LABORATORY INVESTIGATION LABORATORY INVESTIGATION ON ON

RENAL DISORDERSRENAL DISORDERS

Rahajoe Imam SantosaRahajoe Imam SantosaConsultant Clinical Pathologist

CLINICAL LABORATORY UPDATE III - 2008CLINICAL LABORATORY UPDATE III - 2008

RENAL FUNCTION TEST

Renal FunctionRenal DiordersRenal Function TestGFRLaboratory AspectSummary

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RENAL FUNCTIONS

• Filtration• Re-absorption • Secretion• Excretion• Regulation• Metabolic• Endocrine

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CAUSES OF RENAL FAILURE

PRERENAL : • Cardiogenic and hypovolemic shock 

RENAL : • ACE-inhibitors and NSAID´s impair renal autoregulation• Fulminant hypertension

• Renal artery stenosis and embolism

• Vasculitis in glomerular capillaries

• Renal vein thrombosis

•Toxic tubular damage (organic solvents, myoglobin, aminoglycosides, and X-ray contrast)

RENAL DISORDERS

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POSTRENAL : (Obstructions of the lumen, the wall and by pressure)

• Lumen: Tumors, calculus and blood clots within the lumen of the renal pelvis, ureter, and bladder

• Wall: Strictures of the ureter, the ureterovesical region, urethra, and pinhole meatus

• Congenital disorders such as megaureter, bladder neck obstruction, and urethral valve

• Neuromuscular dysfunction in the urinary tract

• Pressure: Compression by tumours, aortic aneurysm, retroperitoneal fibrosis or gland enlargement, retrocaval ureter, prostate hypertrophy, phymosis, and diverticulitis

RENAL DISORDERS

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• Older age• Family history of CKD• Decreased renal mass• Ethnicity• Diabetes Mellitus (DM)• Hypertension• Autoimmune Diseases• Infections (systemic, urinary tract)• Nephrolithiasis• Obstruction to the urinary tract• Drug toxicity

RISK FACTORS

RENAL DISORDERS

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• Blood Urea Nitrogen (BUN)• Creatinine• Creatinine Clearance• Glomerular Filtration Rate (GFR)

• Cockroft-Gault equation• MDRD (Modification of Diet in Renal

Disease) equation• Urinalysis• Uric acid

RENAL FUNCTION TEST

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RENAL FUNCTION TEST

• Fractional Excretion of Sodium (FENa)• Fractional Excretion of Urea (FEUrea)• Electrolytes (Na, K, Cl, Ca, P, Mg)• Urine concentrating ability• Urine/plasma osmolality• Urinary Anion Gap {(Na++ K+) – Cl-}• Tubular function tests• Associated tests (hormones, CBC, etc)

• Urea is a relatively nontoxic substance made by the liver to dispose of ammonia resulting from protein metabolism• The real urea concentration is BUN x 2.14• Normal BUN range is 8-25 mg/dL• BUN is a sensitive indicator of renal diseases

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BUN (BLOOD UREA NITROGEN)

RENAL FUNCTION TEST

RENAL FUNCTION TEST

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• The breakdown product of creatine phosphate released from skeletal muscle at a steady rate• Amount produced relates to muscle mass (1-2%/day of muscle creatine converted to creatinine)• Freely filtered by the glomerulus and some tubular excretion• Generally a more sensitive and specific test for renal function than the BUN• Normal range is 0.6-1.3 mg/dL

CREATININE

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CREATININE v/s GFR

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RENAL FUNCTION TEST

CLEARANCE

• A timed urine sample and serum sample used to approximate the glomerular filtration rate• It is not an exact measure of the GFR because some is not filtered and some is secreted into the proximal tubule• In health these cancel each other out, when the GFR drops below 30mL/min the tubular secretion exceeds the amount filtered and can give a false elevation

• Incomplete urine collection• Assess adequacy of collection from steady state creatinine

• Adult ages < 50 years (lean body weight)• Male 20-35 mg/kg and females 15-20 mg/kg has a daily creatinine excretion

• Adult ages 50-90 years (lean body weight)• progressive 50% decline in creatinine excretion

RENAL FUNCTION TEST

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ERRONEOUS VALUES IN CLEARANCE

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◦Appearance◦Specific gravity◦Osmolality◦pH◦Glucose◦Protein◦Urinary sediments

RENAL FUNCTION TEST

URINALYSIS

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FeNa= Amount of Na excreted Amount of Na filtered

FeNa= UNa x Urine volume PNa x GFR

FeNa = UNa x V PNa x[(UCr x V) /PCr]

FeNa % = UNa x PCr X 100 PNa x UCr

FRACTIONAL EXCRETION OF FILTERED SODIUM (FENa)

RENAL FUNCTION TEST

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Measures urine concentrating ability Depends on the quantity of particles, not size or

charge Mainly due to ADH Normal range : urine : 300-900mOsm/L plasma : 285+10 mOsm/L Prior to collection, fluid intake restricted, first

void submitted for evaluation Measuring using osmometer (the fact of

freezing point depression)

