Biochemical tests of

renal function

Laboratory diagnostics of 1/ Tests of glomerular function

Assessment of glomerular filtration
renal disorders Assessment of glomerular integrity
2/ Tests of renal tubular functions
3/ Tests of renal endocrine functions

Estimation of glomerular Clearance determinations

filtration rate
1/ Exogenous materials
*Cr-EDTA, *Tc-DTPA, inulin
1/ Clearance determinations
2/ Endogenous material: creatinine
2/ Plasma creatinine U: concentration in urine,
3/ Plasma urea
C= UxV
P: plasma creatinine cc.,
V: Volume of urine 24 h (ml/min)
4/ Plasma level of low molecular weight P: plasma creatinine P
proteins:
β2-microglobulin, retinol binding protein Requirements: free filtration, no reabsorption
Glomerular marker: serum cystatin C and no secretion in the tubules
Problems: urine collection, 2 measurements

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 Old formulae: not adjusted for modern creatinine methods
Estimated glomerular filtration rate: eGFR 1. Cockcroft-Gault formula: no longer applied
eGFR = 1,227[(140 - age) x weight/Scr] (x 0.85 if female)
Body weight (kg), Scr: Serum creatinine cc. in umol/L

1. Modification of Diet in Renal Disease study

group guide line- only 4v MDRD-175 suggested: 2/ Quadratic GFR formula: no longer applied
eGFR=175x(Scr x 0.0113)-1.154 x(age)-0.203x0.742 if female x1.21if black =exp((1,911+5,249/Scrx0,0113-2,114/(Scrx0,0113) 2-0,00686xage-0,205(if
female)) Scr: umol/L
Scr: IDMS calibrated serum creatinine cc. µmol/L, age: year -Tested in healthy controls and CKD patients
-Valid at low plasma creatinine concentrations.
Tested in renal disorders, valid only at high plasma creatinine conc.
-If Scr < 70 µmol/L use 70 mmol/L)

(4v MDRD-186 was used before 2007. for the old Jaffe creat. method) None of the formulae is valid in children (<18)
and in pregnant women.

Classification of CKD based on eGFR Plasma, serum creatinine

-Reliable simple test of glomerular function.
Ref. range of eGFR: 90-120 ml/min./1,73 m2 -Metabolic product of creatine in the muscle
Forming at constant rate, depends on muscle mass.
eGFR:60-90 ml/min./1,73m2mild kidney dis.
-Meat intake may increase serum level by 10%.
Renal failure:
-Creat. is not reabsorbed by the renal tubules but
eGFR: 30-60 ml/minute/1,73 m2 moderate a small amount is secreted.
eGFR: 15-30 ml/minute/1,73 m2 severe New reference range (IDMS): men: 62-106 µmol/L,
eGFR: <15 ml/minute/1,73 m2 end-stage women: 44-97 µmol/L

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 Factors affecting plasma
creatinine concentration Plasma, serum urea
-Simple test that may be informative for GFR.
Age decreased in elder and children
-Major metabolic product of proteins.
Female sex decrease
Race african-americans: increase -Synthesized in the liver from ammonia+CO2.
Diet vegetarian: decrease
cooked meat: increase 90% is filtrated by the glomeruli, neither actively
Body habitus muscular mass: increase reabsorbed nor secreted, min passive reabsorption
malnutrition: decrease
obesity: no change -Urea production depends on nonrenal variables!
Medications increase
-Reference interval: 3.6-7.2 mmol/L (practice book)

Nonrenal factors influencing Cystatin C:sensitive marker of glomerular filtration

plasma urea level -More sensitive and specific indicator of glomerular

function than serum creatinine.
Increase Decrease
-Synthesized in nucleated cells at constant rate
(Low Mw: ~13 kD cysteine protease inhibitor)
High protein intake Low protein intake
Gastrointest. bleeding Severe liver disease
-Filtrated freely through glomerular membrane -
Hypercatabolic state
due to low Mw and high isoelectric point
Dehydration
-Eliminated only by glomerular filtration.
Urinary stasis-slow excretion
- If GFR decreases →Serum Cys C increases

