Urine and Urinalysis

All samples should be midstream and collected in a clean sterile container. Suprapubic aspiration or fresh catheter samples are ideal, but not always practical.

Physical examination

Colour The colour of the urine can vary greatly. Normal urine varies from colourless to dark yellow.

Various factors can affect urine colour.

Turbidity Cloudy urine may be due to excess phosphate crystals precipitating in alkaline urine, which is of no significance. It can however also be seen in pyuria secondary to infection, chyluria (usually secondary to filariasis), hyperuricosuria secondary to a diet high in purine-rich foods, lipiduria and hyperoxaluria.

Odour The normal odour is described as urinoid. In concentrated specimens this can be strong but does not imply infection which has a more pungent smell. Alkaline fermentation causes an ammoniacal smell, and patients with diabetic ketoacidosis produce a urine that may have a sweet or fruity odour. Other causes of abnormal odours are cystine decomposition (a sulphuric smell), gastrointestinal-bladder fistulae (a faecal smell), medications (e.g.vitamin B), and diet (e.g. asparagus).

Dipstick Analysis Immerse the dipstick completely in fresh urine and withdraw immediately, drawing the edge along rim of container to remove excess. Hold the dipstick horizontally before reading.

Specific Gravity SG <1.008 is dilute and >1.020 is concentrated.
Increased specific gravity is seen in conditions causing dehydration, glycosuria, renal artery stenosis, heart failure (secondary to decreased blood flow to the kidneys), inappropriate antidiuretic hormone secretion and proteinuria.7,8 Some dipsticks give falsely high readings in the presence of dextran solutions and IV radiopaque dyes, 1 but this varies, so check the manufacturer's leaflet9

Decreased specific gravity is seen in excessive fluid intake, renal failure, pyelonephritis, and central and nephrogenic diabetes insipidus.10 False low readings are associated with alkaline urine (e.g.a high-citrate diet)1.

pH The range is 4.5 to 8, but urine is commonly acidic (i.e 5.5-6.5) due to metabolic activity.
Acidic urine (low pH) may be caused by diet (e.g. acidic fruits such as cranberries).10 Urine pH generally reflects the blood pH but in renal tubular acidosis (RTA) this is not the case.

In type 1 RTA (distal) the urine is acidic but the blood alkaline. in type 2 (proximal) the urine is initially alkaline but becomes more acidic as the disease progresses. Acidic urine may be associated with uric acid calculi.

Alkaline urine (high pH) is seen in the initial stages of type 2 RTA and also with infection with urease-splitting organisms. Alkaline urine may be associated with the formation of stag-horn calculi.13

Haematuria Dipstick testing for haematuria is based on the peroxidase activity of erythrocytes. However, haemoglobin and myoglobin will also catalyse this reaction. False positives are also seen in dehydration and menstruation.

False negatives are seen in patients taking captopril and vitamin C, proteinuria, elevated specific gravity, pH less than 5.1, and baceturia1,14.

Dipstick testing for haematuria is therefore at best a screening tool which needs the support of microscopy to make a definitive diagnosis.

The causes of haematuria can be divided into those occuring at the glomerular level, renal (i.e. non-glomerular) and urological causes. Glomerular haematuria is typically associated with erythrocyte cases, dysmorphic red blood cells and significant proteinuria, although 20% of patients present with haematuria alone.

Renal haematuria is also associated with significant proteinuria, but there are no associated dysmorphic RBCs or erythrocyte casts. Urologic haematuria is distinguished from other etiologies by the absence of proteinuria, dysmorphic RBCs, and erythrocyte casts. Exercise-induced haematuria is a benign, relatively common condition often is associated with long-distance running. Results of repeat urinalysis after 48 to 72 hours should be negative.

For More Information:

Urine Dipstick Analysis

Urine and Urinalysis.mht