Page 475 - Concise Pathology for Exam Preparation ( PDFDrive )

460 SECTION II Diseases of Organ Systems

density to a medium of another density will change its velocity and therefore the
direction in which the beam of light is moving.
3. An indirect colorimetric method for estimating specific gravity is available on reagent
strips (‘urine dipsticks’): This method uses a pad that contains a complex, pretreated
electrolyte that undergoes a pH change based on the ionic concentration of the urine.
This change results in a change of colour of the pad. This estimate of specific gravity is
rapid, simple and requires no special equipment.

pH
• pH is the ability of kidneys to maintain normal hydrogen ion concentration in plasma
and extracellular fluid. Metabolic activity produces nonvolatile acids, eg, sulphuric acid,
phosphoric acid, hydrochloric acid, pyruvic acid, lactic acid, citric acid and ketones.
These are excreted and bicarbonates reabsorbed.
• Normal pH: 4.6–8
• Measured by reagent strips (recommendations: protect the strips from moisture and
heat, store in a cool dry area, do not refrigerate, check for discoloration and check
manufacturer’s directions).

Chemical Analysis of Urine
Chemical examination of urine includes testing for proteins, glucose, ketones, bile
derivatives and blood. Most common abnormalities detected on chemical examina-
tion of urine are
• Glycosuria: Causes include DM, renal glycosuria, pregnancy, alimentary glycosuria,
intravenous infusion of glucose and increased intracranial tension.
• Proteinuria: Kidney diseases (like nephritic syndrome, nephrotic syndrome, tubercu-
lous nephritis, renal cell carcinoma and renal vein thrombosis), muscular exertion, high
fever, heavy metal poisoning and orthostatic albuminuria) can lead to proteinuria.
• Ketonuria: Metabolic abnormalities such as diabetes, glycogen storage diseases, starva-
tion, fasting, high protein, or low carbohydrate diets, prolonged vomiting and hyper-
metabolic states such as fever, pregnancy, or lactation are common causes of ketonuria.
In nondiabetic persons, ketonuria may occur during acute illness or severe stress.

Microscopic Analysis of Urine

• Centrifuge 10/12/15 mL of urine at 450 g for 5 min
• Remove supernatant leaving behind a few drops
• Mix sediment with a drop or two of the supernatant and resuspend
• Smear and examine

RBCs
• Normal: 0–2 cells/HPF or 3–12 cells/µL.
• Appear as faint, colourless circles/shadow cells (due to dissolution of haemoglobin).
• Hypertonic urine shows crenation of RBCs (may be confused with yeast cells but yeast cells
show budding. Also, on adding a few drops of acetic acid, RBCs lyse, but yeast cells do not).
• Distorted RBCs are called dysmorphic erythrocytes (when more than 20% RBCs appear
distorted; the RBCs are regarded as renal in origin).
• Causes of hematuria include:
1. Lesions of the urinary tract
• Kidney: Polycystic kidney, hereditary nephritis, tuberculosis, acute nephritic
syndrome, renal tumours (RCC and Wilms tumour), infarction, pyelonephritis,
IgA nephropathy and trauma
• Ureter: Ureteric calculi, papilloma or carcinoma
• Urinary bladder: Rupture, cystitis, tuberculosis, transitional cell carcinoma (TCC),
calculi and Schistosoma haematobium infection
• Prostate: Prostatitis, nodular hyperplasia prostate (NHP) and carcinoma prostate
• Urethra: Rupture, urethritis, stricture, calculus and TCC

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