Kidney and Urinalysis

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Kidney and Urinalysis

• Prepared by Sr. Siti Norhaiza Hadzir

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Functions of the kidney

• Elimination of excess body water
• Elimination of waste products of metabolism e.g
  urea creatinine
• Elimination of foreign substances e.g drugs
• Retention of substances necessary for normal body
  function e.g protein, amino acids glucose
• Regulation of electrolytes balance osmotic
  pressure of the body fluids.

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The Nephron

• The functional unit of the kidney.
• Consists of renal corpuscle (glomerulus) renal
  tubule.
• Structure of glomerulus
• Structure of tubule

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Kidney blood supply

• Renal artery from aorta ? afferent arterioles ?
  efferent arterioles ? renal vein ? heart

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Glomerular Filtration Rate

• Normally this amounts to about 130mL per minute
  (180 liters per 24 hours).

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Renal Function Test

• Falls into 2 major group

1. Detect the presence of disease- not give
   indication as to the degree of functional
   impairment e.g proteinuria, cast, hematuria, WBC
2. Evaluate the degree of impairment e.g BUN,
   creatinine

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Test of Urinary tract involvement

• Proteinuria

• Healthy glomerular permeable membrane passes
  only substances with MW of less than 70 000.
• Excess small proteins are reabsorbed completely
  by proximal tubule
• Albumin is very close to cut off value (70000MW)
  can get access to the urine in glomerular
  disease.
• Proteinuria are classified into 3
• Pre-renal- The glomerular membrane damage and
  tubular reabsorption inefficiency e.g Bence Jones
  protein in multiple myeloma.
• Renal- renal parenchyma disease e.g amyloidosis.
• Postrenal- Urinary tract problem e.g inflammation
  

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Figure 1 Normal urine is compared with
proteinuria sample. Note increase in turbidity in
proteinuria sample
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Cast

• Cast are precipitates of protein formed in the
  distal convoluted and collecting tubules of the
  kidney, where conditions of filtrate flow and pH
  are optimal for protein precipitation.
• Normal condition-hyaline cast in small number
• Large number indicates active renal disease.

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Nature of cast

• It is a muco-protein formed normally by the
  tubule it is not formed in plasma.
• It is long, rod like, flexible molecule.
• As the glomerular filtrate travels down the
  nephron tubule, the concentrations of salts H
  ?.
• At pH about 4.5, albumin and myoglobin change
  from negatively to positively charge molecules,
  the muco-protein is still negatively charge.
• Opposite electric charge leads to precipitation
  and the formation of casts.

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Hematuria hemoglobinuria

• Presence indicate bleeding within the urinary
  tract.
• In acute glomerulonephritis there is hemorrhage
  from the glomeruli, Hb is convreted to hematin
  and methemoglobin.
• These factors combine to give the smoky red
  brown urine characteristic of the disease.

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Figure 2 The presence of blood in the urine
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White Blood Cells

• An increased number of white blood cells in a
  correctly collected specimen indicates
  inflammation in the urinary tract.

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Test for Degree of Renal Impairment

• Test based on water elimination and reabsorption
• Blood Urea Nitrogen (BUN)
• Creatinine
• BUN Creatinine

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Test based on water elimination and reabsorption

• Normally, conservation of water is reflected by
  concentrated urine with a high specific gravity
• Excretion of an excess of water is illustrated by
  urine of low specific gravity

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Impaired concentrating power

• Tubular damage e.g chronic glomerulonephritis,
  polycystic disease
• Severe potassium depletion
• Hypercalcemia e.g due to vitamin D intoxication,
  hyperPTH
• Inborn defects of tubular function
• Diabetes insipidus

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Non-protein nitrogen in blood

• It is heterogenous collection of substances
  including urea, creatinine, uric acid,
  nucleotides, glutathione.
• Estimation of NPN was replaced by determination
  of urea and creatinine, more specific indicators
  of renal condition, easily automated.

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Blood Urea/BUN

• Urea is the major excretion product of protein
  catabolism.
• After elaboration, urea is passed to the blood
  and is excreted through the glomeruli and partly
  reabsorbed in the tubules.

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Causes of ? BUN

• Pre-renal Circulation in the kidney is less
  efficient e.g CCF
• Renal Renal parenchyma damage, phylonephritis
• Post-renal Obstruction to the urinary tract
• Presence of high level of urea is called uremia.
• Very high level of urea leads to azotemia with
  kidney failure.

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Creatinine

• Nitrogenous substances found in muscle.
• Since creatinine is derived entirely from
  endogenous metabolism (not form dietary protein)
  and is not reabsorbed by the renal tubules, its
  blood level is a reliable index to renal
  function.

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BUN/creatinine ratio

• Normal ratio is 101.
• Ratio more than 101 occur in
• Ration less than 101 occur in

• Excessive turnover of protein (hemorrhage, burns
  and infection)
• Reduced glomerular perfusion

• Repeated dialysis
• Severe vomiting or diarrhea
• Liver failure

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Routine urinalysis

• The procedure

• Urine collection and storage
• Macroscopic examination
• - Color
• - turbidity and clarity (smoky. milky,
  cloudy)
• - smell
• - SG and osmolality

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Color Possible cause
Straw to amber Normal
Orange Concentrated urine
Greenish orange bilirubin
Smoky Red blood cells
Brown to black on standing Melanin or homogentisic acid
Almost colorless Dilute urine
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Urine container
Centrifuge tube
Pipetting the supernatant
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The procedure cont

• Urine processing

• Centrifuge
• Separate debris and supernatant
• Microscopic examination cells (epithelium, RBC,
  
• WBC, cast, mucus tread, ova and parasites,
• crystals
• Biochemical analysis (pH, protein, glucose,
  ketones, bilirubin, blood, nitrite, urobinogen,
  ascorbic acid)

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Urine dipstick