Urine pH and Its Significance

Sample

1. The test sample is urine.
2. A fresh urine sample is preferred.

Indications

1. pH tells the systemic acid-base disorder:
   1. Is it metabolic?
   2. Or Respiratory.
   3. Renal tubular acidosis.
2. pH is used to identify the type of crystals.
3. pH is important to manage diseases, bacteriuria, renal calculi, and drug therapy.

Pathophysiology

1. The lungs and the kidneys are the major regulators of the acid-base content in the body.
   1. Lungs and the kidneys maintain the pH and acid-base balance by secretion of H+ ions in ammonium ions, hydrogen phosphate, weak organic acid, and reabsorption of bicarbonate from the filtrate in the convoluted tubules.
2. A healthy individual will produce morning urine as acidic with a pH of 5.0  to 6.0.
   1. Alkaline urine may be found after the meals (alkaline tide).
   2. The random pH ranges from 4.5 to 8.0.
3. pH measures the free hydrogen (H⁺) ions concentration in the urine.
4. Urine pH when it is :
   1. 7.0 = neutral
   2. < 7.0 = acidic.
   3. > 7.0 = alkaline.
5. Urine pH indicates renal tubules ability:
   1. To maintain normal H⁺ concentration in the plasma.
   2. To maintain the extracellular H+ concentration.
6. Mechanism of the control of pH:
7. The kidneys are the major regulator of the acid-base content in the body.
8. Renal distal tubules are the most active site for homeostasis for:
   1. Plasma electrolyte balance.
   2. Plasma acid-base balance.
9. In the distal tubules, there is a combination of secretion and reabsorption of:
   1. Na⁺
   2. K ⁺
   3. H⁺
10. In the distal tubules, there is an exchange of H⁺ for Na^+.
    

    Urine control of pH

11. Kidneys have the main function of producing alkaline or acidic urine and maintain constant body pH.
12. Kidneys maintain acid-base by absorption of Na and excretion of H and ammonia.
13. Significance of urine pH:
    1. In respiratory or metabolic acidosis, when there is no renal dysfunction, then urine will be acidic.
    2. While in the case of respiratory or metabolic alkalosis, when there is no renal dysfunction, urine will be alkaline.

Hydrogen ions secretion and reabsorption in the kidney shown in the table:

Hydrogen ions	Prox. tubule	Loop of Henle	Collecting ducts
Secretion	+	+	+
Reabsorption	–	–	+

Normal

Source 2

• Normal pH varies from 4.6 to  8.0  (average 6.0).

Lab measurement of urine pH:

1. Test strips impregnated with the indicator.
   1. Methyl red in urine pH below 4.2 is red.
      1. pH above 6.2 is yellow.
   2. Bromthymol blue is yellow at a pH value below 6.0.
      1. Blue at the value above 7.6.
   3. In between the pH, there are shades of orange and green.
      1. Read after 60 seconds and compare the colors with the given color chart.
      2. Whereat pH 5 is orange and at pH 8.5 is blue.
2. pH electrodes are more accurate.

High pH > 7.0 urine Indicates Alkaline urine, maybe due to:

1. Gastric suction
2. Renal Failure
3. Vomiting (metabolic acidosis)
4. Respiratory alkalosis.
5. Hyperventilation.
6. Potassium depletion.
7. A bacterial infection like Proteus and Pseudomonas.

Low pH < 7.0 urine indicates Acidic urine, maybe due to:

1. Metabolic acidosis.
2. A bacterial infection like E.coli.
3. Renal tuberculosis.
4. Fever.
5. Diabetic ketosis.
6. Diarrhea.
7. Starvation.
8. Uremia.

Causes of acid and alkaline urine:

Alkaline urine	Acidic urine
Vomiting	Diabetes mellitus
Hyperventilation	Starvation
Vegetarian diet	Diarrhea
Old specimen	Dehydration
Renal tubular acidosis	High protein diet
Urease-producing bacteria	Emphysema
	Acid-producing bacteria (E.coli)
	Cranberry juice
	Medicines

pH urine role in renal calculi:

1. The renal stone formation depends upon urine pH.
   1. Calcium phosphate, calcium carbonate, and magnesium phosphate stones form in alkaline pH,  so keep the urine acidic to prevent their formation.
   2. Uric acid, calcium oxalate, and cystine form in acidic urine; to prevent their formation, keep the urine pH alkaline.

pH urine role in drug therapy:

1. Neomycin, kanamycin, and streptomycin are effective in alkaline urine.
2. Salicylate intoxication keeps the urine pH alkaline.
3. Sulfa therapy forms crystals, and these can be prevented by keeping urine pH alkaline.

pH urine role in diseases:

1. keep urine pH acidic during :
   1. The treatment of urinary tract infection.
   2. In persistent bacteriuria.
   3. In renal calculi, which develop in alkaline urine.

Diet effect on the urine pH:

1. Vegetarian diet, citrus fruits keep urine alkaline.
2. Diet rich in protein (meat) keeps urine acidic.
3. Cranberry juice keeps urine acidic, and some believe it is a remedy for UTI.

Summary of the significance of the urine pH:

1. For assessment of metabolic alkalosis and acidosis.
2. For assessment of respiratory alkalosis and acidosis.
3. To find an unsatisfactory urine specimen.
4. Role in the formation of renal calculi.
5. Role of pH in the differentiation of the crystals in the urine.
6. pH importance in the treatment of urinary tract infection.
7. Role of pH in the renal tubular acidosis.
   

   Characteristics	Etiology	Mechanism
   Acidic urine
   Systemic acidosis	Respiratory acidosis Metabolic acidosis	It is acidic urine Increased ammonium excretion
   Ketosis	Seen in: Diabetes Febrile conditions in children Starvation
   Acidification treatment		Used for treating the urinary infection To prevent precipitation of : CaCO3 PO4 Magnesium Ammonium PO4
   Alkaline urine
   After the food	Postprandial	There is a spike after the food called alkaline tide.
   Vegetarian food	Meat produce acid urine	Produce alkaline urine
   Urinary tract infection	Proteus Pseudomonas	These split urea to CO2 and NH3
   Drugs to make alkaline urine		Prevents crystalization of: Uric acid Oxalate Cystine Streptomycin Sulfonamides
   State of alkalosis	It is seen in: Hyperventilation Vomiting (severe) Increased intake alkali
   Renal tubular acidosis	There is impaired tubular acidification	There is high urine pH Low serum HCO3

Normal urine picture:

Physical features	Chemical features	Microscopic findings
Color = Pale yellow or amber Appearance = Clear to slightly hazy pH = 4.5 to 8.0 Specific gravity = 1.015 to 1.025	Blood = Negative Glucose = Negative Ketones= Negative Protein = Negative Bilirubin = Negative Urobilinogen = Negative (±) Leucocyte esterase = Negative Nitrite for bacteria = Negative	RBCs = Rare or Negative WBC = Rare or Negative Epithelial cells = Few Cast = Negative (Occasional hyaline) Crystal = Negative (Depends upon the pH of the urine) Bacteria = Negative

 

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