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 Renal protein excretion Relative glomerular
permeability of molecules
Proteins in the glomerular filtrate:
7-10 g/day Molecule M. mass Diameter pI Sieving coeff.
Urea 60 0.54 - 1.0
Urinary protein excretion: Creatinine 113 0.60 - 1.0
- Ref. range <150 mg/day Inulin 5000 2.4 - 1.0
-half of it Tamm-Horsfall Protein (THP) in casts β2-microglobulin 11800 1.6 5.6 0.7
Cystatin C 12800 ? 9.2 0.7
Albumin secretion: < 30 mg/day 24h urine Retinol-binding p. 22000 2.1 4.5 0.7
Today instead of 24h urine, from the1st morning urine α1-microglobulin 30000 2.9 4.5 0.3
Alb/creat. (ACR) suggested: Albumin 66000 3.5 4.7 0.0002
ACR Ref. range (mg/mmol) < 2.5 men, < 3.5 women IgG 150000 5.5 7.3 0.0001

Protein filtration and reabsorption Classification of proteinuria

Protein Plasma Filtrate Urine I. Increased glomerular filtration
β2-microglobulin* 1.5 mg/L 1.1 mg/L 0.1 mg/L
Cystatin C* 1.0 mg/L 0.7 mg/L 0.1 mg/L
Retinol-binding p* 25 mg/L 17.5 mg/L 0.1 mg/L II. Decreased tubular reabsorptive capacity
α1-microglobulin* 25 mg/L 7.5 mg/L 5.0 mg/L
*measured generally in serum
Albumin** 40 g/L 8.0 mg/L 5.0 mg/L
III. Postglomerular secretion or leakage
IgG 10 g/L 1.0 mg/L 0.1 mg/L
Total protein** 70 g/L 700 mg/L 150 mg/L
** High Mw proteins

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 I. Increased filtered load II. Decreased tubular reabsortion

1/ Glomerular: increased glomerular permeability –> 1/ Proximal tubular damage: lower Mw.
progressively increasing excretion of higher Mw proteins.
proteins (RBP, α1-microglobulin) in urine
2/ Overflow proteinuria: increased plasma cc. of
relatively freely filtered proteins (Bence-Jones protein, myoglobin). 2/ Enzymuria:
damage of tubular cells results in increased cell turnover
3/ Decreased glomerular number: increased and cell lysis.
filtered load per nephron- later insufficient filtration. Enzymes origin from brush border, cytosol, lysosomes

III. Postglomerular secretion Investigation of proteinuria

or leakage Screening test for proteinuria: dip-sticks does
not detects albumin (>200 mg/L), less sensitive to
1/ Increased protein secretion by the tubular other proteins (does not detect Bence Jones protein)
system (Tamm Horsfall Protein)
Fals positive reaction: alkaline urine, X-ray
2/ Leakage of plasma proteins into urine: contrast media.
e.g. inflammation caused tubulointerstitial damage
External causes of proteinuria (fever, strain
exercise, orthostatic proteinuria) should be
excluded and define the type of proteinuria.

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 Differential diagnosis of proteinuria Hematuria
Occurrence:
1. Electrophoresis of concentrated urine 1/ Glomerular disease
-Tubular damage: low Mw proteins 2/ Tubulointerstitial disease
-Glomerular: higher Mw proteins are also present 3/ Postrenal disease
Types:
2. Selection of individual protein markers: 1/ rbc-s in the urine
for the assessment of tubular damage: 2/ Hemoglobinuria
-Retinol-binding protein, α1-microglobulin
Detection:
3. Urinary enzyme measurements:
Detection of rbc-s in urine sediment by phase
urinary ALP isoenzyme, urinary NAG index
contrast microscopy
Chemical method-urinary dipstick (hemoglobin)

Assessment of tubular functions Urinanalysis, dipstick testing

1.Assessment of renal concentrating ability after 1/ Protein – lower sensitivity for albumin
water deprivation (urine specific gravity or osmolality) 2/ Hemoglobin: detects rbc and free Hb.
two testpads of different sensitivity
2. Measurement of glucose in plasma and urine 3/ Glucose: detection limit ~3mM, ref.r<0,6mM
(renal glucosuria or not?) 4/ Nitrate: detection of bacteriuria
3. Urinary enzyme measurements: ALP, NAG index 5/ Specific gravity
4. Tests for renal tubular acidosis 6/ pH: 5-8.5 double indicators
fractional bicarbonate excretion 7/ Leukocytes: detection of leukocyte esterase,
ammonium chloride loading test detection limit ~ 10 cells/µL
5.Tests for aminoaciduria Further tests: UBG, bilirubin
HPLC: measurement of amino acids Evaluation: by eyes or by reflectometry

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 Microscopic examination
of urine
1/ Erythrocytes

2/ Leukocytes

3/ Casts:consisting of Tamm-Horsfall Protein,

rbc-s, leukocytes may adhere to their surface

4/ Crystals