URINARY CALCULI:

URINARY CALCULI:- A calculus is an abnormal, solid concretion of minerals and salts formed around organic materials and found chiefly in ducts and cysts. 

Urinary calculi of varying sizes can form in any part of the urinary tract. It requires a nucleus on which the crystals are deposited. Increased excretion of a substance coupled with concentrated urine can be a predisposing factor.

The presence of calculus in the urinary tract can obstruct urinary flow, and can cause infection and haematuria which can be associated with renal colic. The calculi may be composed of one or more crystals in the urine with a nucleus made of an organic or a foreign body.

Qualitative Analysis of Renal Calculus

Reagents

1. Concentrated nitric acid

2. Concentrated ammonia solution

3. Dilute ammonium hydroxide: Dilute reagent (2) 1:5 with water.

4. Sodium cyanide 10%

5. Sodium nitroprusside, 5%. Prepare fresh.

6. Dilute hydrochloric acid (approx. 2N)

7. Dilute sulphuric acid (approx. 2N) 8. Potassium permanganate solution, 0.3%

9. Ammonium molybdate, 5%. Prepare fresh.

10. Potassium hydroxide solution (approx. 2N)

11. Ammonium oxalate, saturated.

12. Titan yellow, 0.1%

Method

1. Wash the stone with water and dry in incubator. Note the size, appearance and hardness of the stone. Cut the stone to see if layers and nucleus are present. Powder the stone finely.

2. Heat a small amount of the powder in a small crucible or on a foil and observe. (i) Organic crystal such as uric acid or cystine will burn away entirely, leaving a trace of ash.

(ii) Cystine gives a blue flame with a sharp smell.

(iii) Fibrin gives a yellow flame with a smell of burnt feathers.

(iv) Uric acid, ammonium urate and xanthine burn away without flame.

(v) If the stone burns away completely, oxalate phosphate and carbonate are absent.

 (vi) If the stone leaves a residue, proceed for inorganic components from step5.

3. Murexide test:: In a small crucible, add small amount of powder and 2-3 drops of conc. nitric acid. Heat carefully over a flame.

(i) Uric acid or ammonium biurate is present ifred or yellow residue is obtained. When cool, add 2-3 drops of dilute ammonium hydroxide. The colour changes to purple red.

(ii) Xanthine dissolves in nitric acid giving a yellow residue and changes to orange-red on addition of dilute ammonium hydroxide.

4. Cyanide-nitroprusside test for cystine: If a blue flame is seen in Step 2, dissolve a small amount of powder in a few drops of concentrated ammonia. Remove the supernatant, dilute with 2ml water and add 1 ml sodium cyanide. Stand for 5 minutes and add a few drops of sodium nitroprusside solution. A deep magenta colour indicates cystine.

5. If a residue remains in Step 2, inorganic material is present.

 Proceed as follows:

 (i) To small amount of powder, add a few drops of dilute hydrochloric acid.Effervescence indicates carbonates.

(ii) Add 2 ml of dilute sulphuric acid to a small amount of powder. Heat for 1 minute. Cool to 60-70°C and add potassium permanganate solution dropwise. Prompt decolourisation with effervescence indicates oxalate.

 Dissolve a small amount of the powder in a few ml of concentrated nitric acid. Add equal volume of ammonium molybdate solution and heat to boil. A yellow precipitate indicates presence of phosphates.

 Heat a small amount of the powder with 1-2 ml of potassium hydroxide solution. Hold a moist red litmus paper in the vapour. If it turns blue, ammonia is produced which indicates the presence of triple phosphate or ammonium urate.

  
 Add a small amount of the powder to dilute hydrochloric acid and heat to dissolve. To the supernatant add 1 ml of the ammonium oxalate and enough concentrated ammonia till the solution becomes just alkaline. Add acetic acid till the pH is 5.0. A white precipitate of calcium oxalate indicates the presence of calcium.

Filter the precipitate and to the filtrate add a few drops of Titan yellow. Add potassium hydroxide till it becomes strongly alkaline. Red flocculent precipitate of magnesium hydroxide indicates presence of magnesium.