![Plasma creatinine vs. GFR
not linear, hyperbolic correlation!
GFR
[pCreat]
140 mL/min
(100%)
0 mL/min
(0%)
Change within an
individual patient is usually
more important than the
absolute value](https://image.slidesharecdn.com/renalfunctions-230828132717-1f572106/85/Renal-functions-ppt-22-320.jpg)
Renal functions.ppt
- 1. Renal function- basic data for students and residents Department of Paediatrics Section for Pediatric Nephrology University Hospital Motol, Prague
- 2. Functions of the kidney regulation e.g. homeostasis, water, acid/base excretion e.g. urea, creatinine endocrine e.g. renin, erythropoietin, 1,25 dihydroxycholecalciferol- conversion only in kidney!
- 3. Renal function tests detect renal damage monitor functional damage help determine etiology
- 4. Laboratory tests of renal function glomerular filtration rate (GFR) plasma creatinine plasma urea urine volume urine urea minerals in urine urine protein urine glucose hematuria osmolality
- 5. Kidney Function A plumbers view Filter Processor Input Arterial Output Venous Output Urine
- 6. Kidney – basic data Urine excreted daily in adults: cca 1.5L Kidney only ca 1% of total body weight, despite it The renal blood flow= 20% of cardiac output Plasma renal flow= PRF ca 600 mL/Min./1.73 M2 Reflects two processes Ultrafiltration (GFR): 180 L/day Reabsorption: >99% of the amount filtered
- 7. How do you know it’s broken? Decreased urine production Clinical symptoms Tests Filter Processor Input Arterial Output Venous Output Urine
- 8. Where can it break? Pre-renal Renal (intrarenal) Post-renal (obstruction) Filter Processor Input Arterial Output Venous Output Urine
- 9. Causes of kidney functional disorders Pre-renal e.g. decreased intravascular volum Renal e.g. acute tubular necrosis Postrenal e.g. ureteral obstruction
- 10. Tests of renal function glomerular filtration rate=GFR plasma creatinine= Pcr plasma urea-Purea urine volume= V urine urea- Uurea cystatin C in plasma? urine protein urine glucose hematuria osmolality
- 11. Renal Function Tests- Urine volumes Adults: 1.5 L/24 h typical in health, oliguria < 400 mL, anuria < 100 mL, polyuria > 3000 mL Children: ca 1.5 ml/Kg of b.w./1 hour!
- 12. Principle of of Clearance Some substances when filtered enter the tubules are not reabsorbed and so 100% excreted= GFR (inulin= gold standard for GFR, creatinine (but this one partially reabsorbed, particularly in uremia, then clearance <GFR Some substances are filtered, enter tubules, and more of the substance is secreted enters the tubules by excretion. Clearance>GFR Some substances are filtered, enter tubules, but are completely reabsorbed, so they did not reach the final urine (e.g. cystatin C)
- 13. Glomerular filtration rate Glomerular filtration= major physiologic responsibility of kidney, GFR used as index of overall excretory function Methods: clearence of inulin, creatinine, EDTA and DTPA (=both derivates of acetic acid), cystatin C GFR= Ux x V (V=volum of urine/ 1 minute or 1 second) P x x= clearence of substance used
- 14. Glomerular filtration rate Also service of nuclear medicine dptm. Follow up the inulin clearence, EDTA or DTPA clearence labelling the substances with chromium or Tcm99 Where will you catch the activity with detectors? Never in the kidney or bladder area!!
- 15. Glomerular filtration rate GFR in children, value always adapted to the BSA!! Ideal BSA in adults is 1.73m2 Schwartz equation : GFR= v x 0.808 P cr (umol/L) How to assess easy if plasma creatinine is OK? Pcr max= Vcm x 0.61 (v= body height in cm
- 16. Creatinine and Urea Plasma Concentration- hyperbolic correlation GFR 50% pCr, pUrea 140 mL/min (100%) 0 mL/min (0%) Tendency in individual patients is more important than the one value, ever test if the hydration is OK. In patients with CRI always note also the BSA! Lower limit today not 80 ml/Min. /1.73 m2 but 90 ml/Min./1.73 m2 Normal range->
- 17. Plasma urea (BUN) = BUN (blood urea nitrogen) Urea: product of protein catabolism Synthesized by liver, majority excreted by kidney, partially reabsorbed in tubuli Plasma concentration increases with decreased GFR
- 19. Enzymatic conductivity rate method for measuring urea Urease solution Urea + 3H2O HCO3¯ + 2NH4 + OH¯ urease
- 20. Urea in patients with kidney diseases Useful test but must be interpreted with great care, urea plasma level is more than creatinine dependent on protein intake Most useful when considered along with creatinine High in high protein intake, low in severe liver dysfunction Urea EF may be useful in pts. on diuretics
- 21. Plasma creatinine and renal functions Creatine: main storage compound of high energy phosphate needed for muscle metabolism. Creatinine: anhydride of creatine! Creatine Creatinine (Waste product) H2O
- 22. Plasma creatinine vs. GFR not linear, hyperbolic correlation! GFR [pCreat] 140 mL/min (100%) 0 mL/min (0%) Change within an individual patient is usually more important than the absolute value
- 23. Jaffe´ reaction for measuring creatinine, simple, but better is enzymatic method Creatinine + alkaline picrate solution Bright orange/red colored complex absorbs light at 485nm (many interfering substances in blood Can be minimized using rate method)
- 24. Analytical methods (Cr) Normal range Pcr Male 0.6-1.2 mg/dL, Female 0.5-1.0 mg/dL Be careful in children!! Remember the max. plasma creatinine value!!
- 25. BUN: creatinine ratio Pre-renal disorders BUN:Cr ratio >20 Renal disorders BUN: Cr nl but both elevated Post-renal Filter Processor Input Arterial Output Venous Output Urine
- 26. Osmolality of urine Measures urine concentrating ability Depends on # of particles, not size or charge Largely due to ADH (anti-diuretic hormone) Can reach maximum of 1200 mOsm/L Normal range: 300-900mOsm/L, plasma 285+10 prior to collection, fluid intake restricted, first void submitted for evaluation Measuring using the fact of freezing point depression
- 27. Standardized renal concentration capacity test 1. Voiding completely at 9 p.m. (WC) 2. Desmopressin administration (since 2006 as nasal spray). DDAVP is a Czech invention !! 3. Collection of urine (9 p.m. – 7 a.m.) 4. Testing of urine osmolality in this sample (not the morning urine only!) 5. The lower limit of normal value= 950 mOsm/kg of urine 6. Short testing- Desmopressin, collection for 4 hours only= at least 900 mOsm/kg of urine
- 28. Urine dipsticks Strip impregnated with reagents for the substances in question within a urine sample Substance level can be altered in the setting of pathology within the urinary tract Measured substances: Modern dipsticks with multiplied zones: Protein, hemoglobin, glucose, urobilinogen, nitrite, leukocytes, specific gravity, and pH Should be a tool everywhere on the level of primary care!!!