Creatinine Clearance Test to Estimate Renal Function
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Kidney is a part of group of organs that constitute the urinary tract system which consists of two kidneys, two ureters, bladder and urethra. The kidneys do the major function of the urinary system. The other parts of the system are mainly passageways and storage areas. The kidneys are reddish, bean-shaped structure and located just above the waist between the peritoneum and the posterior wall of abdomen. A typical kidney in an adult is 10-12 cm long, 5-7 cm wide and 3 cm thick and has a mass of 135-150 g.
Under normal circumstances the two kidneys are able to do the following functions:
Regulating of blood PH; the kidneys excrete an amount of hydrogen ions (H+) and conserve bicarbonate (HCO3-). Regulating blood pressure; the kidneys produce rennin, which activate the rennin-angiotensin-aldosterone pathways. Maintaining blood osmolarity; by regulating loss of water and loss of solutes in the urine, the kidneys maintain constant blood osmolarity.
Regulating blood glucose; the kidneys can use the amino acids glutamine in gluconegenesis. So they can release glucose into blood to help maintain a normal blood glucose level. Production of hormones; calctirriol (active form of vitamin D) which helps regulate calcium homeostasis and erythropoietin which stimulates the production of red blood cells. Excreting waste and foreign substances; by forming urine which contains the waste substances that have no useful functions in the body.
The above mentioned kidney functions based on the functional unit of the kidney called nephron. Each kidney contains about 1 million nephrons. The nephron is a tube closed at one end and open at the other and in between it consists of Bowman's capsule, Glomerulus, Proximal convoluted tubule, Loop of Henle, Distal convoluted tubule and collecting tubule. About 170-200 liters of water are filtered through the kidneys everyday, but about 1-2 liters are excreted from the body as urine.
To produce urine, nephrons and collecting ducts perform three basic processes:
- Glomerular filtration: water and most blood solutes in the blood plasma move across the wall of glomerular capillaries into the glomerular capsule and then into the renal tubule.
- Tubular reabsorption: as filtered fluid flows along the renal tubule and through the collecting duct, tubule cells reabsorb about 99% of filtered water and many solutes.
- Tubular secretion: as the fluid flows along the tubule and through the collecting duct, the tubule and duct cells secrete other materials, such as wastes, drugs and excess ions into the fluid.
Each kidney connects to bladder by ureter, which is tube like structure that provides drainage from the kidney to the bladder during the process of urine formation. Bladder acts by means of contraction to expel urine from the body. In order for the kidney to work properly the renal arteries deliver about 25% of resting cardiac out put.
Glomerular filtration (GF) normally occurs at rate of about 120-150 ml/min. There are significant forces which are involved in glomerular filtration, glomerular capillary blood pressure which induced a blood pressure within the glomerular capillary depending on the heart contraction and on the peripheral resistance provided by efferent arterioles. The other significant force is the plasma colloid osmatic pressure which occurs due to impermeability to protein through the glomerulus. The permeability depends on the molecular size and the electrical charges. The positively charged molecules easily filtered than the negatively charged one because the glomerular endothelium layer carry negative charges that repel the protein particles and not allowing them to be filtered.
In Bowman's capsule hydrostatic pressure, there will be high force to push fluid out of Bowman's capsule into glomerulus. Any changes occur in these forces will lead to change in glomerular filtration rate (GFR).
Glomerular filtration rate (GFR) is a measurement of the amount of glomerular filtrate (a substance similar to blood plasma but without proteins) formed in the kidneys each minute. It can be assessed by measuring the excretory ability and the substance level in plasma that freely filtered through the glomerulus. Some of the substances will not appear in the glomerular filtrate unless they have reached a certain concentration in blood. Glucose is such a substance that does not appear in the urine until it reaches high concentration in the blood (11.0 mmol/L). Whereas other substances like creatinine excreted without appreciable reabsorption. Creatinine is an endogenous substance, an end product of nitrogen metabolism formed through a series of enzymatic reaction in the liver. The contraction of skeletal muscle involves both creatine and ATP (adenosine triphosphate) in the presence of creatine kinase enzyme. The creatine formed from phosphocreatine gives the final end product creatinine which is instantly filtered at glomerulus without any tubular reabsorption. Therefore creatinine can be used to estimate the clearance ability of kidney, but it is not a perfect marker as it is secreted. This involves the measurement of substance concentration in urine and plasma using the following clearance formula:
(U/P) * (V/T) = mls/min
Diseases affecting the kidneys can damage glomerular or tubular function. Failure of renal function may occur rapidly producing the syndrome of acute renal failure which is characterized by rapid loss of renal function with retention of urea, creatinine, hydrogen ions and other metabolic products. However chronic renal failure develops often over many years leading to end-stage of renal failure where patients require either long term dialysis or a successful renal transplant to survive. Diabetes and hypertension are the two commonest causes of chronic renal failure with other causes including glomerulonephritis of any type
Aim of the test
To estimate renal function in two different patients using creatinine clearance test.
