BMED12-118 Laboratory Medicine - Week 5 - Renal Disease & UTI PDF

BMED12-118 LABORATORY MEDICINE ​John Leggett ​[email protected] Week 5: Investigating Renal Disease At the end of this week students should be able to: Describe the main pathology tests used to investigate kidney function and damage Understand how kidney diseases can affect these tests...

BMED12-118 LABORATORY MEDICINE ​John Leggett ​[email protected] Week 5: Investigating Renal Disease At the end of this week students should be able to: Describe the main pathology tests used to investigate kidney function and damage Understand how kidney diseases can affect these tests Discuss the causes of glomerulonephritis and the tests used to investigate this disease Describe the laboratory main findings in pyelonephritis and cystitis and how they can be differentiated Understand the pathogenesis of nephrosclerosis Explain the kidney changes occurring in early and late stage diabetic nephropathy. The Kidney ​Functions ​Excretes waste products of metabolism ​ ​ echanisms M Glomerular Filtration ​Regulates the body’s water, electrolytes ​ Tubular Absorption ​Maintains acid-base balance of plasma ​ Tubular Secretion ​Secretes hormones | 3 The Glomerulus ​Network of capillaries ​Fenestrated endothelium surrounded by a glomerular basement membrane. ​Two layers of epithelial cells create the Bowmans space which collects the filtrate ​Supportive mesangial cells Selectively permeably to water and small solutes. Impermeable to albumin and larger molecules. | 4 The Glomerulus ​GFR regulated by 1. Autoregulation 2. Tubuloglomerular feedback 3. Neurohomronal influences The Juxtaglomerular Apparatus (JGA) & Macula Densa (MD) involved 1&2 MD sensesCl- in tubular fluid. Low GFR means low tubular Cl-. Response is to dilate afferent arteriole & constrict efferent to up pressure and restore GFR. Neurohormonal influences in patient with systemic hypotension due to heart failure, or fluid depletion due to gastro. | 5 Involves angiotensin II & | 6 Acid – Base Balance ​Daily metabolism produces acid in the body. ​This acid is buffered using bicarbonate to maintain normal blood pH. ​The kidneys excrete acid and reabsorb/produce bicarbonate equalising the effects of daily metabolism and producing acidic urine. ​Kidney disease can result in a reduced ability to secrete acid and/or reabsorb/produce bicarbonate and can lead to acidosis (decrease blood pH). | 7 Classification of ​The easiest way to classify kidney diseases is based on the four morphologic components of the Renal Diseases kidney. Glomerular disease – network of vessels which serves as the first filter of blood in the kidney. Tubular disease – the main function of the tubules is to regulate water and solute reabsorption/secretion. Interstitium disease – tissue surrounding the loop of Henle (main functions are water reabsorption) Blood vessel disease – disorders of the blood vessels affect the areas supplied by the vessels ​Some diseases affect more than one area. ​The functional interdependence of the kidney structures also means that damage to one area will eventually affect one or more of the other areas. ​End stage kidney disease (all four areas are | 8 Manifestations of ​Azotemia – elevated serum urea and creatinine Kidney Diseases ​Haematuria/Proteinuria – blood/protein in the urine ​Nephritic Syndrome – generally due to inflammation of the glomerulus and presents with haematuria, reduced GFR and mild proteinuria ​Nephrotic Syndrome – Due to changes to capillary walls in glomerulus causing increased permeability to plasma proteins. Presents with heavy proteinuria, hypoalbuminemia, severe oedema ​Tubular Defects – polyuria (excessive urine formation), nocturia and electrolyte disorders ​Chronic Kidney Disease – the presence of diminished GFR for at least 3 months due to any cause | 9 ​End Stage Renal Disease – when GFR drops Investigating Kidney Disease ​Creatinine (serum) ​Produced by muscle, excreted by the kidney. Serum levels are a good indicator of kidney function. High levels in the blood indicate reduced kidney function, particularly decreased