Kidney Function and Hormones Quiz

Renal Function and Integrity Tests

• Kidney functions include control of body fluid balance (volume and composition), maintenance of water, electrolyte and acid-base balance, conservation of nutrients, regulation of blood pressure, and production of hormones like erythropoietin and calcitriol (active Vitamin D) and renin.

Learning Outcomes

• Outline the major kidney functions.
• List tests recommended for assessing renal function.
• Explain the purpose, interpretation, and limitations of various renal function tests.
• Interpret azotemia in a clinical scenario.
• List other laboratory abnormalities in kidney disease and explain pathogenesis.
• Interpret urinalysis (including USG, dipstick, and sediment).

Nephron

• The nephron is the structural and functional unit of the kidney, consisting of glomerulus, Bowman's capsule, tubules, collecting duct, and blood vessels.

Renal Function Tests

• Blood tests: Biochemistry (nitrogenous wastes like urea and creatinine, electrolytes and minerals like Na+, Cl, K+, Ca2+, PO4), Haematology, and Blood gas analysis.
• Urinalysis: USG, dipstick, sediment, UPCR (may be done).

Glomerular Filtration Rate (GFR)

• GFR measures the rate of fluid movement from plasma to glomerular filtrate.
• Methods:
  • Inulin clearance (direct measurement)
  • Urea and creatinine (indirect estimations)

Urea - Physiology

• Urea is synthesized in hepatocytes via the urea cycle, eliminating excess NH4+ formed in tissues.
• Urea passes freely across the glomerular filtration barrier.
• Half is reabsorbed in the proximal and collecting tubules, and the rest is excreted; a small part in feces.

Urea - Pathology

• Decreased excretion: Prerenal, renal, postrenal azotemia, intestinal hemorrhage, increased proteolysis, and increased protein intake.
• Decreased synthesis: Liver insufficiency, decreased protein intake, urea cycle enzyme deficiencies, any cause of polyuria.
• Increased excretion: increased protein intake, high muscle mass.

Creatinine - Physiology

• Creatinine is constantly produced from creatine degradation in muscles.
• Passes freely across the glomerular filtration barrier.
• Not reabsorbed, but might be excreted by proximal tubules.
• Excretion in feces (?).

Creatinine - Pathology

• Decreased excretion: Prerenal, renal, postrenal conditions, high muscle mass, increased protein intake.
• Decreased production: Reduced muscle mass.

Azotemia

• An increase in nonprotein nitrogenous compounds in the blood, detected as increased serum urea and/or creatinine concentration.
  • Prerenal: Reduced renal blood flow.
  • Renal: Kidney disease.
  • Postrenal: Obstruction of urinary tract.

Prerenal Azotemia

• Characterized by reduced renal blood flow, hypovolemia, decreased cardiac output, and signs of dehydration.
• Urine tends to be concentrated (USG > 1.030 in dogs, USG > 1.035 in cats)

Renal Azotemia

• Caused by kidney disease.
• Loss of approximately 75% of nephron functional capacity, insufficient GFR to produce azotemia.
• Urine may be inadequately concentrated (USG <1.030 in dogs, USG < 1.035 in cats).

Postrenal Azotemia

• Caused by obstruction of the urinary tract at a point distal to the kidney.

Symmetric Dimethylarginine (SDMA)

• A methylated amino acid, produced during protein turnover, excreted almost entirely by kidneys.
• A linear relationship with GFR (unlike creatinine).
• Useful for early detection of chronic kidney disease (CKD)

Abnormal Biochemistry in Azotaemic Animals

• Notable examples include potassium, phosphorus, calcium, pH, lipase, and amylase.

Phosphorus and Calcium

• Hyperphosphotemia: Reduced plasma clearance of phosphorus.
• Total Calcium may be decreased, normal, or increased.
• Reduced renal formation of 1,25-dihydroxycholecalciferol
• Increase in the amount of calcium bound to non-protein anions.

