Renal-function-tests

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Renal-function-tests

  1. 1. RENAL FUNCTION TESTS By doctoroid
  2. 2. 1) Excretory – primary :by urine formation 2) Regulation of volume & electrolyte composition of ECF 3) Regulation of acid-base balance 4) Endocrine function – produce & secrete: erythropoietin, renin, calcitriol(1,25- DHCC) 5) Site of neoglucogenesis – not primary: in starvations- esp. from glutamine
  3. 3.  collective term for a variety of individual tests and procedures that can be done to evaluate how well the kidneys are functioning.  Primarily reflects two basic mechs.– Glomerular ultrafiltration & Tubular reabsorption/secretion  Practically, divided into 3 groups – 1) Analysis of urine & blood 2) Specific assessment of renal clearance 3) Additional special Tests
  4. 4.  Early detection of possible renal damage & assessment of its severity  Measure progression of the renal impairment & efficacy of corrective therapy  Predict when renal replacement therapy may be necessary  Monitor safe & effective use of drugs, which are principally eliminated through urine.
  5. 5.  A) PHYSICAL : 1)Volume > 800-2500 ml/dintake~2.5 L/d  Polyuria >2.5L Chronic GN  Anuria ,Oliguria 2) Appearance > clear  Turbid (alkalinity d/t prolonged standing l/t ppt of Ca/Mg-phosphates,↑phosphate , presence of pus d/t UTI)
  6. 6. 3) Colour> straw/amber-yellow urochrome  Brownish yellow (jaundice)  Dark (alkaptonuria)  Reddish brown (RBC/Hb/Mb-uria,Porphyria etc.) 4) Odour> mild aromatic  volatile org. acids  Unpleasant ammoniacal (prolonged standing)  Acidotic fruity (DKA)
  7. 7. 5) Sp. Gravivity & Osmolality >  1.003 to 1.030 & 50-1200 mOsm/kg (depends on state of hydration of the body)  Early morning urine sample(=after overnight fast)if SG>1.018 & Osm>600 ≡Normal  SG is simplest to measure but unreliable(in presence of HMW substances) for evaluating renal concentrating ability.  SG  decreased,increased & fixed(1.010=CRF)
  8. 8. 1) Reaction > mild acidic  pH avg.6 (=4.5- 7.5)  normal short PP alkaline tide  Protein rich diet  acidic  Vegetable rich diet  alkaline also in type II DTA, UTI by urease producing organisms, Acetazolamide therapy, alkali ingestion.
  9. 9. 2) For abnormal urinary constituents : I) Proteins >  Normal upto 150 mg/d—routinely undetected  Proteinuria  albumin predominates  By– a) heat & acetic acid test b) Sulphosalicylic acid test c) Esbach’s albuminometer
  10. 10. II) Reducing Sugars >  Normally absent – glucose/fructose/galactose  When renal threshold is exceeded  By Benedict’s Test III) Blood >  Normally does not appear  By Benzidine Test
  11. 11. IV) Ketone Bodies >  Normally not present  By- Rothera’s Test & Gerhardt’s test. V) Bile salts >  Only in early phases of obstructive jaundice  By- Hay’s test & Petenkoffer’s test
  12. 12. VI) Urobilinogen > N ~1 - 3.5 mg/d  ↑ in persistent fevers, hepatobiliary diseases, haemolytic jaundice  By- Ehrlich’s test & Schlesinger’s test VII) Bile-pigments >  Bilirubinuria=↑conj.Bilirubin  hep/post-hep jaun  By- Modified Fouchet’s Test
  13. 13. Imp findings in the urinary sediment includes--- I) Casts >> proteinaceous plugs  Formation favoured by sluggish flow  Various shapes c/t tubules in which formed cellular or non-cellular  Types  Hyaline, RBC, WBC, Granular, Broad waxy etc.
  14. 14. II) Crystals >>  Ca-oxalate/phosphate, Triple phosphate-- common  May be normally found  risk of stone in future  Urate or Cysteine crystals  pathologic III) Cells >>  RBCs, WBCs, pus cells, Sq.epithelial, Tubular epithelial cells
  15. 15.  Strip impregnated with reagents for the substances in question within a urine sample.  By comparing the colour-change(in the paper- squares)with the standardized colour-charts.  Modern dipsticks with multiplied zones:  Can detect/measure: Protein, hemoglobin, glucose, urobilinogen, ketones, leukocytes, specific gravity, and pH  A promising tool everywhere at the level of primary care!!!
