• Urinary pH changes rapidly when in contact with air; therefore, prompt testing is essential
As a general rule, urinary pH reflects serum pH, but there is an important exception.
• In renal tubular acidosis (RTA), the urine will often remain alkaline in spite of the presence of acidic urine, due to urinary bicarbonate loss
• In severe type II RTA (proximal) the urine may occasionally become acidic, but will always remain alkaline even with severe type I RTA (distal)
Additionally, alkaline urine (pH over 7.5) suggests infection by a urea-splitting organism such as Proteus. Vegetarians commonly have alkaline urine due to low acid ingestion. Uric acid and cystine stones form in acidic urine (pH less than 5.5).
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