Renal Function Test

Dr C. L. Tengtengcl@gmail.comFamily Medicine

IMU Clinical School

23rd Nov 2010, IMU Bukit Jalil

Learning outcomes

• Describe common tests on urine and compare between urine dipstix and microscopy for diagnosis of renal diseases.

• Compare blood urea and creatinine levels in the assessment of renal impairment.

• Identify different ways of imaging renal tracts and their common abnormalities.

• Describe how renal biopsy is done.

Urine test

• Urinalysis– Quantity

– Colour

– Specific gravity*

– pH*

– Protein*

– Others (ketone, glucose, bilirubin)*

• Microscopy– RBC**

– WBC**

– Cast

– Crystal

– Bacteria**

* Can be measured by dipstix (e.g. Combur-10)** Can be tested using dipstix (indirectly)

Urine volume and colour• Urine volume: 700 – 2500 ml/day

(Glomerular filtrate = 180 L/day)– Oliguria: <400 ml/day

– Anuria: <100 ml/day

• “Smoky” urine - small amount of blood (e.g. AGN)

Patient 1: A 50 year-old man with severe left loin pain and haematuria

Patient 2: A 10 year-old girl with facial puffiness, hypertension and

“cloudy urine”

Patient 3: A 45 year-old man who ate jering

• A healthy 45-year-old Sarawakian man presented with colicky left loin pain, dysuria, frank haematuria and foul smelling urine a day after ingesting jering. He developed oliguria and was anuric by the 3rd day.

• Serum creatinine 176 μmol/L, urea 18 mmol/L, potassium 4.4 mmol/L and bicarbonate 21.1 mmol/L.

Abnormal urine colour may not be due to renal disease

Urine dipstix

• Reagent strips allowing 1 or more tests.

• Semi-quantitative.• Quick screening test.• Less accurate when

compared with microscopy.

blood

Renal concentrating ability

• Normal SG: 1.002 – 1.025• Proportional to urinary concentration of

urea and sodium• Renal concentrating ability is normal if SG

> 1.018• In CRF, SG fixed at 1.010 (= glomerular

filtrate)

Renal acidifying ability

• Normal pH < 7.0

• Renal acidifying ability is normal if urine

pH < 5.5

• Acidosis occurs only in advanced CRF.

• In renal tubular acidosis, urine pH exceed 5.4 after given ammonium chloride (i.e. failure to acidify the urine following an oral acid loading challenge).

Two children with facial puffiness

Acute post-streptococcal glomerulonephritis

4 year-oldBP 80/40 mmHg (normal)UrinalysisProtein: 3+Blood: negativeWBC: negativeRBC: negative

10 year-oldBP 150/100 mmHg (high)UrinalysisProtein: 2+Blood: positiveWBC: 1+RBC: 2+

Nephrotic syndrome Nephritic syndrome

ProteinuriaNormal Proteinuria “Massive” proteinuria

24 H urine protein <300 mg/day >300 mg/day >3.5 g/day (nephrotic)

Urine protein dipstix: negative to trace ≥1+ ≥3+

Normal Microalbuminuria Albuminuria

Urine protein dipstix: negative negative/trave ≥1+

24 H urine albumin <30 30-300 >300 mg/day

ACR (mg/mmol) M: <2.5 M: 2.5-30 F: <3.5 F: 3.5-30

ACR=Albumin:Creatinine ratio

Urine microscopy

Urine microscopy - blood

• Overtaken by automated test with dipstix

• Centrifuged urine has– < 1 rbc/hpf– < 5 wbc/hpf

• Dipstix can’t differentiate between haematuria and haemoglobinuria

www.udel.edu/medtech/mclane/csmain.html

Colour: AmberProtein: 1+Blood: 2+WBC: 1+RBC: 2+

A 56-y.o. woman with oedema, decreased urine volume, fever, general malaise and abdominal pain

WBC: 5-10/hpf RBC: 10-20/hpf Celluar casts:  0-2/lpf

Dysmorphic RBC = glomerular bleeding (GN)

High power light microscopy

A Normal rbcB-F Dysmorphic rbc(Scanning electron microscopy)

Acanthocytes – specific for glomerular bleeding

Phase contrast microscopyx1450 x3250

http://content.nejm.org/cgi/ijlink?linkType=FULL&journalCode=nejm&resid=334/22/1440

Urine microscopy – WBC, bacteria

• Pyuria – infection or injury of renal tract.

• Bacteria can be detected by gram stain.

• Most UTIs are caused by gram –ve bacteria (E. coli)

• Dipstix detects WBC by leucocyte esterase reaction.

• Positive nitrite in dipstix suggests significant bacteriuria (>105 organisms/mL)

• Gram –ve bacteria reduced nitrate to nitrite.

Microscopy – casts

Hyaline cast Granular cast Waxy cast

Red cell cast White cell cast Broad cast

Microscopy – casts

• Hyaline cast – normal

• Red cell cast – GN

• White cell cast – GN, pyelonephritis

• Epithelial cast – acute tubular necrosis

• Broad cast – chronic renal failure

• Granular cast, waxy cast – renal disease

Microscopy – crystals

Ammonium magnesium Phosphate crystals

Calcium oxalate crystals

Cystine crystals Urate crystals

“normal crystals”

“abnormal crystals”

Can I trust the test result?

• Urine collection: early morning midstream clean catch urine.

