Kidney function tests are a panel of investigative tests that determine if the kidneys are working efficiently or not. The tests involve simple blood and urine analysis that can help identify problems with the kidneys such as presence of renal disease, monitoring the treatment response of kidneys, and determining the progression of renal disease. KFT/RFT are also performed when a patient suffers from other disorders, like diabetes or hypertension, that may damage the kidneys.
Factors involved to understand the normal range of KFT/RFT levels:
The normal serum creatinine levels in women is 0.6-1.1 mg/dL and in men it is in the range of 0.7-1.3 mg/dL.
The normal range of glomerular filter rate (GFR) in healthy adults is 140 mL/min/1.73m2. Above 90 is considered normal.
A normal albumin (mcg/L) to creatinine (mg/L) ratio is a level of less than 30 mg/g. Albumin to creatinine ratio (ACR) is generally low when kidneys are functioning normally.
A normal range of blood urea nitrogen (BUN) for adults and children is 7-20 mg/dL. These values vary from laboratory to laboratory.
Urinalysis – A urinalysis screens for the presence of protein and blood in the urine to rule out albuminuria etc. Normal urine protein is upto 150 mg per day.
A creatinine level higher than 1.2 mg/dL in women and 1.4 mg/dL in men is an indication of kidney dysfunction. High levels of creatinine are indicative of severe kidney disease, muscle disease, diabetes, dehydration, heart problems, overactive thyroid glands, etc. When kidney function decreases by 50%, this is the time when a rise in serum creatinine can be detected.
BUN level rises with decrease in kidney function. A level above 20 mg/dL indicates kidney damage. High BUN levels can also indicate dehydration, urinary tract obstruction, congestive heart failure, etc. BUN levels also increase when there are burn injuries.
Slightly raised ACR levels indicate early stage kidney disease. A significant increase in the ACR indicates severe kidney disease. ACR of 30-300 for more than three months points to chronic kidney disease.
Early kidney problems may not show signs and symptoms. However, the progression of problems gives rise to various symptoms. Some common symptoms that may indicate high BUN levels are:
High levels of creatinine in blood could give rise to symptoms such as:
High levels of protein in the urine, called proteinuria, is sign of severe kidney damage. Signs and symptoms are only visible when the levels have reached to a significantly higher level. These symptoms include swelling of the ankles, face, hands, or legs.
Creatinine levels are generally low in muscular young and middle aged people. They are also low in conditions such as malnutrition, severe weight and muscle loss, and chronic illnesses. Lower levels of creatinine generally mean liver disease or malnutrition.
BUN levels rarely get low. In cases where it is low, it could indicate problems such as:
A GFR below 60 is a sign of inefficient functioning of kidneys. A GFR below 15 indicates kidney failure and the patient may need treatment such as dialysis or a kidney transplant. An eGFR less than 60mL/min/1.73m2 persisting for more than three months is indicative of chronic kidney disease. Estimation of the GFR is used to determine the presence of renal impairment and if reduced over a specified period, can identify the presence and stage of chronic kidney disease.
Symptoms of low creatinine levels depend upon the reason for low levels. These symptoms may include:
Abnormal levels of the panel of tests do not necessarily indicate problems with the kidneys. Certain factors and lifestyle options also affect the levels of these tests.
Factors such as high protein diet, intense exercise, and certain medications such as antibiotics, and over-the-counter medications can lead to an increase in the creatinine levels. Instead, cutting back on intense exercise sessions and doing yoga is often recommended. Reducing red meat and other sources of protein from the diet, staying hydrated, eating more fibers, etc. is also advised.
The most effective way to lower BUN levels is to stay properly hydrated. A low protein diet, avoiding diuretics, and reducing intake of prescription drugs can help maintain normal BUN levels.
Avoiding processed foods, following a low-salt and low-protein diet, and certain lifestyle changes can help maintain normal GFR levels. In cases of diabetes, it is important to keep the sugar levels under control to prevent decrease in GFR.
There are no risks associated with simple blood and urine analysis tests. In rare cases, there are side effects such as bleeding or infection at the site of puncture, hematoma, and fainting.
As there are many factors that can affect the levels of creatinine, blood urea nitrogen, and GFR, it is necessary to confirm the diagnosis of kidney disease. The doctor may order imaging tests such as ultrasound or CT scans to determine the size, presence of kidney stones, tumors, or any other structural defects that may be present in urinary tract or kidneys. A kidney biopsy is also ordered if required.
There are certain precautions that may be required to be taken before the test. Avoiding meat, medications, and diuretics 24 hours before the test is generally advised. Abnormal levels of these tests does not necessarily indicate kidney damage and hence, confirmation of diagnosis is important. Talking to health care provider about treatment options can help prevent kidney disease.
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