convoluted tubule (PCT), and secretion in the distal convoluted tubule (DCT) and collecting duct. Blood pressure forces water, glucose, amino acids, urea, and inorganic ions through the glomerular filtration barrier, while blood cells and large proteins remain in the capillaries.

尿液在肾单位中通过三个主要过程生成：肾小球的超滤（ultrafiltration）、近曲小管（PCT）的选择性重吸收（selective reabsorption），以及远曲小管（DCT）和集合管的分泌作用。血压将水、葡萄糖、氨基酸、尿素和无机离子压过肾小球滤过屏障，而血细胞和大分子蛋白质则留在毛细血管中。

The composition of glomerular filtrate is very similar to blood plasma, except that it lacks cells and large proteins. As the filtrate passes along the nephron, essential substances such as glucose and amino acids are actively reabsorbed, while the concentration of waste products like urea increases in the urine.

肾小球滤液的成分与血浆非常相似，只是不含细胞和大分子蛋白质。当滤液沿肾单位流动时，葡萄糖和氨基酸等必需物质被主动重吸收，而尿素等代谢废物的浓度在尿液中逐渐升高。

2. Normal Composition of Urine | 尿液的正常成分

Normal urine consists of approximately 95% water. The remaining 5% contains dissolved solutes, including urea (from protein metabolism), uric acid (from nucleic acid metabolism), creatinine (from muscle metabolism), inorganic ions such as sodium (Na⁺), potassium (K⁺), chloride (Cl⁻), and small amounts of other substances.

正常尿液约含95%的水。其余5%含有溶解的溶质，包括尿素（来自蛋白质代谢）、尿酸（来自核酸代谢）、肌酐（来自肌肉代谢）、钠离子（Na⁺）、钾离子（K⁺）、氯离子（Cl⁻）等无机离子，以及少量其他物质。

• Water: ~95% | 水：约95%

• Urea: ~2% | 尿素：约2%

• Inorganic ions (Na⁺, K⁺, Cl⁻, Ca²⁺, Mg²⁺) | 无机离子（Na⁺、K⁺、Cl⁻、Ca²⁺、Mg²⁺）

• Other organic solutes: uric acid, creatinine | 其他有机溶质：尿酸、肌酐

Glucose, protein, and blood cells are normally absent or present in only trace amounts in healthy urine. Their presence in significant quantities usually indicates a pathological condition.

健康人的尿液中通常不含葡萄糖、蛋白质和血细胞，或仅含微量。若这些物质大量出现，通常提示存在病理状况。

3. Physical Examination: Colour and Turbidity | 物理检查：颜色与混浊度

The physical examination of urine begins with observing its colour and clarity. Normal urine ranges from pale yellow to deep amber, a colour imparted by the pigment urochrome, which is derived from the breakdown of haemoglobin. The intensity of the colour varies with the concentration of the urine—more concentrated urine appears darker.

尿液物理检查首先观察其颜色和清澈度。正常尿液呈淡黄色至深琥珀色，这种颜色来自尿色素（urochrome），它源于血红蛋白的分解。颜色的深浅随尿液浓度变化——尿液越浓缩，颜色越深。

• Pale yellow / clear: normal, well-hydrated | 淡黄色/清澈：正常，水分充足

• Dark amber: dehydration, concentrated urine | 深琥珀色：脱水，尿液浓缩

• Red or pink: blood (haematuria), certain foods or drugs | 红色或粉色：血液（血尿）、某些食物或药物

• Turbid / cloudy: infection (pus), phosphate crystals | 混浊/云雾状：感染（脓液）、磷酸盐结晶

Cloudy urine may suggest a urinary tract infection (UTI), where white blood cells and bacteria accumulate in the urine. Conversely, very foamy urine can indicate the presence of protein, a condition known as proteinuria.

尿液混浊可能提示泌尿道感染（UTI），此时尿液中聚集了白细胞和细菌。相反，尿液出现大量泡沫则可能表示尿中含有蛋白质，即蛋白尿（proteinuria）。

4. Chemical Test: Glucose (Benedict’s Test) | 化学检测：葡萄糖（本尼迪克特试验）

In healthy individuals, the glucose filtered by the glomerulus is completely reabsorbed by the proximal convoluted tubule via co-transport with sodium ions. Therefore, glucose is normally absent from the urine. However, when the blood glucose concentration exceeds approximately 180 mg/dL (10 mmol/L)—the renal threshold—the carrier proteins become saturated, and glucose spills into the urine, a condition called glycosuria.

在健康人体内，肾小球滤出的葡萄糖通过近曲小管与钠离子协同转运被完全重吸收。因此，尿液中通常不含葡萄糖。然而，当血糖浓度超过约180 mg/dL（10 mmol/L）——即肾阈值（renal threshold）时，载体蛋白达到饱和，葡萄糖便溢出进入尿液，这种情况称为糖尿（glycosuria）。

Benedict’s test is used to detect reducing sugars such as glucose in the urine. When an equal volume of Benedict’s reagent is added to a urine sample and heated, the colour change indicates the concentration of glucose:

本尼迪克特试验用于检测尿液中的还原糖（如葡萄糖）。将等体积的本尼迪克特试剂加入尿液样品并加热后，颜色变化可以指示葡萄糖的浓度：

Glycosuria is most commonly associated with diabetes mellitus, but can also occur temporarily after a very high-carbohydrate meal, during pregnancy, or due to emotional stress (stress glycosuria).

糖尿最常见于糖尿病（diabetes mellitus），但也可能是摄入大量碳水化合物后、妊娠期间，或情绪紧张（应激性糖尿）引起的一过性现象。

5. Chemical Test: Protein (Biuret Test) | 化学检测：蛋白质（双缩脲试验）

The glomerular filtration barrier normally prevents large plasma proteins (e.g., albumin) from entering the filtrate because their molecular mass exceeds the size of the filtration pores. However, when the basement membrane of the glomerulus is damaged—as in glomerulonephritis or nephrotic syndrome—proteins pass into the filtrate and appear in the urine.

肾小球滤过屏障通常阻止血浆大分子蛋白质（如白蛋白）进入滤液，因为这些蛋白质的分子质量超过滤过孔的大小。然而，当肾小球基底膜受损时——如肾小球肾炎（glomerulonephritis）或肾病综合征（nephrotic syndrome）——蛋白质进入滤液并出现在尿液中。

Proteinuria can be detected using the biuret test. A few drops of sodium hydroxide (NaOH) solution are added to the urine sample, followed by a few drops of dilute copper(II) sulphate (CuSO₄) solution. If protein is present, the solution turns from blue to purple. The intensity of the purple colour is proportional to the protein concentration.

蛋白尿可用双缩脲试验检测。向尿液样品中加入几滴氢氧化钠（NaOH）溶液，然后加入几滴稀硫酸铜（CuSO₄）溶液。如果存在蛋白质，溶液会从蓝色变为紫色。紫色的深浅与蛋白质浓度成正比。

Protein (peptide bonds) + CuSO₄ in NaOH → purple complex

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