• False positive: blood in urine may be due to contamination (menstruation in female).

• False negative: nitrite negative may be due to dilute urine.

Positive test = Disease present?

Disease

present

Disease

absent

Test positive TRUE POSITIVE

FALSE POSITIVE

Test negative FALSE NEGATIVE

TRUE NEGATIVE

Estimation of GFR

• Normal GFR is 70-170 ml/min (varies with sex, weight and surface area).

• Blood urea and creatinine levels are good substitutes in clinical practice

Blood urea

• Normal range is 2.5 – 6.6 mmol/L.

• Its level varies with protein intake.

• Raised by dehydration, fever and GI haemorrhage.

• 50% of filtered urea is reabsorbed.

• Very high level correlates well with uraemia.

Serum creatinine

• Normal range is 62 – 124 mol/L (0.7-1.4 mg/dL)

• Level less affected by extrarenal factors.• Serum creatinine correlates better with GFR

than blood urea.• Creatinine clearance declines by 1 ml/min/y

over the age of 40 (aging process).

Reciprocal relationship between creatinine clearance and plasma creatinine concentration

GFR calculatorhttp://www.kidney.org/professionals/KDOQI/gfr_calculator.cfm

Classification of CKDStage GFR Description Management

I 90+Normal Renal Function(but urinalysis, structural abnormalities or genetic factors indicate renal disease)

Observation and control of blood pressure

II 60-89

Mildly reduced renal function(Stage 2 CKD should not be diagnosed on GFR alone - but urinalysis, structural abnormalities or genetic factors indicate renal disease)

Observation, control of blood pressure and cardiovascular risk factors

IIIa 45-59 Moderate decrease in renal function, with or without other evidence of kidney damage

Observation, control of blood pressure and cardiovascular risk factors

IIIb 30-44 Moderate decrease in renal function, with or without other evidence of kidney damage

Observation, control of blood pressure and cardiovascular risk factors

IV 15-29 Severely reduced renal function Planning for end stage renal failure

V <15 Very severe (end stage) renal failure Transplant or Dialysis

Renal profile in a 62 year-old man with type 2 diabetes2009 2010

Sodium 145 146 (135-145)Potassium 3.8 4.3 (3.5-5.1)Chloride 107 102 (95-110)Urea 5.6 9.0 (3.0-9.0)Creatinine 91 146 (60-130)eGFR 78 42 mL/min/1.73m2

A small risein creatinine Leads to a big

drop in GFR

Test your knowledge

• An 80 y.o. nursing home resident is admitted with respiratory tract infection. Her blood test results are:

• Sodium 157 (135–147 mmol/L)

• Urea 30 (2.5 – 6.6 mmol/L)

• Creatinine 150 (62 – 124 mol/L)

• Diagnosis: Dehydration

Imaging

• KUB (Kidney Urinary Bladder)

• IVP (Intravenous pyelography)

• Ultrasound

• CT scan (Computed tomography)

Plain X-ray (KUB)

• Kidneys overly the 12th ribs (renal angle)

• Difficult to visualise because of bowel gas.

• Can detect radio-opaque stone

IVP

• Multiple X-rays with contrast injection.

• Delineate structure and obstruction clearly.

• Note calyceal system and path of ureters.

(1) Right kidney (2) Left kidney (3) Minor calyx (4) Major calyx(5) Renal pelvis (6) Ureter

What is wrong with this KUBNormal KUB

What is wrong with the right IVP

Answer

• KUB• Bilateral staghorn

calculus (“deer horns”).

• Conform to the shapes of calyceal system.

• IVP• Rt hydronephrosis

• Rt ureter partially obstructed at level of L5

• Dilated balloon of Foley catheter in bladder

• “Missing” left kidney – nephrectomy, non-functioning

Ultrasound

• No radiation.• Delineate structure

clearly.• Detect mass lesions,

cysts and hydronephrosis.

• Measurement of kidney size.

CT scan

• Cross-sectional view of various slices of body.

• Delineate structure well.

• Require good knowledge of cross-sectional anatomy

A. external obliqueB. right costal carightilageC. rectus abdominusD. transverse colonE. transverse colonF. ascending colonG. pancreas - headH. duodenum - 2nd partI. renal veinJ. diaphragmK. psoas majorL. renal pyramid

http://iris3.med.tufts.edu/medgross/abl1.htm

Figure 1

Transpyloric plane cuts through the pylorus, the tips of the ninth costal cartilages and the lower border of the first lumbar vertebra.

• The transpyloric plane is clinically notable because it passes through several important abdominal structures. These include:

• the fundus of the gallbladder • the neck of the pancreas • the origins of the superior

mesenteric artery and portal vein • the hila of the kidneys • the root of the transverse

mesocolon • the duodenojejunal junction • the 2nd part of the duodenum • the termination of the spinal cord • the spleen

Polycystic kidneys

CT scanUltrasound

Renal biopsy

• Percutaneous needle biopsy from the lower pole.

• Establish diagnosis – adult nephrotic

• Determine prognosis – renal involvement in SLE

• Interpretation of renal pathology

http://www.niddk.nih.gov/health/kidney/pubs/kidney-biopsy/biopsy.htm

Renal biopsy specimen(a) Renal cortex, note the glomeruli, recognized as round red areas (wet preparation x10). (b) Renal medulla, reddish vasculature is present but no glomeruli seen (wet preparation x10)