Potassium

• Increased: Reduced renal excretion (anuria, oliguria, terminal CKD), redistribution between intracellular and extracellular compartments (inorganic acidaemia).
• Decreased: Increased urinary loss (polyuria), Increased loss of cells (vomiting, diarrhoea), Decreased dietary intake (anorexia).

pH, Amylase, and Lipase

• Decreased pH: Reduced renal excretion of H+.
• Increase in amylase and lipase: reduced renal excretion and inactivation. Typically mild (up to 3-4x the URL.)

Uraemia

• Refers to urine in the blood, a clinical syndrome caused by loss of kidney function, with multiple metabolic derangements.
• Common signs include vomiting, anorexia , weight loss, diarrhoea, anemia, ulcerative stomatitis, muscle tremors, convulsions, and coma.

Urinalysis (Chemical Examination)

• Detection and quantification of solutes: (amount of solutes and water excreted).
• Dipstick Analysis: Semi-quantitative results (glucose, haem, protein).
• Quantitative Analysis: Urinary protein-to-creatinine ratio (UPCR).

Proteinuria

• Presence of proteins in the urine.
• Many small proteins (Mr < 68,000) pass through the glomerular filtration barrier in healthy animals but are mostly reabsorbed in the proximal tubules.
• Measurable amounts may be present in some healthy dogs.

Proteinuria – What to Do

• Location: Prerenal, renal, or postrenal.
• Magnitude: (UPCR levels)
• Persistence: Persistent proteinuria: indicates glomerulopathy.
• Treatment thresholds: Dogs >0.5; Cats >0.4

Renal Proteinuria

• Proteinuria should be checked for: Location, Persistence, Magnitude (UPCR), >2.0 – Suggestive of glomerulopathy.
• Typical treatment thresholds: Dogs >0.5; Cats >0.4

Glucose in Urine (Glucosuria)

• Relatively small molecules (Mr = 180) that pass freely through the glomerular filtration barrier.
• Reabsorbed in proximal tubules via Na+-glucose cotransporter system—not normally present.
• Hyperglycaemic glucosuria: Serum GLU >10 mmol/L in dogs and >13-16 mmol/L in cats.
• Renal glucosuria: Damaged/abnormal proximal tubules (Fanconi syndrome, proximal tubular toxicosis, etc.)

Haem (Blood) in Urine

• Detects haem-containing compounds like hemoglobin or myoglobin.
• Haemorrhage into the urogenital tract (e.g., cystocentesis—iatrogenic).
• Intravascular haemolysis, in vitro haemolysis (hemoglobinuria).
• Myocyte damage/necrosis (myoglobinuria).

Urine Sediment Examination

• Typically uses 5 ml of urine.
• Wet (unstained) and stained preparations.
  • Erythrocytes
  • Leukocytes
  • Epithelial cells
  • Casts
  • Crystals

Urine Sediment and Examination Findings

• Erythrocytes (haematuria): Low numbers (<5/HPF) in healthy animals. May occur in pathological hemorrhage (UTI, urolithiasis, neoplasia, coagulopathy), latrogenic hemorrhages (during cystocentesis/catheterization), and oestrus.
• Leukocytes (pyuria): Low (<5/HPF) in healthy animals. Typically neutrophils are present. Septic or non-septic inflammatory causes (UTI, urolithiasis, neoplasia). Genital inflammation as a source in voided samples.
• Epithelial cells: Renal tubular, transitional, squamous, and other. Inflammatory, neoplastic, or other pathologies.
• Casts (cylindruria): Cellular moulds composed of mucoproteins (e.g., hyaline, granular, cellular, waxy). May occur with glomerular proteinuria, tubular degeneration or necrosis, and inflammation.
• Crystals (crystalluria): Precipitation of salts (cation + anion). Seen in healthy animals, but presence doesn't always mean urolithiasis. (e.g., calcium oxalate, calcium phosphate, magnesium ammonium phosphate, cystine, amorphous.)

Other Findings in Urine Sediment

• Bacteria
• Fungi
• Parasites (like Capillaria)
• Spermatozoa
• Mucus
• Fat droplets
• Non-specific debris

Test your knowledge on kidney functions, hormones, and associated laboratory tests. This quiz covers essential topics related to kidney health and its role in homeostasis. Perfect for students in biology or health sciences.