Tests for Renal Function and Integrity (4th Year 2024, S) PDF

Institute of Infection, Veterinary and Ecological Sciences Acknowledgement to Dr Dan Batchelor! Thanks to Dr Dan Batchelor for sharing the previous teaching material! Tests for...

Institute of Infection, Veterinary and Ecological Sciences Acknowledgement to Dr Dan Batchelor! Thanks to Dr Dan Batchelor for sharing the previous teaching material! Tests for renal function and integrity Ioannis (Yannis) Oikonomidis DVM PhD DipACVP DipECVCP AFHEA MRCVS Senior Lecturer in Clinical Pathology [email protected]  Institute of Infection, Veterinary and Ecological Sciences Learning outcomes Outline the major kidney functions. List the tests recommended for assessing renal function. Explain purpose, interpretation, and limitations of different tests of renal function. Interpret azotemia in a clinical scenario. List other laboratory abnormalities that can be seen in kidney disease and explain the pathogenesis. Interpret urinalysis including USG, dipstick and sediment.  Institute of Infection, Veterinary and Ecological Sciences Kidney functions Control of body fluid balance Excretion of waste products Production of hormones (volume and composition) Maintenance of water, electrolyte and acid-base Erythropoietin balance Conservation of nutrients Calcitriol (active Vit D) Regulation of blood pressure Renin Update the blood every 30 minutes!  Institute of Infection, Veterinary and Ecological Sciences Renal function Nephron = the basic structural and functional unit of the kidney ✓Glomerulus, Bowman’s capsule, tubules, collecting duct, blood vessels/capillaries Conserve Excrete ▪ Water ▪ Urea ▪ Glucose ▪ Creatinine ▪ Amino acids/proteins ▪ PO4 ▪ Na+ ▪ K+ ▪ Cl- ▪ H+ ▪ HCO3- ▪ NH4+ ▪ Ca2+ ▪ Lactate and ketones ▪ Mg2+ ▪ Bilirubin  Institute of Infection, Veterinary and Ecological Sciences Tests for renal function Blood tests Urinalysis ✓Biochemistry ✓USG, dipstick, sediment o Nitrogenous wastes (urea, creatinine) ✓UPCR o Electrolytes and minerals (Na+, Cl-, K+, Ca2+, PO ) ✓Fractional excretion of electrolytes 4 ✓Haematology ✓Blood gas analysis  Institute of Infection, Veterinary and Ecological Sciences Glomerular filtration rate (GFR) Inulin clearance Urea Creatinine The rate fluid moves from plasma to Direct measurement Indirect estimation glomerular filtrate  Institute of Infection, Veterinary and Ecological Sciences Urea - physiology Synthesis occurs in hepatocytes via the urea cycle, which eliminates excess NH4+ formed in tissues. Passes freely across the glomerular filtration barrier. Half of it is reabsorbed in proximal and collecting tubules and the rest is excreted. A small proportion also excreted in faeces.  Institute of Infection, Veterinary and Ecological Sciences Urea - pathology Decreased excretion Decreased synthesis ✓Prerenal, renal, postrenal ✓Liver insufficiency or PSS azotaemia ✓Decreased protein intake Increased production ✓Urea cycle enzyme deficiencies ✓Intestinal haemorrhage Increased excretion ✓Increased proteolysis mild ✓Any cause of polyuria ✓Increased protein intake  Institute of Infection, Veterinary and Ecological Sciences Creatinine - physiology Produced constantly from creatine degradation in muscles Passes freely across the glomerular filtration barrier. It is not reabsorbed, but might be excreted by proximal tubules. Excretion in faeces?  Institute of Infection, Veterinary and Ecological Sciences Creatinine - pathology Decreased excretion ✓Prerenal, renal, postrenal Decreased production conditions ✓Reduced muscle mass Increased production ✓High muscle mass mild ✓Increased protein intake Measure both, but creatinine more reliable!  Institute of Infection, Veterinary and Ecological Sciences Azotaemia Increase in nonprotein nitrogenous compounds in the blood → routinely detected as increased serum urea and/or creatinine concentration Prerenal Acute Azotaemia Renal Chronic Postrenal  Institute of Infection, Veterinary and Ecological Sciences Prerenal azotaemia Aka volume- Due to reduced Clinical signs of Appropriately Response to fluid responsive or renal blood flow dehydration concentrated therapy transient Hypovolaemia or and/or urine azotaemia decreased cardiac hypovolaemia USG>1.030 in output → Often ↑urea > dogs decreased GFR → ↑creatinine USG>1.035 in cats decreased clearance Increased reabsorption of urea (ADH effect)  Institute of Infection, Veterinary and Ecological Sciences Renal azotaemia Due to kidney disease Loss of ≈75% of nephron Inadequately concentrated See lectures next week! functional capacity to reduce urine GFR sufficiently to produce USG0.4  Institute of Infection, Veterinary and Ecological Sciences Renal proteinuria 15 Proteinuria should be checked for: Location Persistence Magnitude (UPCR) >2.0 – Suggestive of glomerulopathy Glomerular problem Typical treatment thresholds: 2.0 Dogs >0.5 Cats >0.4 0.4-0.5 0.2 UPCR Tubulointerstitial Normal problem  Institute of Infection, Veterinary and Ecological Sciences Glucose in urine (glucosuria) Relatively small molecule (Mr=180) that passes freely through the glomerular filtration barrier Reabsorbed in the proximal tubules via a Na+-glucose cotransporter system → not normally present in urine Hyperglycaemic glucosuria Serum GLU >10 mmol/l in dogs and >13-16 mmol/l in cats Renal glucosuria Defective reabsorption by damaged/abnormal proximal tubules Fanconi syndrome, proximal tubular toxicosis or ischaemia  Institute of Infection, Veterinary and Ecological Sciences Haem (blood) in urine Detects haem-containing compounds, such as haemoglobin or myoglobin Not normally present in urine Haematuria Haemorrhage into the urogenital tract (could be iatrogenic if cystocentesis) Haemoglobinuria Intravascular haemolysis (also concurrent haemoglobinaemia) or in vitro haemolysis Myoglobinuria Myocyte damage or necrosis  Institute of Infection, Veterinary and Ecological Sciences Urine sediment examination Typically 5 ml of urine are used. Wet (unstained) and stained preparations  Institute of Infection, Veterinary and Ecological Sciences Erythrocytes in urine sediment (haematuria) May be found in low Pathological Iatrogenic Oestrus numbers haemorrhage haemorrhage From genital (