Renal Functions

Sample for Renal Function Tests

1. A fresh serum is needed.
2. Fresh urine is also needed.

To assess renal function, the following tests or parameters are advised.

• For concentration and Dilution, advise Specific gravity (Sp. Gr).

Specific gravity

1. It is the measure of the concentration of particles, including waste products and electrolytes, in the urine.
   1. The definition of specific gravity is the weight of the urine compared to that of distal water (water-specific gravity is 1.000).
   2. Particles in the urine give it weight or Sp.Gr.
   3. Specific Gravity evaluates the concentrating and excretory power of the kidneys.
   4. The renal diseases will decrease the concentrating power, so leads to low Sp.Gr.

1. 1. When reporting Sp. Gr keep in mind the presence of glucose and proteinuria.
   2. An Overhydrated person will have diluted urine and low Sp.Gr.
   3. High specific gravity indicates concentrated urine, and low specific gravity indicates diluted urine.
2. To find the renal function as concentration and dilution:
   1. Concentration = Specific Gravity > 1.025
   2. Dilution = < 1.003

Phenolsulfonphthalein (PSP) secretion test

1. PSP is exogenous material given to the patient to assess the tubular excretory function of the kidney.
   1. This will reflect the renal plasma flow and tubular secretory function.
2. It is injected into the patient and measured every 15 minutes.
3. 94% of the PSP is secreted with very little filtered by the glomeruli, and it binds albumin in the blood.
4. This test PSP is difficult; now, p-aminohippuric acid is used to find tubular secretion and renal blood flow.
5. Normal
   1. >25 % in urine in 15 minutes (25% to 50% PSP should be secreted in the urine  in the first 15 minutes)
   2. 10% to 15% additional secreted in the next 15 minutes.
   3. 55% to 75 % in 2 hours.

Glomerular filtration rate:

Definition of Glomerular filtration rate (GFR):

1. This is the quantity of blood cleared of substances like creatinine and urea per unit of time.
2. Substances like creatinine and urea filter through the kidney glomeruli at the rate of milliliters (mL) per minute.

3. GFR depends upon the following:
   3. 1. Plasma concentration of the substance.
      2. The excretion rate of the kidney will reflect the following:
         1. Renal plasma flow.
         2. Glomerular filtration rate.
      3. The substance used should not be reabsorbed, secreted, synthesized, or degraded in the nephron.
   4. GFR is the most reliable measure of kidney function.
      1. GFR may be measured by giving exogenous substances like Inulin clearance.
      2. GFR may be measured by endogenous substances like creatinine and urea nitrogen.
4. Normal GFR
   1. Creatinine clearance
      1. Male = 97 to 137 ml/minute.
      2. Female = 88 to 128 mL/minute.
   2. Inulin clearance
      1. Male = 110 to 150 ml / minute.
      2. Female = 105 to 132 ml/minute.
   3. Urea clearance
      1. Maximum = 60 to 100 ml/minute.

Serum Creatinine

1. Creatinine is the end product of the catabolism of creatine phosphate.
   1. Free creatinine, a waste product of creatine metabolism, is present in all body fluids and secretions.
   2. It is freely filtered by the glomerulus.
   3. There is diurnal variation when it is low at 7 AM and high at 7 PM.
   4. 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.
   5. There is very little effect on liver function.
   6. This is the measure of kidney function.
2. Normal serum creatinine = 1.0 to 1.5 mg/dL

Creatinine clearance (GFR = Creatinine clearance)

1. It estimates the renal excretion or filtering capacity of the kidney.
2. Normal creatinine clearance
   1.  Male = 97 to 137 ml/minute
   2. Female = 88 to 128 ml/minute.

Urine albumin

1. Evaluation of the protein is a sensitive indicator of kidney function.
2. Normally proteins are not present in the urine because the spaces in the glomerulus are too small to allow the protein to filter out.
   1. In the case of glomerulus membrane damage due to diseases, spaces become larger and allow the passage of protein in the urine.
3. Protein (albumin) in the urine can be a sign of kidney disease.
   1. Proteinuria in pregnant women is an indicator of pre-eclampsia.
4. Albumin levels can increase with heavy exercise, poor blood sugar control, urinary tract infections, and other illnesses.
5. Normal urine albumin
   1. The level in a 24-hour urine sample is less than 30 mg/day.

Microalbuminuria

1. This is an early sign of kidney disease, especially in people with diabetes.
   1. This is basically albumin in minute amounts indicating glomerular membrane damage.
2. Diabetic patients should have this test for microalbuminuria at least yearly.
3. Normal microalbuminuria
   1. Urine normally in healthy people contains from 30 mg/L to 300 mg/L of albumin.

Blood urea nitrogen (BUN)

1. Blood Urea Nitrogen (BUN) is another measure of waste (urea) in the blood.
2. BUN is used to measure whether a person is receiving the correct amount of dialysis.
3. The normal BUN level:
   1. For a healthy adult is 7 to 20 mg/dL
   2. In children is 5 to 18 mg/dL.
   3. Patients on dialysis have higher BUN levels, usually 40 to 60 mg/dL.