2. CONCENTRATION & DILUTION TESTS Aim-To evaluate functional capacity of renal tubules Ability of nephron to do so dependent upon Functional activity of tubular cells in renal medulla & Presence of ADH Failure to achieve adequate urinery concentration due to Defects in renal medulla [NDI] Lack of ADH [CDI ] Traditionally concentration is determined by Specific gravity of urine gives rough estimate of osmolarityWATER DEPRIVATION OR CONCENTRATION TEST To diagnose tubular disease in early stage Artificial fluid deprivation for > 14 hrs No food or water after 6 p.m on the night preceding the test. Discard any urine voided during the night & the first specimen- voided at 7.00 a.m A second specimen at 8 a.m & tested If the nephron is normal ,water is selectively reabsorbed & excretion of urine of high solute concentration [SG-1.025 or more] with an osmolality exceeds 850 mOsm/kg If tubular cells are non functional solute concentration remains constant regardless of stress of water deprivation The test should not be performed on a dehydrated patientVASOPRESSIN TEST Depends only on renal tubular function At 8 pm-five units of vasopressin tannate is injected subcutaneously All urine samples are collected separately until 9 a.m. the next morning Satisfactory concentration is shown by at least one sample having a specific gravity above 1.020, or an osmolality above 800 m osm/kg This test will often detect impaired function when creatinine clearance is normal, as in hypertension or potassium deficiencyDILUTION TEST/WATER EXCESS TESTS After an overnight fast the patient empties his bladder completely and is given 1000 ml of water to drink Urine specimens are collected for the next 4 hours, the patient emptying bladder completely on each occasion Unless there is renal functional impairment, the patient will excrete at least 700 ml of urine in the 4 hours, and at least one specimen will have a specific gravity less than 1.004. Kidneys which are severely damaged cannot excrete a urine of lower specific gravity than 1.010 or a volume above 400 ml in this time. There is a delayed diuresis Abnormal results are also found if there is delayed water absorption or adrenal cortical hypofunction If renal tubules are diseased the concentration of solutes in the urine remain constant irrespective of excess water intake The test should not be done if there is oedema or renal failure; water intoxication may resultDYE EXCRETION TESTS Using Phenolsulphonphthalein (phenol red) or Indigo-carmine Its excretion essentially tests for renal plasma flow and is therefore impaired early in conditions such as heart failure[3] BLOOD CHEMISTRYImpairment of renal function leads to elevation of end products of protein metabolism thus increased accumulation of urea, BUN, & creatinine in blood & azotemia resultsUrea End-product of protein metabolism chiefly excreted through the kidney It is filtered by the glomeruli and variably reabsorbed in the tubules The normal plasma concentration is 20-40 mg/dl Blood urea concentration is about 14% less than plasma concentration. Blood urea does not rise until a reduction of 50-60% of GFR The real urea concentration is BUN x 2.14 Raised -High-protein diet , Hypercatabolic states, Surgery, Infection ,Trauma , Steroid therapy , Tetracyclines , Hypotension, dehydration Low - Low-protein diet , Old age (reduced catabolism]BUN [blood urea nitrogen] Normal BUN range is 8-25 mg/dL It is not possible to detect renal damage by a raised BUN until renal function has fallen by about 50 percent as measured by the creatinine clearance test Estimation is most useful for the assessment of the severity and progress of renal failure in Acute tubular necrosis, Acute glomerulonephritis, Chronic renal disease, Post-renal obstruction Decreased BUN -in Low protein diet,Liver damage,DialysisCreatinine The breakdown product of creatine phosphate released from skeletal muscle at a steady rate. It is filtered by the glomerulus. It is generally a more sensitive and specific test for renal function than the BUN. Normal range is 0.6-1.3mg/dL High levels of creatinine associated with high levels of beta 2 microblobulin in the serum as well as urine Increased-Impaired renal function,Very high protein diet, Anabolic steroid users, Vary large muscle mass: body builders, giants, acromegaly ,Rhabdomyolysis/crush injury.Athletes taking oral creatine drugsUric Acid Metabolite of purine metabolism Filtered by the glomeruli and both reabsorbed and secreted by the renal tubules. Normal value-2.4-7.0 mg/dl Increased -Renal failure,Gout,Liver and sweetbread gourmets,Lead poisoning,Thiazide diuretics High dose aspirin, Burns, Crush injuries, Severe hemolytic anemia, Myeloproliferative disorders Plasma cell myeloma, Tumor lysis: post chemotherapyBUN/creatinine ratio Of > 15 is abnormal and indicates pre or post renal azotaemia It is also elevated in all conditions associated with urea overproduction. A low ratio is found in pregnancy, overhydration, severe liver disease, and malnutrition. The ratio is normal in renal azotaemia