Materials and method
Please refer to medical biochemistry practical book (BMS2).
The equation obtained from the graph used for the calculation of creatinine concentration is:
Y = 0.0008 X
Where: Y = absorbance X = concentration of creatinine in umol/L.
P 1: X = 0.073/0.0008 = 91.25 umol/L
P 2: X = 0.346/0.0008 = 432 umol/L
U 1: X = 0.621/0.0008 = 776.25 x 21 = 16301.25 umol/L
U 2: X = 0.736/0.0008 = 468.75 x 21 = 9843.75 umol/L
P1 is plasma of patient 1.
P2 is plasma of patient 2.
U1 is urine sample of patient 1
U2 is urine sample of patient 2
Therefore the creatinine clearance is calculated by using the following formula:
(U/P) * (V/T) mls/min
U = urine creatinine umol/L
P = plasma creatinine umol/L
V = volume of urine passed in given time
T = time of collection
- Creatinine clearance for patient 1:
= 16301.25/91.25 * 1000/1440
= 211.438 * 0.694
= 124 mls/min
Creatinine clearance for patient 2:
= 9843.75/ 432 * 3000/1440
= 22.786 * 2.083
= 47.46 mls/min
From the above results I conclude that patient 1 has got normal renal function whereas patient 2 has renal failure.
The creatinine calibration graph shows good linearity which indicates that the patient's results obtained are correct.
The clearance test more often concern about how much of a specific substance the kidney can remove from a given volume of blood in a stated period. In this experiment the creatinine clearance test was used to estimate GFR in two different patients based on the principle of Jaffe reaction (picric acid with alkaline solution from red to orange complex). A standard curve was produced using the absorbance reading against the standard concentration. A straight linear relationship obtained which means that as the optical density increase the creatinine concentration will increase. The equation obtained from the graph (Y = 0.0008 X) is used to calculate the plasma and urine creatinine concentration of two patients.
The plasma creatinine concentration for patient 1 is 91.25 umol/L, which means it is within the normal reference ranges (adult 60-120 umol/L).Marshal, (2000). Also the urine creatinine concentration (19293.75umol/L) for the same patient support the plasma concentration in which simply means that creatinine excretion by kidney was regularly. In contrast, patient 2 has got increased plasma creatinine concentration when compared with normal reference range which is 432 umol/L. That means the creatinine being not filtered regularly into urine.
There is no history of patient is provided and it is not stated whether the patient is male or female which can aid the diagnosis. However, there is not much difference between male and female normal reference ranges (adult 60-120 umol/L).
The clinical data are good in detecting the presence of renal disease, by its effect on renal function and is in assessing its progress but they will not assess the determination of the cause of the disease. Therefore several factors should be kept in mind when doing creatinine estimation. These factors are: there will be reduced creatinine concentration in children, women and during pregnancy. Meals which contain meat will raise plasma creatinine, also certain drugs (e.g. salicylates, cimetidine) increase plasma creatinine by inhibiting tubular secretion of creatinine.
From the result, it is noticeable that patient 1 has got normal creatinine clearance (124 mls/min) when compared with the reference ranges. This means that this patient got normal GFR and normal renal functioning units.
The creatinine clearance for patient 2 is very low (47.4 mls/min) when compared with the normal reference range and with patient 1 who has normal GFR. As mentioned earlier the plasma creatinine was high and the urine creatinine was low for this patient which gives strong suggestion that this patient represent with kidney disorder mostly chronic failure. Although the clinical finding help the diagnosis, but the requirement of further test is needed to identify the cause and to confirm disorder.
