Renal function tests

Dr Abeer Ahmed

Functions of the kidney

• Regulatory function• Excretion of waste products:• Endocrinal function• Metabolic Function

Nephron

• Functional unit of the kidney.

• Consists of:– Blood vessels:

– Urinary tubules:

• PCT.• LH.• DCT.• CD.

NEPHRON FUNCTIONS

• GLOMERULAR FILTRATION: glucose, amino acids, creatinine, urea, phosphates, uric acid

• TUBULAR REABSORPTION: bicarbonate, phosphates, sulfates, 65% of Na and water, glucose, K, amino acids, H ions

• TUBULAR SECRETION: hydrogen and potassium, remove acids (hydrogen) to maintain appropriate acid base balance, potassium,

Glomerular filtration• Of one-fifth of the cardiac output flows through the two kidneys

(i.e. a flow rate of 1000–1200 ml/min), the glomerulus filters 125-130 ml/min (GFR) of an essentially protein-free, cell-free fluid, called glomerular filtrate.

 • The rate of filtration across this membrane is governed by

multiple factors including renal blood flow and the integrity of the glomerulus membrane.

• Glomerulus has multiple small pores through which chemicals are filtered from the blood but excluding any substance with a molecular radius more than 4 nm (e.g. cellular blood component).

• Moreover, substances that are neutral or have positive charge are more likely to pass through the pores of the glomerulus than substances that are negatively charged (e.g. albumin).

Tubular reabsorption and secretion– The filtrate flows through the renal tubules, where water and

solutes may be reabsorbed, secreted, synthesized, or metabolized.

– Sodium is exchanged in the presence of the hormone aldosterone and water is exchanged in the presence of antidiuretic hormone (ADH).

– Exchange of solutes may occur as active transport, which occurs against the concentration gradient of the chemical and uses energy, or as passive transport, which occurs with the concentration gradient of the chemical.

Indications for RFT To asses the functional capacity of kidney To identify early renal impairment in patients at risk, such as

i. Diabetes mellitusii. Hypertension iii. SLEiv. UTIv. UT obstructionvi. Older age

To diagnose certain renal disorders To asses response to treatment in renal disorders To adjust dosage of chemotherapeutic drugs To plan renal replacement therapy in advanced renal diseases

Glomerular filtration Tests on glomerular permeability

Creatinine Creatinine (Mol. Wt. 113) is formed from breaking of 1-2% daily of

muscle creatine (relative to muscle mass). Freely filtered by the glomeruli.

– Not reabsorbed.– Conc inversely related to eGFR.– Low serum and urine creatinnie is found in children, females,

and elderly.– Small changes in creatinine within and around the reference

limits = large changes in GFR.– Increased conc occurred very late ( after GFR decrease about

50% of its normal value).– Normal values: (Female 0.6-1.1 mg/dl) (Male 0.9-1.3 mg/dl)– BUN/Creatinine ratio 10:1

BUN ( urea )• BUN results from catabolism of amino acids.• After filtration, about 50% is reabsorbed by the tubules.• Blood level is related to: renal function, Protein intake, and liver

function • Urea production is increased by a high protein intake , GIT

bleeding , Catabolic state and it is decreased in patients with a low protein intake or in patients with liver disease.

• Less useful than Creatinine better to be used with Cr• Sensitive but non-specific test• Reference Range of Serum or plasma BUN is: 8–20 mg/dL.• Reference Range of Blood urea = ( BUN X 2.14 ) is:

15–45 mg/dL.

Determination of Clearance Rate

Clearance = (U x V) / P U is the urinary concentration of creatinine (mg/dl) V is the 24-hours collected urine (L). P is the plasma concentration of creatinine (mg/dl)

Units = volume/unit time (mL/min)

Normal: Male: 97 to 137 ml/min. Female: 88 to 128 ml/min.

Glomerular Filtration Rate (GFR)

• Estimation of GFR is the Best single measure of assessment of renal function since its value is proportional to the number of intact nephrons.

• The GFR is the volume of fluid filtered from the glomeruli into Bowman's space per unit time.

• eGFR is more accurate than serum creatinine alone. Serum creatinine is affected by muscle mass, and related factors of age, sex, and race.

• Many methods are used to estimate the eGFR.

Estimated GFR ( eGFR)• Cockcroft - Gault equationCcr = (140 – age in yrs) x wt(kg) (0.85 in females) x Pcr 72MDRD ( modification of diet in renal disease)eGFR = 186 x {creatinine} - 1.154 ( age ) – 0.203 x 0.742 88.4

Renal Function Tests:• Serum BUN and creatinine ( convenient & insensitive )• Clearance rate (Creatinine )• eGFR• Full urine examination • Osmolarity measurement in plasma and urine• Water depriviation test• Acid load test• Urine analysis:specific proteinuria, glycosuria,aminoaciduria

RENAL FAILURE• Results when the kidneys cannot remove

the body’s metabolic wastes or perform their regulatory functions.

• The substances normally eliminated in the urine accumulate in the body fluids as a result of impaired renal excretion,

• leading to a disruption in endocrine and metabolic functions as well as fluid, electrolyte, and acid-base disturbances.

• It is a systemic disease and is a final common pathway of many different kidney and urinary tract diseases

Types

• Acute

• Chronic

Acute renal failure

• Sudden onset with oliguria/anuria

• Rapid rise in BUN and S Creatinine

Definition of CKD Structural or functional abnormalities of the

kidneys for >3 months, as manifested by Kidney damage, with or without decreased GFR, 2.

GFR <60 ml/min/1.73 m2, with or without kidney damage

The progressive, irreversible deterioration in renal function to maintain metabolic and fluid and electrolyte balance resulting in uremia and azotemia.

Stages of CRF

Stages of CRF: are based on the GFR. The normal GFR is 125cc/min/1.73m2

1. Stage 1 = GFR > 90 ml/min/1.73m2. Kidney damage with normal or increased GFR.

2. Stage 2 = GFR = 60-89 mL/min/1.73m2. Mild decrease in GFR.

3. Stage 3 = GFR = 30-59 mL/min/1.73m2. Moderate decrease in GFR.

4. Stage 4 = GFR = 15-29 mL/min/1.73m2. Severe decrease in GFR.

5. Stage 5 = GFR <15 mL/min/1.73 m2. Kidney failure

Chronic Renal Failure

Chronic Renal Failure

• Impaired homeostasis due to structural damage to kidney– Metabolic acidosis– Hypocalcemia– Hyperphosphatemia– Altered Vit D metabolism– Toxemia

Clinical Manifestations

1. CV manifestations:a. HPN – due to Na and H20 retention or from R-A-A activation,b. heart failure and edema - due to fluid overloadc. pericarditis - due to irritation of pericardial lining by uremic

toxins2. Dermatologic manifestations

a. severe pruritus is commonb. uremic frost, the deposit of urea crystals on the skin.

3. GI manifestations:a. anorexia, nausea and vomiting, and hiccupsb. The patient’s breath may have the odor of urine (uremic

fetor); this may be associated with inadequate dialysis4. Neurologic manifestations

a. altered LOC, inability to concentrate, muscle twitching, agitation, confusion and seizures.

b. Peripheral neuropathy, a disorder of the peripheral NS, is present in some patients

Acute renal failureChronic Renal failure

Historyrecent drug administration, toxin exposure,surgery/hypovolemia

polyuria, polydipsia

Urine outputoliguriapolyuria

Kidney sizenormal to largesmall

Anemiaabsentpresent

Metabolic bone disease

absentpresent