Specific gravity
- Indirect measure of the concentration of urinary solutes – false negatives and positives
- Ratio compared to water – SG 1.000
- Urine usually around 1.010
- May indicate hydration status, renal failure, diabetes insipidus, SIADH
- Also increases with glucose, protein
pH
- Measures hydrogen ion concentration (acidity)
- Must use fresh sample – urine becomes increasingly alkaline on standing especially with UTI
- Usual range 4.5-8.0
- Changes with diet – low (acidic) with fruits and high protein, high (alkaline) with low carb, vegetarian
- Low in starvation (protein metabolism)
- May reflect blood acid base balance
Leukocyte esterase
- Chemical measure of an enzyme present in white cells
- Normally negative
- Indirectly detects white cells in the urine (pyuria)
- Indicates urinary tract infection or contamination (eg vaginal thrush)
Nitrites
- Normally negative
- Nitrites are formed by the breakdown on urinary nitrates, usually by bacteria especially E.coli, Staphylococcus and Klebsiella which are common causes of UTI
Protein
Measures albumin in the urine
- Normal is negative (none)
- Rises in kidney disease, injury to urinary tract, inflammation, infection, malignancy, multiple myeloma, pre-eclampsia
- Trace is normal in up to 10% of children
- Should be quantified by lab test – 24hr microalbuninuria or albumin:creatinine ratio
Glucose
Normal is negative (none) - Glucose is actively reabsorbed by the kidney
Glycosuria indicates:
- Increased blood glucose – diabetes mellitus, steroids
- Reduced renal threshold – pregnancy, some medications
- Needs to be followed up with BSL
Ketones
Normal is negative (none)
- Increase with fat metabolism
Ketonuria may indicate:
- Diabetes (DKA), alcoholism, eclampsia, starvation or weight loss, pregnancy
Urobilinogen
- Produced from bile in the bowel
- Some is reabsorbed in the colon and a small amount (<1%) is passed by kidneys into the urine
- Raised levels occur with haemolysis (including malaria), hepatitis, cirrhosis
- High levels of bilirubin and absent urobilinogen indicates blockage of bile duct
Bilirubin
Only conjugated bilirubin is water soluble
- :In pre-hepatic jaundice (haemolysis) the bilirubin is unconjugated and does not pass into the urine
Conjugated bilirubin usually passes into the gut via the bile duct but some is carried in the bloodstream to the kidneys
- Increased levels seen in liver disease and bile duct obstruction – cholelithiasis, pancreatic obstruction
Blood
Normal is negative (none). Microscopic vs macroscopic.
Causes of haematuria:
- Kidney Disease – erythrocytes leak through the glomeruli
- Renal Tract Bleeding - trauma, infection, renal calculi, malignancy, catheterisation
- Contamination from vagina esp menstruation
- False positive - strenuous exercise (myoglobinuria)
- Should be quantified by lab microscopy – also can differentiate between renal and non renal RBC’s
False results
- Urine discolouration – drugs, haemoglobin, myoglobin, bilirubin
- Delay in testing – changes pH, becomes more alkaline
- Refrigerated sample – false negative glucose
- Expired strips
Urine microscopy
Lab Test
Urine is centrifuged and sediment examined under microscope. Looking for:
- Cells
- Bacteria
- Crystals
- Casts
Abnormal findings would include more than 0-2 red blood cells, more than 0-2 white blood cells, crystals, casts , renal tubular cells or bacteria. (Bacteria can be present if there was contamination at the time of collection).
Epithelial cells indicate contamination
Urine culture and sensitivity
Urine is plated out in lab to determine what organisms are present and which antibiotics they are sensitive to
Multiple different organisms usually indicate contamination
Beta-HCG
Measures human chorionic gonadotropin (hCG) (hormone produced by the developing placenta shortly after the embryo attaches to the uterine lining)
- Reliably detectable around 14 days after conception or on the first day of a missed period
Urine chlamydia and gonorrhoea
- Collect a first pass urine - first part of stream, preferably but not necessarily first urine of day
- Works by looking for bacterial DNA using a process called LCR (ligase chain reaction) or other DNA amplification techniques
- These types of testing are sensitive to even very small amounts of bacterial DNA and do not require a live bacterial sample – good screening test
- Gold standard is still culture from cervical or urethral swab
- Can also be used for sensitivities