glomerular filtration rate. ​(urine) ​Because creatinine is released in urine at a constant rate, its level in urine is a good indicator of the concentration of urine (how dilute it is). This is usually used as a marker to normalise the levels other urinary analytes. ​The creatinine assay involves using a reagent that reacts in the presence of creatinine to produce a coloured product that can be measured by spectrophotometry. | 10 Investigating Kidney Disease ​Estimated Glomerular filtration Rate (eGFR) ​This is a measure of how much blood is getting filtered by the kidney (calculated using the Cockcroft and Gault formula from serum creatinine values). ​It is a measure of overall kidney function. ​Reduced renal filtration can be pre-renal (artery stenosis), renal (glomerular diseases, or tubule diseases) or post-renal (obstruction). ​Cockcroft and Gault formula (don’t need to memorise) = Creatinine clearance (mL/min) ​Males = (140-age) x weight (kg) / 0.814 x plasma creatinine (umol/L) ​Females = 0.85 x (140-age) x weight (kg) / 0.814 x plasma creatinine (umol/L) ​Normal > 70 mL/min in a young adult. Typically falling approx 0.5 mL/min per year at ages over 30 years. ​Usually use an automated calculator such as: http://egfrcalc.renal.org/. | 11 Investigating Kidney Disease ​Urea (serum) (spectrophotometry) ​Urea is produced in the liver (ammonia produced during amino acid metabolism is converted to urea in the liver) and excreted in urine by the kidneys (enters filtrate as well as actively secreted). Increased serum urea is seen in kidney disease. Low levels generally indicate liver disease. ​Albumin/Protein (urine/serum) (spectrophotometry) ​Increased albumin (or total protein) in the urine is a sign of glomerular damage. Usually the amount of albumin is expressed as a ratio with the amount of creatinine in the urine. ​Serum albumin or total protein may be decreased in kidney disease due to loss into the urine. | 12 Investigating Kidney ​Cells in the urine (microscopy) Disease ​Red or white blood cells in the urine (haematuria/pyuria) is often a symptom of kidney disease. ​ asts (cylindrical accumulations of cells) in urine C indicate a renal origin as casts are formed in the tubules. ​Dysmorphic red blood cells are seen from glomerular origin as they are squeezed through the basement membrane. | 13  Referenc Ion e selective electrode electrode Investigating Kidney Disease Measures the potential (charge) difference between the two electrodes created by the Ion ​Serum Electrolytes movement of a selective ​[ion selective electrodes] specific ion membrane Potassium Increased K+ is commonly found in kidney failure (decreased secretion) Sodium Increased serum Na+ is indicative of aldosteronism. Reduced levels can sometimes occur in kidney failure. Chloride Decreased Cl- may be seen in diseases affecting the kidney tubules. Bicarbonate ​Low levels of bicarbonate can be seen in kidney disease due to a reduced reabsorptive capacity (metabolic acidosis) ​ | 14 Glomerulonephritis  ​Inflammation of the glomerulus. Glomerulonephritis ​Many causes from infection to autoimmune. ​Immune mediated injury is involved in many forms of glomerulonephritis. ​Anitbody-antigen complexes deposit or form in the glomerulus elicit a local inflammatory response that produces injury. ​Circulating immune complex deposits ​Post infection (streptococcus, hepatitis B/C) ​Tumour antigens ​Systemic lupus erythematosus ​In-situ immune complex formation (autoimmune) ​Anti-glomerular basement membrane disease - self reactive (auto) antibodies directed against GBM antigens bind the GMB and causes inflammation. ​Membranous nephrophathy (antibodies against epithelial cells) | 16 Glomerulonephritis ​Injury occurs due to: complement activation leukocyte migration neutrophils and macrophages can cause oxidative damage to the local environment Release of cytokines and growth factors can cause injury and proliferation of the glomerular cells. ​- sclerosis and thickening of the glomerulus (reduced GFR) ​- necrosis and loss of cells (loss of function, changes filtration) ​Can present with