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 Q1. –What are the solid components of urine in normal health?

Answer-Urine is a fluid composed of water (95%), inorganic and organic solids (5%) which include:

A) Chief inorganic solids :- Sodium, Potassium, Chlorides,

In addition, smaller amounts of calcium,magnesium, sulphate and phosphates, and traces of iron, copper, zinc and iodine.

B) Chief organic solids :

1. Non-protein nitrogen (NPN) compounds like-urea,uric acid, creatinine and amino acids

2. Organic acids   

3. Sugars.

4. In addition, traces of proteins, vitamins, hormones and pigments are also present in the urine.

Q.2- What kind of abnormal components are present in urine in different diseased  states?

Answer- Under different conditions proteins, reducing sugars, ketone bodies, blood, bile pigments, bile salts, lymph or fat may be there in urine. These substances are present in urine in normal health also but only in very minute concentration and hence cannot be detected by routine laboratory procedures. In different diseases their excretion is grossly increased and hence can be easily detected by conventional methods. So it is abnormal concentration which makes them abnormal constituents.

Q.3- What is the amount of urea excreted per day? What are the causes of decreased urea excretion in urine?

Answer- Approximately 15-40 g of urea is excreted per day in normal health. Urinary urea is decreased mainly in renal failure, but it can also be decreased in patients on low protein diet, in growing period (amino acids are needed for active protein synthesis in growing period, so amino group is not available for urea formation, in fact all conditions of positive nitrogen balance like pregnancy, recovery from illness, repair etc. will lower down urinary urea levels). Since urea is formed in liver and excreted through kidneys, hence in liver diseases, urea formation can be impaired, and thus urinary urea level will also be low.

In renal failure blood urea is high but urinary urea is low due to failure of excretion, while in other conditions of positive nitrogen balance and cirrhosis of liver, blood urea is also low.

In contrast urinary urea is high in conditions of negative nitrogen balance or when the body is in a state of catabolism as in starvation, chronic infections, hyperthyroidism, cancers etc. Most importantly decreased urea excretion in the presence of high blood urea level carries most practical attention, since these two features depict impaired functional status of the kidney.

Q.4- What do you expect the level of urinary uric acid in a patient suffering from gout?

Answer- Uric acid is a normal component of urine. Its concentration may be decreased or may be normal in gout depending upon the type of gout. Hyperuricemia in gout may be due to increased formation or due to impaired excretion of uric acid. In renal disease or when there is excessive load of lactate or ketone bodies uric acid is retained (Lactate and ketone bodies share a common transporter- organic acid transporter in the kidney for reabsorption in the renal tubule, hence when excess lactate or ketone bodies are there in filtrate, uric acid is reabsorbed while lactate and ketone bodies are excreted out)), Excess formation of uric acid takes place in various congenital or metabolic defects. In these conditions excretion is not much affected.

Q.5- A 67- year-old male has been hospitalized due to chronic renal failure. He is a known diabetic and hypertensive.  His blood and urine samples have been sent to the laboratory for confirmation of diagnosis. What are the markers of renal failure in blood and urine?

Answer- In renal failure the substances which are normally excreted by the kidney in urine are not excreted and are retained in blood. It can be well presumed that urea, uric acid and creatinine (normal urinary solid components) would be low in urine but would be high in blood. These three parameters – urea, uric acid and creatinine serve as markers of renal failure. Based on the same facts of impaired excretion in renal failure- urea and creatinine clearance are undertaken to determine the functional status of the kidney.

Q.6-What is the source of sulphates in urine?

Answer- Urinary sulphates are derived from sulphur-containing vitamins and amino acids. The sulphur-containing vitamins are-Lipoic acid, Thiamine and Biotin, while Cysteine, Cystine, Methionine and Homocysteine are sulphur-containing amino acids.

Q.7- What are the sources of phosphates in urine?

Answer- Phospholipids, phosphoproteins, nucleic acids and nucleotides contribute phosphates to urine. Phosphates are also derived from demineralization of bones. In hyperparathyroidism and rickets urinary phosphates are increased, while in hypoparathyroidism and renal diseases urinary phosphates are decreased.

Q.8-What is the source of Hippuric acid in urine?

Answer- Hippuric acid is formed in the liver by conjugation reaction. Benzoic acid conjugates with Glycine to form Hippuric acid which is excreted in urine. This reaction takes place exclusively in liver. Hippuric acid excretion test is undertaken by giving a loading dose of sodium benzoate to determine the functional status of the liver. Kidney functions should be normal for this test. In liver diseases Hippuric acid excretion is deceased.

Q.9- Whatis creatinuria?

Answer-Creatine is a precursor of creatinine and upon losing one molecule of water, creatine is converted to creatinine. So creatinine is an anhydrous from of creatine. This is a nonenzymatic spontaneous conversion. Creatine is not normally excreted in urine,it is creatinine which is there in urine. But in certain conditions, creatine is excreted excessively in urine and this state is termed as creatinuria. The causes for this are- Hyperthyroidism, Myasthenia gravis, pregnancy, infancy,uncontrolled diabetes mellitus, growing period, starvation and muscular  diseases.

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