  16. 16.  There is no plasma constituent whose conc. depends solely on the functionality of kidneys.  Frequently used are 2 normal metabolic wastes  Excreted by kidneys  accumulates in renal dysfunction  ↑blood levels I) Blood Urea Nitrogen >> 8-25 mg%  begin to rise only after 50% renal damage II) Plasma Creatinine >> 0.6 – 1.5 mg%  More reliable as BUN is subjected to variations
  17. 17.  Vol. of plasma that is cleared of a substance in unit time, by its’ urinary excretion ml/min  Calculated as: C = UV/P  Predominantly determine GFR: Relationship as —  Correlated more directly with the status of kidney function  employed to assess GFR,RPF & GFR = C No reabs, No Secret INULIN GFR > C Much reabs, No Secret Gluc, AA, Na+, Cl- GFR < C No reabs, Much Secret PAH, Diodrast
  18. 18.  Characteristics of an Ideal Marker :  Constant rate of production (or for exogenous marker can be delivered IV at a constant rate)  Freely filterable at the glomerulus (minimal protein binding)  No tubular reabsorption/secretion  No extrarenal elimination or metabolism  Availability of an accurate & reliable assay  For exogenous markers-- safe, convenient, readily available, inexpensive & physiologically inert
  19. 19. Various markers used : A) Exogenous >> 1) Inulin (gold standard but technically demanding) 2) Non-radiolabelled contrast media (e.g. Iohexol) 3) Radiolabelled compounds (e.g. 99m Tc-DTPA) B) Endogenous >> 1) Creatinine (marginally overestimates—most widely used in clinical practice) 2) Urea (one of the 1st markers– not used at present)
  20. 20.  Approximation of bedside GFR with limited accuracy by “Cockroft & Gault formula”  Most widely used & best validated for adults Ccr =(140-Age)x(Wt in Kg)/(Plasma Creatinine x72)  [Correction factor for females = 0.85]  value to such formulas for GFR prediction is likely to increase when an accurate plasma creatinine assay is performed along with inhibition of tubular secretion by cimetidine/probenecid.
  21. 21. Applying “Fick’s Principle” to kidney : Amount of a sub excreted by kidney in unit time(UV) =RPF X renal A-V diff. in its plasma conc.(Pa - Pv)  RPF(ml/min) =UV / (Pa - Pv)  Criteria of the marker to be used :  Almost totally extracted from plasma with each passage through kidney  Not metabolised/stored/produced by kidney
  22. 22.  Use of PAH Clearance to measure RPF/RBF:  Cont. low dose PAH inf. plasma conc. Constant  All PAH excreted in urinePv(PAH)=0eliminated  ≡> RPF = UV/Pa(PAH) = Clearance of PAH(C-PAH)  10% RPF perfuses non-excretory portionsERPF  True RPF = ERPF/0.9  RBF = true RPF / (1 – Haematocrit value)  Normal ERPF = 600-650 ml/min/1.73 sq.mt BSA
  23. 23. A) TESTS FOR TUBULAR FUNCTIONS: I) Urine Conc. Test >> Early dinner  no food/fluid after 6 PMbladder emptied @ 7AM  discarded specimens collected @ 8 AM & 9AMatleast one should hv SG >1.022 or Osm >850 mOsm/kg II) Vasopressin test >> No fluid after 6 PM s.c. ADH(5U)inj.@8PMurine samples collected separately till 9AMatleast one should SG>1.020 or Osm>800
  24. 24. III) Urine Dilution Test >> Pt. completely empties bladder after overnight fast drinks 1L waterhourly urine specimens collected for next 4 hrsatleast 700ml will be excreted & atleast one should hv SG <1.004 IV) Urine Acidification Test >> Fasting from midnightcomplete bladder emptying @morningOral Am.Cl.(0.1gm/kg) with 1L water given hourly urine samples collected for next 6 hrs. atleast one should hv pH of 5.3 or less
  25. 25. V) Dye Excretion Test or PSP Test>>  Phenolsulphonphthalein(Phenol red)— filtetred & secreted.  600 ml water drink f/b IV 6mg PSPhourly urine samples collected40-60% should be excreted in 1st hr. & another 20-25% should excrete in 2nd hr  Excretion<50% over 2hrs. abnormal
  26. 26. VI) Other Sophisticated Methods>>  MICROPUNCTURE techniques  MICROCRYOSCOPIC studies  MICROELECTRODE studies VII) Renal Biopsy >>  Specimen subjected to LM,EM & IFM-studies  ↑knowledge & better understanding of renal
  27. 27.  Plain radiograph of abdomen  IVP  USG, CT Scan, MRI Scan  Radionuclide studies  Strictly speaking, these are not considered to be RFTs, but very useful in present day clinical practice for structural & functional assessment of kidneys.

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