Urine Dipstick test

Glucose is not normally present in the urine with < 0.1% of glucose normally filtered by the glomerulus appears in urine (< 130 mg/24 hr).
Glycosuria occurs in patients with elevated serum glucose levels (e.g. diabetes mellitus see chapter on hyperglycaemia) or in the presence of a reduced renal threshold and reduced glucose reabsorption in renal tubular disease and pregnancy.
Glycosuria also associated with certain drugs such as cephalosporins, penicillins, nitrofurantoin, methyldopa, tetracycline, lithium, carbamazepine, phenothiazines, steroids and thiazides
- False positive: Hydrogen peroxide or bleach
- False negative: Ascorbic acid (vitamin C) or fruit juices. Some dipsticks are affected by increased specific gravity and ketonuria.

Bilirubin is not present in the urine of normal healthy individuals. The presence of bilirubinuria may be an early indicator of liver disease and occur before the clinical signs of jaundice develop.
Failure of conjugated bilirubin to reach the intestines (e.g. biliary obstruction) will result in bilirubinuria. Note: Only conjugated bilirubin can be excreted as bilirubinuria. A positive test for urine bilirubin confirms conjugated hyperbilirubinaemia. (Reference)
Raised conjugated bilirubinaemia (with bilirubinuria) is associated with hepatocellular disease, cirrhosis, viral and drug induced hepatitis, biliary tract obstruction (e.g. choledocholithiasis), pancreatic causes of obstructive jaundice (e.g. carcinoma of the head of the pancreas) and recurrent idiopathic jaundice of pregnancy
- False positive: Phenothiazines
- False negative: Ascorbic acid (vitamin C), aged sample (conjugated bilirubin hydrolses to unconjugated bilirubin at room temperature), rifampicin and exposure to UV light (converts bilirubin to biliverdin)

Ketones (acetone, acetoacetic acid, beta-hydroxybutyric acid) are the end-point of incomplete fat metabolism. They accumulate in the plasma and are excreted in urine.
Ketonuria is associated with low carbohydrate (high fat/protein) diets, starvation, diabetes, alcoholism, eclampsia and hyperthyroidism.
Ketonuria also associated with overdose of insulin, isoniazid and isopropyl alcohol.
Most urinalysis reagent tests utilise the nitroprusside test which is most sensitive to acetoacetic acid, less sensitive to acetone, and not sensitive to beta-hydroxybutyric acid
- False positive: Heavily pigmented urine. Drugs such as captopril, L-dopa, salicylates, phenothiazines.
- False negative: Negative nitroprusside tests for ketonuria underestimate the presence of ketonemia due to increased beta-hydroxybutyric acid concentrations (Reference)

Determines the presence of whole or lysed white cells in the urine (pyuria) by detecting leucocyte esterase activity.
A positive leucocyte esterase test correlates well with pyuria. However, the diagnosis may be missed in up to 20% of cases if a negative urinalysis dipstick is used to exclude UTI.

False positive: Contaminated specimen, trichomonas vaginalis, drugs or foods that colour the urine red
False negative: Intercurrent or recent antibiotic therapy (especially gentamicin, tetracycline and cephalosporins), glycosuria, proteinuria, high specific gravity. Low bacteria count UTI (especially in women)

Nitrates in the urine are converted to nitrites in the presence of Gram-negative bacteria such as E.coli and Klebsiella.
A positive nitrite test is a surrogate marker of bacteruria.(UTI)
Positive test strongly suggests infection(UTI) but negative test does not exclude it (PPV 95% and NPV 25-70%)
False negative: Drugs or foods that colour the urine red. Certain bacteria such as S. saprophyticus, acinetobacter and most enterococci

The kidneys play an important role in acid-base regulation within the body to maintain a normal urinary pH range between 5.5 – 6.5 but it may vary from as low as 4.5 to as high as 8.0.
The glomerular filtrate of blood plasma is usually acidified by renal tubules and collecting ducts from a pH of 7.4 to about 6 in the final urine.
Control of pH is important in the management of several diseases, including bacteriuria, renal calculi, and drug therapy.

High Urinary pH (Alkali Urine)

Vegetarian diet, low carbohydrate diet or ingestion of citrus fruit (although citrus fruits are acidic – the digestion process leaves an alkali ash)
Systemic alkalosis (metabolic or respiratory)
Renal tubular acidosis (RTA I (distal)), Fanconi syndrome
Urinary tract infections (bacteriuria with urea splitting organisms)
Drugs: Amphotercin B, carbonic anhydrase inhibitors (acetazolamide), NaHCO3, salicylate OD
Stale ammoniacal sample (left standing)

Low Urinary pH (Acidic urine)

Normal daily protein excretion should not exceed 150mg/24 hours or 10mg/100mL. Proteinuria is defined by the production of >150mg/day with nephrotic syndrome producing >3.5g/day
Dipstick urinalysis detects protein with Bromphenol blue indicator dye and is most sensitive to albumin and less sensitive to Bence-Jones protein and globulins. Trace positive results are equivalent to 10 mg/100 ml or about 150 mg/24 hours (the upper limit of normal).

True protein elevation:

Renal: Increased renal tubular secretion,increased glomerular filtration (glomerular disease), nephrotic syndrome, pyelonephritis, glomerulonephritis, malignant hypertension
CVS: Benign HT, CCF, SBE
Functional proteinuria (albuminuria): fever, cold exposure, stress, pregnancy, eclampsia, CHF, shock, severe exercise
Other: Orthostatic proteinuria, electric current injury, hypokalaemia, Cushing syndrome
Drugs: Aminoglycosides, gold, amphotericin, NSAID, sulphonamides, penicillins

False Positive: Concentrated urine (UO<2.5L/day), alkaline urine (pH >7.5), trace residue of bleach, aceazolomide, cephalosporins, NaHCO3
False Negative: Dilute urine (UO >5.0 litres/day) or acidic urine (pH <5)

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