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• Non-protein nitrogen measures the kidneys ability to get rid of waste products
• renal functions include fluid balance, excretion, hormone synthesis, metabolic function, and acid/base balance
• • Fluid balance of kidneys occurs via selective regulation of electrolytes 
• • Albumin and sodium have largest influence on fluid regulation in the body
  • Albumin isn’t excreted, so kidneys cannot regulate albumin; however, can regulate sodium 
• • Excretion of unwanted products in the kidney include urea, ammonia, excess minerals, toxins, poisons, drugs
• • Hormone synthesis of kidneys include renin, erythropoietin, prostaglandins
• renin is responsible for BP regulation
• erythropoietin is responsible for regulation of red cell production
• prostaglandins increase renal blood flow, sodium and potassium excretion, regulates renin release
• Metabolic function of kidney includes breaking down or deactivating some hormones, activates vitamin D, plays a role in gluconeogenesis
• • acid/base balance of kidney includes conserving bicarbonate ions and removes hydrogen ions and metabolic acids 
• when urea is in blood or plasma, it is called BUN (blood urea nitrogen)
• ammonia comes from the deamination of amino acids; is cytotoxic
• bruh

  A) O

  B) H2N

  C) NH2

  
•  historic assays based on nitrogen content, hence the name BUN and not blood urea
• in postrenal azotemia, Blood going through efferent arteriole will have same composition of afferent arteriole 
• • Decreased BUN levels can be caused by decreased protein intake, severe liver disease (will not form urea), vomiting, diarrhea, and pregnancy 
• GLDH coupled enzymatic reaction

  • Looking at change of absorbance via oxidation of NAD+; most likely kinetic assay 
  • Urease in reagent 
  • Urea and water in sample
• in first step of urease assays, Urease breaks down urea into original components of ammonia and CO2 (enzymatic)
• • Change of pH will give color change as ammonia is a strong base

  A) NH3+

  B) pH indicator

  C) color change

  
• • Unionized urea to ammonia and bicarbonate leads to increase conductivity
  • Urea doesnt have charge, but when broken down into components, both have charge and will conduct electricity
• Diacetyl monoxide assay of urea - in acetic buffer; uses toxic reagents
• Interferences for urea: hemolysis
• •  Creatine is synthesized in the liver 
• Creatinine is released along with CK in muscle damage into blood; we do not look to measure creatinine for muscle damage (will use creatine kinase)
• creatinine is used for routine analysis of metabolic function
• • 2 methods of metabolism: Creatine loses water molecule and becomes creatinine and Creatine phosphate loses a phosphoric acid
• to measure renal function, creatinine can be measured through creatinine clearance, glomerular filtration rate, and tubular secretion testing
• • Creatinine clearance - Volume of plasma cleared completely of a substance per time (how much blood is cleared of its creatinine of a unit of time [usually 24 hours])
• • Glomerular filtration rate - measuring of a substance that is exclusively filtered by the glomerulus and not reabsorbed 
• • Tubular secretion testing - what is being put into filtrate by proximal/distal tubule; what is passed from capillaries to tubules, not purposely filtered out by kidneys
• in tubular secretion testing, the chemical marker p-aminohippurate is used; will not be filtered out by glomerulus but will be secreted into filtrate
• in tubular secretion testing, p-aminohippurate is infused and is measured in both urine and serum
• • Creatinine clearance procedure
  • 24-hour urine (refrigerated during collection)
  • Serum creatinine collected sometime during 24 hour period
• creatinine clearance is used for monitoring, not diagnosing kidney issue
• EGFR - Estimated glomerular filtration rate
• eGFRs are done in pts 18 or older
• Normal eGFR: >60 mL/min per 1.73 m^2
• 1.73 m^2 is the average body surface area - perspiration can affect