Mohamad reza tohidi
Kermanshah University of Medical Sciences
The kidneys and lungs normally work in concert to maintain acid-base
The lung excretes carbon dioxide
the renal contribution is that of reclaiming and generating bicarbonate and
secreting ammonium ions
The proximal renal tubule is responsible for the bulk of the bicarbonate
reabsorption/generation, and the distal tubule provides the remaining
The tubular cells exchange hydrogen ions for sodium of the glomerular
The metabolic activity of the body produces nonvolatile acids, principally sulfuric,
phosphoric, and hydrochloric acids, but also small amounts of pyruvic, lactic, and citric
acids and ketone bodies.
These are excreted by the glomerulus as salts (sodium, potassium, calcium, and
ammonium salts) and, together with ammonia produced by the renal tubules, can then
go on to trap secreted hydrogen ions for elimination in the urine
urine pH, a reflection of acid–base balance
In healthy individuals, urine pH may vary from 4.5to 8.
It varies with food intake (lower pH with high protein diet).
Fasting produces low values, and the highest pH measurements are seen following
Measurement of urine pH and acidity must always be made on freshly voided
Measured by pH meter with a glass electrode (more accurate) or reagent strips(is
measurement with a pH meter may be indicated in some clinical circumstances, such
as the diagnosis and treatment of patients with disturbances of acid-base
balance or monitoring urine alkalinization in patients receiving high-dose
methotrexate therapy or undergoing treatment for nephrolithiasis
Dipsticks can read pH 5–9.They are not accurate when pH <5.5 or >7.5.
urine pH, a reflection of acid–base balance
• Early morning pH <5.5 is an indicator of good acidification
• pH >7 may suggest defective acidification in absence of infection and
pH values are low where acidemia is present
except for where this is secondary to renal tubular acidosis
Urinary pH is important in diagnosing :
renal tubular acidosis and monitoring
in the treatment or prevention of urinary stones
Therapeutic urinary alkalinization may be indicated in cystine and urate
poisonings (salicylates, methotrexate, and barbiturates)
Alkaline urine in a patient with urinary tract infection suggests presence of
a urea-splitting organism like Proteus
a diet high in meat protein and with some fruits such as cranberries
SOME CONDITIONES WITH LOW PH URINE :
Diabetic ketoacidosis(metabolic acidosis) large quantities of hydrogen ions are
excreted, much as ammonium ion
During the mild respiratory acidosis of sleep, a more acid urine may be formed
In acid-base disturbances, the pH of the urine reflects
attempts at compensation by the kidneys.
Patients with metabolic or respiratory acidosis should
produce acid urine with increased titratable acidity and
ammonium ion concentration.
Urinary pH generally reflects the serum pH, except in
patients with renal tubular acidosis
an increased incidence of nephrolithiasis in low PH urine
Therapeutic acidification of the urine by various pharmacologic agents,
including ammonium chloride, methionine, and methenamine mandelate,
is used in the treatment of some calculi.
This would include phosphate and calcium carbonate stones, which tend to
develop in alkaline urine.
In potassium depletion, such as in hypokalemic alkalosis of prolonged
vomiting, or with prolonged use of diuretics, paradoxical aciduria with
slightly acid urine may occur in the presence of a metabolic alkalosis.
Alkaline urine may be induced by a diet high in certain fruits and
vegetables, (especially citrus fruits )
The urine tends to become less acid following a meal (the so-called
alkaline tide). And tends to become more acid during fasting .
In metabolic alkalosis:
an alkaline urine with higher levels of urinary bicarbonate is produced, and
ammonia production is decreased.
In respiratory alkalosis:
an alkaline urine is produced that is associated with increased excretion of
Urine PH in RTA
The inability to acidify urine to a pH of less than 5.5 despite an overnight fast and
administration of an acid load is the hallmark of RTA.
In type I (distal) RTA :
the serum is acidic but the urine is alkaline, secondary to an inability to secrete protons
into the urine and inability to form of ammonia and urine PH remain >5.5 despite sever
In Type II (proximal) RTA :
is characterized by an inability to reabsorb bicarbonate(bicarbonate wasting occurs).
This situation initially results in alkaline urine, but as the filtered load of bicarbonate
decreases, the urine becomes more acidic and as distal acidification is intact urine PH
may reduced to <5.5 .
Therapeutic alkalization of urine
Determination of urinary pH is useful in the diagnosis and management of
UTIs and calculi.
Sodium bicarbonate, potassium citrate, and acetazolamide may be used to
induce alkaline urine in the treatment of some calculi, particularly those
composed of uric acid, cystine, or calcium oxalate.
These agents may also be used in some urinary tract infections (the
antibiotics neomycin, kanamycin, and streptomycin are more active in
and in the treatment of salicylate poisoning.
In children, urine pH are associated with certain causative
uropathogens, and less acidic urine is particularly associated with
P. mirabilis or P. aeruginosa infections.
the urine pH is also a predisposing factor of UTI in children.
Alkaline urine in a patient with a UTI suggests the presence of a
urea-splitting organism, which may be associated with
magnesium-ammonium phosphate crystals and can form