nephritic or nephrotic syndrome ​Nephritic ​Haematuria ​Red cell casts (or dysmorphic RBCs ) in urine ​Uraemia ​Reduced GFR ​Nephrotic ​Proteinuria | 17 ​Oedema Glomerulonephritis ​Diagnosis: ​Reduced GFR, increased urinary protein/albumin or urea ​Complement levels ​Bacterial or viral antigens ​Autoantibodies (against nuclear or glomerular antigens) ​Differentiation between SLE and anti-GBM disease can be done using biopsy and immunofluorescence. Granular pattern of immunofluorescence (D) is characteristic of circulating immune complexes gathering in the glomerulus (SLE) Linear pattern E is characteristic of direct antibody binding to GBM antigens (anti-GBM disease) | 18 Pyelonephritis/ Cystitis/ UTI Terminology ​Pyelonephritis = kidney inflammation ​Cystitis = bladder inflammation ​Usually due to infection ​Urinary tract infection (UTI) = an infection in the urinary tract (kidney, ureters, bladder) | 20 Pyelonephritis ​Inflammation of the kidney (affecting the tubules, interstitium and renal pelvis). ​One of the most common kidney diseases. ​Can be acute or chronic. ​Bacterial infection is generally the cause and is associated with bladder infections (cystitis). ​85% of UTIs are caused by normal flora of the intestinal tract such as E. coli and Enterobacter that enter via the urethra. These bacteria enter the bladder and can ascend to the kidneys. Rarely do bacteria enter the kidneys via the bloodstream. ​Symptoms include: ​Sudden pain in the abdomen or back/flank ​Painful urination, frequency and urgency. ​Fever | 21 Diagnosis ​Haematuria: blood in the urine can often occur due to UTI. The presence of casts suggests pyelonephritis as they are only formed in the tubules. ​Pyuria (leukocytes in urine). The presence of casts indicates pyelonephritis. ​Bacteruria: a pure (single) culture indicates infection. Mixed culture suggests contamination. ​Diagnosis of infection is done by urine culture. ​Treatment decisions made using antibiotic sensitivity tests | 22 Nephrosclerosis Nephrosclerosis ​Nephrosclerosis is sclerosis (stiffening) of the renal arterioles and small arteries. It is one of the most common causes of end stage renal disease. ​Vessels have thickened walls and narrowed lumens resulting in reduced perfusion of the underlying tissue. ​The initiating event appears to be vascular injury generally due to hypertension. This injury leads to inflammation in the area causing cell proliferation and deposition of extra cellular matrix. ​ he consequent reduction in blood flow can lead T to glomerular, tubular and interstitial injury that results in atrophy, fibrosis (granulated surface) and reduction in organ size. ​In more serious cases further vascular injury can lead to atherosclerotic plaque formation and/or thrombus formation which can result in severe ischemia. ​Any area of the kidney can be affected and therefore the diagnosis of nephrosclerosis can be difficult. | 24 Renal Artery ​Renal artery stenosis is characterised by narrowing of the renal artery by an atheromatous Stenosis plaque. ​Initiation is by vessel injury (due to dyslipidemia, inflammation, smoking, diabetes or hypertension). ​Vascular permeability increases resulting in fat accumulation. ​Endothelial and smooth muscle cells proliferate. ​Macrophages enter and cause further inflammation. ​As the renal artery lumen progressively narrows, renal blood flow decreases. Eventually, the decreased perfusion compromises renal function and structure. ​The main problem is that the juxtaglomerular cells sense the reduced blood flow and misinterprets this information as low blood pressure producing renin in response. This stimulates the production of angiotensin II and an increase in sodium and water retention to increase blood pressure. ​The ischemic kidney undergoes changes such as atrophy, fibrosis, glomerular changes. | 25 ​GFR will eventually decrease and proteinuria may Diabetic Nephropathy Diabetic ​Nephropathy = kidney disease Nephropathy ​Diabetic nephropathy = kidney damage due to diabetes. ​Approximately 40% of people with diabetes will develop kidney disease. ​It is the