Kidney Function and Non-Protein Nitrogen Compounds

Kidney Function and Non-Protein Nitrogen Compounds

• Kidneys are bean-shaped organs found in vertebrates, located in the retroperitoneal space.
• In adults, they are about 11 cm long.
• Kidneys receive blood from renal arteries and send blood out through renal veins.
• The ureter carries urine from the kidneys to the bladder.
• The nephron is the functional unit of the kidney, responsible for urine formation (filtration, secretion, and reabsorption).
• Each kidney contains roughly 1.25 million nephrons.
• Kidneys are responsible for eliminating waste products and regulating plasma and water volume, maintaining ionic balance, and regulating acid-base balance.

Kidney Functions

• Elimination of metabolic waste products: Kidneys are the major excretory organs of the body, responsible for removing waste and toxic metabolites. This is carried out through urine formation.
• Regulation of plasma and water volume: Kidneys play a crucial role in maintaining the appropriate volume and composition of the blood and interstitial fluids, by adjusting the water and solute content of the blood.
• Regulation of ionic equilibrium: Kidneys regulate the concentration of various electrolytes.
• Maintenance of acid-base balance: Kidneys, along with the lungs, work together to maintain optimal pH levels.

Clearance Tests

• Inulin clearance test: Considered the most accurate measure of glomerular filtration rate (GFR). Involves IV transfusion and multiple urine samples.
• Creatinine clearance test: Often used to estimate GFR, particularly for patient muscle mass assessment. It's sensitive to kidney function, but not perfectly reliable.
• Urea clearance test: Measures the clearance of urea from the blood. Less reliable than creatinine, given variable urea reabsorption in the nephron.

Other Tests

• Cystatin C: Produced by all nucleated cells, not secreted, but completely reabsorbed. Used as an indicator of GFR. Levels increase more rapidly than creatinine in early stages of GFR problems.
• Beta-trace proteins: Function as prostaglandin synthase, easily filtered and reabsorbed. Elevated levels can indicate myeloproliferative and lymphoproliferative disorders, inflammation and renal failure.
• Myoglobin: Associated with acute skeletal muscle injury. Used as a potential marker of myocardial infarction and rhabdomyolysis.
• Microalbuminuria: Small amount of albumin in the urine, which typically isn't present. An indicator of kidney problems.
• Phenolsulfonphthalein (PSP) test: Measure renal tubular mass based on dye excretion.
• Specific Gravity: Measures concentration of solutes in the urine. High values indicate more concentrated urine.
• Osmolality: Reflects the total number of solutes in a solution. Useful for assessing water balance.

Non-Protein Nitrogen (NPN) Compounds

• Urea, uric acid, creatinine, and others are NPN compounds that are waste products from protein metabolism.
• Elevated NPN levels suggest impaired kidney function. Tests (such as BUN and others) aid in kidney disease diagnosis and assessment of treatment efficacy.

Blood Urea Nitrogen (BUN)

• A screening test for kidney disease. Elevated BUN generally indicates kidney problems.
• Used in evaluating renal function and hydration status, and to assess responses to dialysis therapy.

Creatinine

• A waste product produced by muscle metabolism.
• Its levels in the blood are a good indicator of glomerular filtration rate (GFR).

Uric Acid

• The major end product of purine metabolism.
• Elevated levels can lead to gout (inflammation of joints) and kidney stones.

Azotemia

• Elevated levels of nitrogenous waste products in the blood, often due to impaired kidney function.
• Azotemia can be classified as pre-renal, renal, and post-renal.