Renal failure is divided into two types, acute renal failure and chronic renal failure. An acute onset is severe enough to cause kidney failure and is characterized by oliguria (less urine). The major cause of acute failure is tubular necrosis. Other common causes are loss of huge amount of blood during accident or surgery, toxic drugs and poising e.g. lead, or infection. Acute renal failure may develop gradually to a chronic renal failure.
Chronic renal failure occurs when disease or disorder damages the kidneys so that they can no longer remove fluids and wastes from the body or maintain proper levels of kidney-regulated chemicals in the bloodstream. The four most common causes of chronic kidney failure are:
Diabetes: Diabetes Mellitus (DM), both insulin dependent (IDDM) and non-insulin dependent (NIDDM), occurs when the body cannot produce and/or use insulin, the hormone which is necessary for the body to process glucose. Long-term diabetes may cause the glomeruli to gradually loss function. In fact, progression may be slow gradual which means the symptoms do not occur until the GFR falls below 15 ml/min. Marshal, (2000).
High blood pressure: hypertension is both cause and result of kidney failure. The kidney can become stressed and ultimately sustain permanent damage from blood pushing through them at excessive pressure over long periods of time.
Glomerulonephritis is an inflammation of glomeruli, or filtering units of the kidney. The filter in glomerulus is damaged; often small holes are made mostly due to streptococcal infection.
Polycystic kidney disease: it is an inherited disorder that causes cysts to form in the kidneys. These cysts impair the regular functioning of the kidney. Less common causes of chronic kidney failure are kidney cancer, obstructions such as kidney stones, pyelonephtitis.
Initially, symptoms of chronic kidney failure develop slowly. Even individuals with mild to moderate kidney failure may have few symptoms in spite of increased urea in their blood. Among sings and symptoms that may be present at this point are frequent urination during the night and high blood pressure. Most symptoms of chronic kidney failure are not apparent until kidney disease has progressed significantly. Common symptoms are:
Anaemia: The kidneys are responsible for production of erythropoietin, a hormone that stimulates red cell production. If the kidney disease causes shrinking of the kidney, the red cell production is hampered.
Bone and joint problems: The kidneys produce vitamin D, which help in absorption of calcium and keeps bones strong. In patients with kidney failure, bones may become brittle, and in children, normal growth may be stunted. Joint pain may also occur as a result of unchecked phosphate levels in the blood.
Foamy or bloody urine: Protein in the urine may cause it to foam significantly. Blood in the urine may indicate bleeding from diseased or obstructed kidneys, bladder, or ureter.
Hypertension or high blood pressure: The retention of fluids and sodium causes blood volume to increase, which in turn causes blood pressure to rise.
Low back pain: Pain where the kidneys are located, in the small of the back below the ribs.
Nausea, loss of appetite and vomiting: Urea in the gastric juices may cause upset stomach and this can lead to malnutrition and weight loss.
- What protein would not be detected by dip sticks, and how would you detect it?
Bence Jones proteins are low molecular weight proteins (light chains of immunoglobulin) and found in urine in patient with Myeloma. They are small enough to move quickly and easily through the kidney into urine.
These proteins can be detected by doing protein electrophoresis of concentrated urine
- What is the clinical finding in the unusual condition orthostatic proteinuria?
Orthostatic proteinuria is a benign condition that effect children and young adults. The patients are only exhibiting proteinuria after they have been standing up. Orthostatic proteinuria arises as a result of an increase in the hydrostatic pressure in the renal veins. Protein will not be detectable in an early morning sample when tested using dipstick. The patient is instructed to empty the bladder just before going to bed, and the test for protein is performed on a specimen of urine passed the following morning, immediately after getting up the condition is usually observed in only some of the urine samples passed when up and about (with good prognosis). The prognosis is less good in patients in whom proteinuria is always detected when they are up and about.
- What are the factors predisposing to renal stone formation?
A kidney stone is a hard mineral and crystalline material formed within the kidney or urinary tract. Kidney stones are a common cause of blood in the urine and pain in the abdomen.
The factors predisposing to renal stone formation are:
- Reduction of fluid intake
- Increased exercise with dehydration
- Medications that cause hyperuricemia (high uric acid) and excessive intake of calcium supplements
- Diet can also influence stone formation e.g. oxalate (ice tea and colas)
- Urinary tract infections
- Family history of urinary calculi
- Certain diseases :hyperparathyroidism (causes calcium loss from bone), renal tubular acidosis(causes a deficiency in urinary citrate, a stone inhibitor)
- Urinary stagnation
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