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Urinalysis
Urine pH
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The acidity of urine reflects renal acid excretion and diet. The kidney can acidify urine to about pH 4.5 and it is normally slightly acidic, around 5.5 to 6.5.
Reference interval
| Conventional (pH units) | SI (pH units) | |
|---|---|---|
| Adults | 4.5–8 pH units | 4.5–8 pH units |
Specimen: Fresh random urine · Conventional × 1 = SI
Causes of high values
Alkaline urine: urinary infection with urease-producing bacteria (Proteus), renal tubular acidosis, vegetarian diet, vomiting, alkali therapy, old or contaminated samples.
Causes of low values
Acidic urine: high-protein diet, diabetic ketoacidosis, starvation, diarrhoea, metabolic or respiratory acidosis with normal kidneys, certain drugs. Persistently acidic urine favours uric acid and cystine stones.
Pre-analytical and method notes
The usual range is 4.5 to 8 and the dipstick reads in 0.5 to 1 unit steps. Urine left standing becomes alkaline through bacterial growth and loss of carbon dioxide, so examine fresh samples; pH meters are more accurate than reagent strips. Reference intervals vary by laboratory, method and population; use the interval printed on the report.
References
- McPherson RA, Pincus MR. Henry's Clinical Diagnosis and Management by Laboratory Methods. Elsevier — Tier 3 (textbook)
- Rifai N, Horvath AR, Wittwer CT. Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Elsevier, 6th edition (2018) — Tier 3 (textbook)
- Brenner and Rector's The Kidney. Elsevier, 11th edition (2019) — Tier 3 (textbook)
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