Page 474 - Concise Pathology for Exam Preparation ( PDFDrive )

16 Diseases of the Kidney and Lower Urinary Tract 459

Physical Analysis of Urine
Colour

Normal colour of urine is due to three pigments, namely, urochrome, urobilin, uroerythrin.
The following colour changes can be seen in different clinical conditions:
• Pale urine: high fluid intake
• Dark urine: dehydration
• Cloudy urine: presence of mucus, precipitation of phosphates or urates (turbidity disappears
on addition of acetic acid), bacterial growth, sperms and prostatic fluid
• Red urine: presence of haemoglobin, RBCs, myoglobin, porphyrins, beets and menstrual
contamination
• Milky urine: pyuria, lipiduria and chyluria

Odour

• Normal urine has a faint aromatic odour. Bacterial contamination leads to an ammoniacal,
fetid odour.
• Characteristic odour is noted in some conditions, eg, mousy in phenylketonuria, sulphuric
smell in cysteine decomposition, faecal smell in gastrointestinal-bladder fistulae and other
abnormal smells with some medications (vitamin B 6 ); and diet (asparagus).

Volume

• Normal: 1200–1500 mL in 24 h.
• Polyuria: More than 2000 mL of urine in 24 h (seen in excessive fluid intake, diuretic therapy,
chronic kidney disease, diabetes insipidus, mental disorders, DM and primary aldosteronism)
• Nocturia: More than 500 mL of urine with a specific gravity of less than 1.018 at night.
• Oliguria: Less than 500 mL of urine in 24 h (seen in dehydration, acute glomerulonephritis,
shock, toxic nephropathy, obstruction to urinary flow)
• Anuria: Complete suppression of urine formation

Specific Gravity (SG)

• Normal: 1.016–1.022
• Low SG (hyposthenuria): SG less than 1.007 (seen in excessive fluid intake, diuretic
therapy, chronic kidney disease, diabetes insipidus)
• Low fixed SG (isosthenuria): SG fixed at 1.010 (seen in chronic renal failure), as the
concentrating power of kidney is lost due to tubular damage
• Increased SG: SG greater than 1.022 (seen in dehydration, glycosuria, renal artery stenosis,
heart failure due to decreased blood flow to the kidneys, inappropriate antidiuretic hormone
secretion and proteinuria)

Methods of Estimation of Specific Gravity
1. Urinometer
(a) Fill three-fourth of the cylinder of the urinometer with urine (minimum volume
required 15 mL). Gently lower the urinometer in the cylinder and set the urinom-
eter in spinning motion (should be free floating; not touching sides; there should
be no bubbles).
(b) Read bottom of meniscus
(c) Calibrate with:
(i) Temperature—0.001 for each 3°C above or below 20°C
(ii) Protein concentration—0.003 for every 1 g/100 mL protein
Check calibration every day by measurement of specific gravity of distilled
water (which is 1.000).
2. Refractometer: Requires only a few drops of urine. It is used to measure the refractive
index. Refractometers are instruments that can relate density of a solution to specific
gravity. They work on the principle that light passing from a transparent medium of one

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