PH

pH of urine

Reflects the kidney's role in maintaining acid-base balance.

Major regulators of acid-base balance

Lungs and kidneys

How do the kidneys regulate acid-base balance?

Secrete hydrogen ions (NH4+, hydrogen phosphate, weak organic acids) and reabsorb bicarbonate.

Normal random urine pH

4.5–8.0

Average urine pH

6.0

Normal fasting urine pH

5.5–6.5

Normal first morning urine pH

5.0–6.0

Lowest normal urine pH

4.5

Highest normal urine pH

8.0

Most common cause of acidic urine

Ketosis

Ketosis causes of acidic urine

Diabetes mellitus, starvation, febrile illness in children

Why does ketosis produce acidic urine?

Increased ammonium ion (NH4+) excretion

Systemic acidosis effect on urine

Intense urine acidity and increased NH4+ excretion

Purpose of acidification therapy

Treat urinary tract infections

Another purpose of acidification therapy

Prevents precipitation of calcium carbonate, calcium phosphate, and magnesium ammonium phosphate

Pulmonary emphysema urine pH

Acidic

Dehydration urine pH

Acidic

Diarrhea urine pH

Acidic

Acid-producing bacteria causing acidic urine

Escherichia coli

High-protein diet effect on urine

Produces acidic urine

Why does a high-protein diet acidify urine?

Meat metabolism produces acids.

Cranberry juice effect on urine

Produces acidic urine

Gout urine pH

Acidic

Normal cause of alkaline urine after eating

Postprandial alkaline tide

Postprandial alkaline tide

Normal alkaline urine shortly after meals

Systemic alkalosis causes

Severe vomiting, hyperventilation, excess alkali ingestion

Renal tubular acidosis urine pH

Alkaline due to impaired tubular acidification

Urease-producing bacteria

Proteus and Pseudomonas

How do urease-producing bacteria alkalinize urine?

Convert urea into ammonia.

Vegetarian diet effect on urine

Produces alkaline urine due to bicarbonate formation

Old or stale urine specimen

Suggests bacterial overgrowth and alkaline urine

Acute and chronic renal failure urine pH

May produce alkaline urine

Diuretics effect on urine

May cause alkaline urine

Alkalinization therapy drugs

Sodium bicarbonate, potassium citrate, acetazolamide

Purpose of alkalinization therapy

Prevent crystallization of uric acid, oxalate, cystine, sulfonamides, and streptomycin

Another use of alkalinization therapy

Treatment of salicylate poisoning

Clinical significance of urine pH

Helps determine systemic acid-base disorders

Urine pH in respiratory/metabolic acidosis

Acidic

Urine pH in respiratory/metabolic alkalosis

Alkaline

Why maintain a specific urine pH?

Prevent renal calculi formation

Another use of urine pH

Helps identify urinary crystals

Urine pH in UTI treatment

Maintain acidic urine for infections caused by urea-splitting organisms

Why alkalinize urine in salicylate poisoning?

Increases salicylate excretion

Urine pH helps assess

Patient dietary intake

Freshly voided urine maximum pH

pH does not normally reach 9

pH reagent strip principle

Double-indicator system

Indicators used in pH reagent strip

Methyl red and bromothymol blue

Methyl red color change

Red-orange to yellow

Bromothymol blue color change

Green to blue

Cause of falsely low pH reading on reagent strip

Run-over from the protein pad

Bacterial interference in urine pH

Certain bacteria produce a marked alkaline shift