Renal Function Tests (Renal Parameters) Part 2
Sample
- The fresh serum is needed.
- Fresh urine is also needed.
To assess the renal function the following tests or parameters are advised.
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For concentration and Dilution advise Specific gravity (Sp.Gr).
- Specific gravity is the measure of the concentration of particles, including waste products and electrolytes in the urine.
- The definition of specific gravity is the weight of the urine compared to that distal water (water specific gravity is 1.000).
- Particles in the urine give it weight or Sp.Gr.
- Sp. Gr evaluate the concentrating and excretory power of the kidneys.
- The renal diseases will decrease the concentrating power, so leads to low Sp.Gr.
- When reporting Sp. Gr keep in mind the presence of glucose and proteinuria.
- An Overhydrated person will have diluted urine and low Sp.Gr.
- High specific gravity indicates concentrated urine and low specific gravity indicate diluted urine.
- To find the renal function as concentration and dilution:
- Concentration = Specific Gravity > 1.025
- Dilution = < 1.003
- Specific gravity is the measure of the concentration of particles, including waste products and electrolytes in the urine.
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Phenolsulfonphthalein (PSP) secretion test
- PSP is exogenous material given to the patient to assess the tubular excretory function of the kidney.
- This will reflect the renal plasma flow and tubular secretory function.
- It is injected into the patient and measured every 15 minutes.
- 94% of the PSP secreted with very little filtered by the glomeruli and it binds albumin in the blood.
- Normal
- > 25 % in urine in 15 minutes (25 to 50% PSP should be secreted in the urine in first 15 minutes)
- 10 to 15% additional secreted in the next 15 minutes.
- 55 to 75 % in 2 hours.
- PSP is exogenous material given to the patient to assess the tubular excretory function of the kidney.
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To measure glomerular filtration rate:
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- Glomerular filtration rate (GFR):
- This is the quantity of blood cleared of substances like creatinine and urea per unit time.
- It is the rate in milliliter (mL) per minute that substances like creatinine and urea filtered through the kidney glomeruli.
- Glomerular filtration rate (GFR):
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- GFR depends upon:
- Plasma concentration of the substance.
- The excretion rate of the kidney, this will reflect:
- Renal plasma flow.
- Glomerular filtration rate.
- The substance used should not be reabsorbed, secreted, synthesized, or degraded in the nephron.
- GFR is the most reliable measure of kidney function.
- GFR may be measured by giving exogenous substances like Inulin clearance.
- GFR may be measured by endogenous substances like creatinine and urea nitrogen.
- GFR depends upon:
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- Normal
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- Creatinine clearance
- Male = 97 to 137 ml / minute.
- Female = 88 to 128 mL / minute.
- Inulin clearance
- Male = 110 to 150 ml / minute.
- Female = 105 to 132 ml / minute.
- Urea clearance
- Maximum = 60 to 100 ml / minute.
- Creatinine clearance
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Serum Creatinine
- Creatinine is the end product of catabolism of creatine phosphate.
- Free creatinine is a waste product of creatine metabolism, is present in all body fluids and secretions.
- It is freely filtered by the glomerulus.
- There is diurnal variation when it is low at 7 AM and high at 7 PM.
- There is a slight increase after the meal and especially after the meat in the diet because a small amount is present in the meat.
- There is very little effect on liver function.
- This is the measure of kidney function.
- Normal 1.0 to 1.5 mg/dL
- Creatinine is the end product of catabolism of creatine phosphate.
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Creatinine clearance (GFR = Creatinine clearance)
- It estimates the renal excretion or filtering capacity of the kidney.
- Normal
- Male = 97 to 137 ml / minute
- Female = 88 to 128 ml / minute.
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Urine albumin
- Evaluation of the protein is a sensitive indicator of kidney function.
- Normally proteins are not present in the urine because the spaces in the glomerulus are too small to allow the protein to filter out.
- In the case of glomerulus membrane damage due to diseases, spaces become larger and allow the passage of protein in the urine.
- Protein (albumin) in the urine can be a sign of kidney disease.
- Proteinuria in pregnant women is an indicator of pre-eclampsia.
- Albumin levels can increase with heavy exercise, poor blood sugar control, urinary tract infections, and other illnesses.
- Normal
- In a 24-hour urine sample, the level is less than 30 mg/day.
- Normal
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Microalbuminuria
- This is an early sign of kidney disease, especially in people with diabetes.
- This is basically albumin in minute amount indicating glomerular membrane damage.
- Diabetic patients should have this test for microalbuminuria at least yearly.
- Normal
- Urine normally in healthy people contains from 30 mg/L to 300 mg/L of albumin.
- This is an early sign of kidney disease, especially in people with diabetes.
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Blood urea nitrogen (BUN)
- Blood Urea Nitrogen (BUN) is another measure of wastes (urea) in the blood.
- The BUN is used to measure whether a person is receiving the correct amount of dialysis.
- The normal BUN level:
- for a healthy adult is 7 to 20 mg/dL
- In children is 5 to 18 mg/dL.
- Patients on dialysis have higher BUN levels, usually 40 to 60 mg/dL.