Urinalysis

Keywords: Ketones urine

Specimen:

Random urine; should be tested within 4 h of collection.

Method:

Dipstick tests are available for pH, protein, glucose, ketones, bilirubin, blood, urobilinogen, nitrite, leucocyte esterase.

pH: indicator dyes.

Albumin: tetrabromophenol blue.

Glucose: glucose oxidase.

Ketones: nitroprusside. The test detects acetoacetate and acetone, but not ß-hydroxybutyrate.

Bilirubin: diazonium salt coupling.

Blood: pseudoperoxidase.

Urobilinogen: p-dimethylaminobenzaldehyde.

Nitrite: diazonium salt formation and coupling.

Leucocyte esterase: enzyme assay.

Application:

pH: check for successful therapeutic acidification or alkalinisation.

Albumin: suspected nephrotic syndrome, glomerulonephritis, urinary tract inflammation. Urinalysis will not detect 'microalbuminuria'.

See Albumin urine.

Glucose: diabetes mellitus and other causes of hyperglycaemia. The test should not be used to diagnose hyper- or hypo- glycaemia.

Ketones: diabetic ketoacidosis, starvation ketosis.

Bilirubin: differential diagnosis of jaundice.

Blood: inflammation, trauma, or tumour of renal tract, haemoglobinuria, myoglobinuria, coloured urine.

Urobilinogen: the test is not reliable in the assessment of patients with liver disease.

Nitrite: urinary tract infection.

Leucocyte esterase: urinary tract inflammation.

Interpretation:

pH:inability to acidify urine may indicate distal renal tubular acidosis.

Albumin: Albuminuria > 300 mg/L suggests a glomerular protein leak or inflammatory exudate along the urinary tract.

Glucose: positive indicates hyperglycaemia at the time of urine formation, or renal glucosuria.

Hypoglycaemic coma may be present when urine shows glucosuria from earlier hyperglycaemia.

Glucosuria is not a reliable indicator of gestational diabetes and the test should not be used for this purpose.

Absence of glucose with presence of reducing substance (positive Clinitest®) indicates presence of reducing substance other than glucose eg, galactose.

See Reducing substances urine.

Ketones: in a diabetic, positive ketones indicate ketoacidosis. If lactic acidosis is also present, the ketone reaction may be inappropriately weak.

Bilirubin: a negative result in an apparently jaundiced person suggests unconjugated hyperbilirubinaemia (haemolysis, Gilbert syndrome) or carotenaemia.

A positive result is found in hepatocellular or obstructive jaundice.

Blood: a positive test for blood may be due to red cells from inflammation, trauma, or tumour of the renal tract.

Contamination of urine from vaginal bleeding may also be responsible.

If no red cells are seen on microscopy, it indicates haemoglobinuria or myoglobinuria.

A negative test with red urine indicates presence of a coloured compound eg, beetroot, porphyrins.

Urobilinogen: increased in haemolysis. Unreliable as a guide to liver disease.

Nitrite: positive in most bacterial urinary tract infections; negative in urinary tract infections caused by Gram-positive organisms or Pseudomonas spp.

Leucocyte esterase: positive indicates presence of neutrophils.

Reference:

Free HM and Free AH. Urinalysis in Clinical Laboratory Practice. 1975. CRC Press.