Renal Function Tests

Functions of Kidney

The kidney has five major functions

Ø Removal of waste products/ toxic substances

Ø Regulation of water and electrolyte balance

Ø Regulation of acid-base homeostasis

Ø Conservation of Protein

Ø Endocrine functions

n Erythropoietin production

n Renin - angiotensin production

n Calcitriol- Vitamin D metabolism

Why Test Renal Function?

n To identify renal dysfunction.

n To diagnose renal disease.

n To reveal the principle site of pathology

n To assess the degree of functional damage

n To monitor disease progress.

n To monitor response to treatment.

Clinical history

Ø History of renal disease

Ø Evidence of systemic illness

Ø Family history of renal disease

Ø Medications being taken

Signs and Symptoms of Renal Diseases

n Symptoms of Uraemia (nausea, vomiting, lethargy)

n Disorders of Urine volume (polyuria, anuria)

n Alterations in urine composition (haematuria, proteinuria)

n Pain ( calculi)

n Oedema (hypoalbuminaemia, water retention)

n Disorders of Micturation (frequency, nocturia, retention, dysuria)

Biochemical Tests of Renal Function

n Urinalysis

n Appearance

n Specific gravity and osmolality

n pH

n Glucose

n Protein

n Urinary sediments

n Measurement of GFR

n Creatinine clearance tests

n Serum Creatinine/Urea

n Cystatin C

n Tubular function tests

Urine Routine Examination

n Appearance

n Urine volume (750-2500 ml/24h)

n Anuria: 100 ml/24 h

n Oliguria: 400 ml/24 h

n Polyuria: >3000 ml/24 h

n Specific gravity (1005-1020)

n Increased: Pre renal uraemia

n Decreased: Diabetes insipidus

n Fixed specific gravity e.g. CRF (1010)

n pH (5.5-8.0) - reflects acid base status

n Protein

n Glucose

n Formed elements

n Casts

n Crystals

24 hour urine protein excretion

v > 150mg/24 hour = proteinuria

v Gives a more accurate assessment of the severity of the proteinuria

v > 3.5 g/24 hour (with associated features) = nephrotic syndrome

Classification of Proteinuria

n Tubular proteinuria

n Tubular dysfunction

n Overflow proteinuria

n Glomerular proteinuria

n Selective proteinuria

n Non-selective proteinuria

n microalbuminuria

Urine microscopy

n To look for casts, white cells and red cells may give a clue to the diagnosis of:

n glomerulonephritis

n pyelonephritis

n tubular damage

Serum Creatinine

n Reliable test for glomerular function

n Production determined by muscle mass which is related to age, sex and weight.

n Reference range- 70-133 umol/l

n Mild renal damage: <200 umol/l

n Moderate renal damage: 200-400 umol/l

n Severe renal damage: > 400 umol/l

Creatinine Clearance

n Most sensitive test for renal function

n The volume of blood from which creatinine is completely removed per unit time

n Clearance = (U x V)/P

n U is urinary concentration of creatinine

n V is the rate of urine formation (mL/min)

n P is the plasma concentration of creatinine

n Units = volume/unit time (mL/min)

n Cockcoft - Gault Formula*

CC = k[(140-Age) x weight (Kg))] / Creatinine (µmol/L)

k = 0.81 for males & 0.85 for females

n Creatinine clearance = U x V

______ = mL / minute

P x 24 x 60

Indications

1. 1. Assessment of potential kidney donor
   2. Investigation of patient with abnormal renal function
   3. Patient on toxic drugs,which are excreted by kidneys

Precautions

1. 1. Take 3-4 L container
   2. Void all the urine in the container
   3. Avoid red-meat

Urea

n Urea is synthesized in liver as a by –product of deamination of amino acids – Urea cycle

n Serum urea concentration is used for assessment of renal function

n Reference Range 2.5-6.7 mmol /L

Plasma Electrolytes

n Plasma Sodium (135-148 mmol/l)

n Early CRF - Normal

n ARF /Late CRF - Hyponatraemia

n Plasma potassium (3.5-5.0 mmol/l)

n Early CRF : Normokalaemia

n ARF /Late CRF : Hyperkalaemia

n Plasma Bicarbonate (22-28 mmol/l)

n ARF / CRF : Low due to metabolic acidosis

n Serum chloride (95-107 mmol/l)

n Early CRF: Increased

n Anion gap

n (Na +K) - (CI + HCO3) = upto 16 mmol/l

n Normal anion gap: early CRF

n High anion gap: Late CRF

n Serum calcium (2.05-2.55mmol/l)

n Reduced in RF

n Serum phosphate (0.8-1.45mmol/l)

n Increased in RF

n Serum Magnesium ( 1mmol/l)

n Increased in RF

ARF : Prerenal : Renal

n Urine sodium (spot)

n Helpful in D/D of oliguria

n PRU: Urine sodium < 20 mmol/l

n ATN: Urine sodium > 40 mmol/l

n Renal fractional excretion of sodium

n FE Na < 1%: PRU

n FE Na > 1%: ATN, Obstructive nephropathy, CRF

n Urine : plasma osmolality

n PRU > 1.5 : 1

n ATN < 1.1 : 1

n CRF 1 : 1

Other tests

n Blood Complete and E.S.R

n Anaemia

n Abnormal T.L.C and D.L.C

n Plasma and urine electrophoresis if suspect multiple myeloma with Bence Jones proteinuria

n Urine for myoglobin / haemoglobin

n Renal biopsy if suspect glomerular disease

n HbA1c to assess diabetic control

n Renal ultrasound if suspect renal disease

n Plain and contrast X-ray

n C.T and M.R.I