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Ward

Investigations

URINE TESTS INTERPRETATION

 

1. URINE COLOUR
•    Straw coloured: normal
•    Colourless: diabetes insipidus, diuretics, excessive fluid intake
•    Dark: porphyria, malignant melanoma
•    Cloudy: UTI, blood, mucus
•    Pink: blood, myoglobin, beetroot
•    Orange: rifampicin, bile pigments
•    Brown: myoglobin, melanin, iron
•    Green: methylene blue, urobilinogen

 

2. DIPSTICK ANALYSIS
Leucocytes: UTI (used together with nitrites to diagnose a UTI)

Nitrites: bacteriuria (very specific for a UTI), contaminated sample. A negative test is high likely to exclude a UTI

Glucose: absence in health. Appears once urinary threshold exceeded (approx 10mmol serum glucose). Therefore won’t show impaired glucose tolerance. Causes- diabetes mellitus, pregnancy, pancreatitis

Ketones: breakdown of fatty acids. Diabetic ketoacidosis, starvation, alcohol intoxication, dehydration

Protein: kidney damage or disease, standing upright for prolonged periods, exercise, fever, pregnancy. Doesn’t show microalbuminaemia (earliest sign of renal disease). Doesn’t show Bence-Jones protein

Urobilinogen: increased red blood cell breakdown- not a sensitive test for altered serum billirubin

pH: only a very rough value of blood pH. Normal pH varies between 4.5 and 8.0 depending on diet. In a patient with a UTI, alkaline urine indicates infection with a urea- splitting organism such as proteus. Acidic urine predisposes to formation of uric acid renal stones eg secondary to bicarbonate loss from an ileostomy

Specific gravity: not accurate. Varies with the patient's hydration and falls with age as kidney looses its concentrating ability

Haemoglobin: blood may arise from anywhere along the renal tract. Renal causes include glomerulonephritis, polycystic kidney and neoplasia. Non- renal causes include UTI, calculi and hypertension. It does not distinguish from erythrocyturia (contamination with fresh menstrual blood) and myoglobin

 

3. CULTURE AND SENSITIVITY
•    Differentiates contamination of urine sample by organisms outside the bladder from true infection
•    Low counts: early infection in women or true infection in men (as contamination uncommon in men)

 

4. MICROSCOPY
Urine is spun in a centrifuge so sediment settles out, spread on a slide and examined under a microscope

Indications: UTI, glomerulonephritis, acute interstitial nephritis (eosinophils), renal failure, haematuria on dipstick, suspected malignancy. Use an early morning MSU specimen

Red cells: due to damage to RBCs as they travel through glomeruli you can differentiate often between glomerular (renal) and infrarenal bleeding

Leucocytes: high polymorphs suggestive of UTI but can occur in glomerulonephritis

Other cells: malignant cells, spermatozoa

 

Casts
Cylindrical bodies of cells or protein which form in the distal tubule and collecting duct
•    Hyaline casts: present in normal urine but increase in dehydration and proteinuria
•    Cellular casts: red cell casts indicate paranchymal renal disease especially glomerulonephritis. White cell casts strongly suggestive of acute pylonephritis
•    Granular casts: formed from cell debris and are seen in a wide variety of renal diseases

 

Crystals
•    Presence may indicate kidney stones or a problem with metabolism
•    Need a freshly voided sample as affected by storage and temperature changes
•    Calcium oxalate stones in hypercalciuria. Presence of a single crystal of cysteine is diagnostic of cysteinuria as cysteine is not a constituent of urine

 

 

Author: Johno Breeze
Last updated: 15/02/15