leading cause of chronic kidney failure in the USA. ​Due to damage of blood vessels by hyperglycemia. Three changes occur: ​1) Capillary basement membrane thickening in the glomerulus and eventually the tubules. This can lead to scarring. The glomerulus can become leaky and the tubules secretory and absorption functions can be compromised. ​2) Renal atherosclerosis: renal vascular insufficiency ​3) Inflammation generally affects the tubules. | 27 Mechanism ​Long term hyperglycemia has several effects thought to contribute to nephropathy: ​Glucose forms “advanced glycation end products” (AGEs) with amino acids of intracellular and extracellular proteins. High blood glucose levels greatly increases AGE formation. These AGE molecules can: ​- stimulate the release of cytokines and growth factors that can cause inflammation and vascular changes (vascular endothelial growth factor VEGF) ​- generate reactive oxygen species in endothelial cells increasing the risk of vascular inflammation ​- enhances proliferation of vascular smooth muscle and extracellular matrix. ​- cross link collagen fibres in blood vessels causing them to lose elasticity ​- cause proteins to become trapped in blood vessels such as LDL and albumin ​The end result being a state of inflammation in blood vessels leading to thickening, damage, | 28 plaque formation, narrowing. For the kidney this Diagnosis ​Earliest sign is micro albuminuria. ​Two raised urine albumin tests 3-6 months apart Tubules in a diabetic person is generally diagnostic of diabetic nephropathy. ​Creatinine tests will be done to determine the extent of damage. ​There is no treatment for early kidney damage but attempts to control blood sugar and blood pressure are made. While urine albumin and serum creatinine will be performed regularly. ​A kidney biopsy may be performed to confirm the diagnosis in later stage disease. This would show thickening of the tubule basement membrane and nodular sclerosis in the glomerulus due to inflammation. | 29  Kidney function can be assessed using various Summary tests: Creatinine eGFR Urinary protein, albumin Serum urea & electrolytes Cells in the urine Glomerulonephritis is often immune mediated and diagnosis involves a combination of many investigations. UTIs can be differentiated as pyelonephritis or cystitis mainly on the basis of the presence/absence of casts in the urine. Nephrosclerosis can be triggered by vascular injury due to hypertension, smoking, diabetes. Kidney function tests will often be impaired but imaging is usually required for diagnosis. | 30 Diabetic nephropathy is the leading cause of Additional Reading ​Kidney diseases ​Chapter 20 of the Text Book (Pathological Basis of Disease) ​Diabetic Nephropathy ​Pages 1115-1119 of the Text Book (Pathological Basis of Disease) ​ ​RCPA manual ​https://www.rcpa.edu.au/Library/Practising-Patholo gy/RCPA-Manual/Items/Pathology-Tests/C/Creatinin e ​https://www.rcpa.edu.au/Library/Practising-Patholo gy/RCPA-Manual/Items/Clinical-Problems/D/Diabet es-mellitus ​https://www.rcpa.edu.au/Library/Practising-Patholo | 31 gy/RCPA-Manual/Items/Pathology-Tests/M/MCS-urin Revision Questions 1) What are the four areas of the kidney that can be affected in kidney disease? 2) What are the main laboratory tests used to investigate kidney disease? 3) Which substances would typically increase in the blood in kidney disease? 4) Which substances could typically appear in urine in kidney disease? 5) What serum test is used to calculate the glomerular filtration rate? 6) Explain what casts are and where they are formed? 7) If a patient had hematuria from a suspected glomerular cause, what two features of RBCs would you expect to see in their urine? 8) In most cases of infective pyelonephritis, how would the bacteria have reached the kidney? 9) List three typical symptoms of pyelonephritis. 10) How could you tell if a urine sample was from a patient with a cystitis or pyelonephritis? 11) What is the typical pathology finding in early stage diabetic nephropathy? 12) What are the typical features of the nephron in late stage diabetic nephropathy? | 32