Urine Dipstick Analysis

• All samples should be midstream and collected in a clean sterile container.
• Immerse the dipstick completely in fresh urine and withdraw immediately, drawing edge along rim of container to remove excess.
• Hold dipstick horizontally before reading.
• Presence of high levels of ascorbic acid may affect readings for glucose and bilirubin.

• Positive test indicates either haematuria, haemoglobinuria or myoglobinuria.
• Dipstick test for presence of haemoglobin with degree of colour change directly related to amount present.
• Can appear as both coloured dots and change in the colour field.
• Free haemoglobin or myoglobin cause field change; intact red blood cells (RBC) are broken down on contact with the reagent pad and release local haemoglobin, producing a dot. These coalesce when >250 RBCs/ml.
• False positive readings are most often due to contamination with menstrual blood. Incidence of false positives can be increased by dehydration which concentrates the number of RBCs produced and exercise.
• Haematuria is defined as >3 RBC/high power field (hpf) of centrifuged sediment under microscope.
• Dipsticks are 90% sensitive but somewhat less specific.
• Prognostic significance of positive test is very controversial, rates ranging from 0.5 - 6% of patients with positive test have been found to have underlying significant pathology.

• Healthy adults normally excrete 80-150mg protein in urine daily.
• Detectible proteinuria may be first sign of renovascular, glomerular or tubulo interstitial renal disease.
• Alternatively may be caused by overflow of abnormal proteins in diseases such as multiple myeloma.
• The dipstick detects presence of protein by increasingly darker shades of green. Minimum detectible protein concentration is 20-30mg/dl.
• False negatives can occur in alkaline or dilute urine or when primary protein is not albumin. More accurate method is to precipitate urinary proteins with 3% sulfosalicylic acid (detects at 15mg/dl and detects other proteins). If urine negative on dipstick but strongly positive with sulfosalicylic acid, suspect multiple myeloma. With positive test use quantitative 24 hour urinary collection and test with protein electrophoresis or immunoassay.

• Transient; occurs commonly especially in children and usually resolves within a few days often associated with fever, exercise or stress. In older patients may be due to congestive heart failure.
• Intermittent; frequently associated with postural changes. Commonly occurs in upright position in young adults and rarely exceeds 1g/day. Resolves spontaneously in about half of patients and not associated with disease. If normal renal function evaluate no further.
• Persistent; usually due to glomerular cause with >2g protein/day of which major component is albumin. Some may also coexist with haematuria.

• Useful screen for diabetes mellitus.
• Urine testing for glucose is also useful in patients who find blood glucose monitoring difficult. Tests for glucose range from reagent strips specific for glucose to reagent tablets which detect all reducing sugars. Tests for ketones by patients are rarely required unless they become unwell.
  Microalbuminuria can be detected with Micral-Test II® or Microbumintest® but this should be followed by confirmation in the laboratory, since false positive results are common.
• Nearly all glucose filtered by the glomeruli is reabsorbed in the proximal tubules and only undetectable amounts appear in urine in healthy patients. Above renal threshold (180mg/dl) glucose will appear in urine. Test relies upon reaction of glucose with glucose oxidase on dipstick to form hydrogen peroxide which causes colour change. This is specific to glucose and no other sugar.

• Occurs in diabetic ketoacidosis, pregnancy and following starvation or rapid weight loss.
• Dipstick test presence of aceoacetic acid at 5-10mg/dl but not acetone or beta-hydroxybutyric acid.

• Urine normally contains no bilirubin and only very little urobilinogen.
• Conjugated bilirubin only appears in urine in presence of liver disease or obstruction of bile duct.

• Leucocyte esterase activity is due to presence of white blood cells in urine.
• Nitrites strongly suggest bacteriuria. They are present because many species of gram-negative bacteria convert nitrates to nitrites.
• Test has variable sensitivity but high specificity. May not be a suitable substitute for microscopic examination.^1,2

Nitrites

There have been many studies evaluating the accuracy of dipsticks tests. Thes are mostly in relation to their role detecting bacteriuria and UTI. The most recent meta-analysis of 26 studies in children, showed wide differences in diagnostic accuracy across studies. This could not be fully explained by differences in age, or by differences in the definition of the criterion standard.³ The lack of an adequate explanation for the heterogeneity of the dipstick accuracy stimulates an ongoing debate.
Overall, the sensitivity of the urine dipstick test for nitrites has been found to be low (45 %- 60% in most situations) with higher levels of specificity (85 %- 98%).⁴ The test for nitrites has its highest accuracy in specific populations such as pregnant women, urology patients and elderly people. The test for nitrites may perform better in asymptomatic patients and in patients who are not on antibiotics.

Leucocyte-esterase

Sensitivity of the urine dipstick test for leucocyte-esterase has been found to be, in general, slightly higher than for the dipstick test for nitrites (48 %-86%), while the specificity was slightly lower (17 %- 93%).⁴ Generally, this results in a lower accuracy, compared to the test for nitrites, lower predictive values of positive test results and similar predictive values of negative test results.
The leucocyte-esterase test has been found to have a much higher accuracy in urology patients. Sensitivity is highest in primary care, but requires further investigations because of the high rates of false positives. In primary care negative results do not exclude the presence of infection.