OSMOLALITY OF URINE

RENAL FUNCTION TEST

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Proximal Tubular Function◦ Phosphate re-absorption◦ Aminoaciduria◦ Glucosuria◦ Fractional HCO3

- excretion

Distal Tubular Function◦ Acidification (Ammonium chloride load)◦ Concentration (Water deprivation test)

TESTS OF TUBULAR FUNCTION

RENAL FUNCTION TEST

GLOMERULAR FILTRATION RATE

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GFR >45 ml/min symptom less except for underlying pathology and hypertension

GFR <45 ml/min tiredness, diminished well being

GFR <30 ml/min anaemia, metabolic abnormalities e.g. acidosis, Ca/PO4 homeostasis

GFR <15 ml/min nausea, vomiting and gastritis

GFR <10 ml/min cardiovascular and neurological symptoms

GFR <5 ml/min End Stage Renal Disease

RENAL DISORDERS

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the best estimate of the number of functioning nephrons or functional renal mass

an excellent measure of renal filtering capacity

fundamental to the glomerular pathology management of drug therapy (through

glomerular clearance) monitoring of the progression to ESRD to

facilitate timely management decisions monitoring of the adequacy of renal

replacement therapy

CLINICAL USE

GLOMERULAR FILTRATION RATE

NKF, Am J Kid Dis, 39,2(Suppl1), 2002

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COMPOUNDS USED TO MEASURE GFR

Should not be metabolized, or alter GFR Should be freely filtered in the glomeruli, but

neither reabsorbed nor secreted Inulin (a polysaccharide) is ideal Creatinine is most popular

◦ There is some exchange of creatinine in the tubules, as a result, creatinine clearance overestimates GFR by about 10%

Urea can be used, but about 40% is (passively) reabsorbed

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• COCKCROFT-GAULT FORMULA• Calculated Creatinine Clearance/GFR

(140–age) x wt (kg) 72 X serum creatinine(mg/dl)

For females, subtract 15% (or multiply by 0.85)

*Applicable only when patient is in a steady state, not edematous, not obese and normal muscle mass and activity

ESTIMATED GFR (eGFR)

GLOMERULAR FILTRATION RATE

ESTIMATED GFR (eGFR)

• May be less accurate in certain populations• Normal or near normal renal function• Children• >70 years of age• Ethnic groups• Pregnant women• Unusual muscle mass• Morbid obesity

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GLOMERULAR FILTRATION RATE

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Cysteine proteinase inhibitor C (MW:13000) Small size, freely filtered by glomerulus Constant production rate by all nucleated cells No known extra-renal excretion routes Correlation of 1/[cystatin C] (r = 0.81) with Cr-EDTA clearance is better than 1/[Plasma Creatinine] (r = 0.51) Not influenced by muscle mass, diet or

subjects sex

CYSTATIN-C

Newman et al , Kidney Int 1995;47:312-318

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• specific and sensitive parameter for glomerular filtration rate

• independent from urine collection, only one serum sample

• no interference by various drugs or other factors

• fast, accurate and simple method for assessment of glomerular filtration rate

CYSTATIN-C

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• Urea

• 24 hr Clearance Creatinine

• Creatinine

• Cystatin C (?)

• CCr calculated from Cr (Cockcroft-Gault)

• GFR calculated from Creatinine

• 3 hr CCr with Cimetidine

• Direct GFR measurement

51Cr-EDTA , Inulin and Iohexol clearance

Inaccurate

Accurate

RENAL FUNCTION TESTS

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• Biological variable• fasting state• postural change• seasonal variations• diet habit, etc.

• Analytical variable• pre-analytical factors• analytical factors• post-analytical factors

FACTORS AFFECTING LAB. RESULTS

LABORATORY ASPECT

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• Imprecission CV (coefficient of variation)

Inaccuracy Bias (from target value)

Total laboratory error TE = % bias + 1.96 CV Goal is <10%

(bias ≤ 4% and CV ≤ 3%)

CLINICAL LABORATORY PERFORMANCE

LABORATORY ASPECT

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Interferences :• Glucose• Uric acid• Ketones• Ascorbic acid• Cephalosporins

Influenced by :• Muscle mass• Weight• Height• Sex• Age• Food intake

LABORATORY ASPECTCREATININE (JAFFE METHOD)

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Fuller’s Earth (aluminum silicate, Lloyd’s reagent)◦ adsorbs creatinine to eliminate protein

interference Acid blanking

◦ after color development; dissociates Janovsky complex

Pre-oxidation◦ addition of ferricyanide oxidizes bilirubin

Kinetic methods o Creatinase, Creatininase, Creatinine

deaminase (iminohydrolase)

MODIFICATIONS OF THE JAFFE METHOD

LABORATORY ASPECT