eGFR values derived from serum creatinine are frequently inaccurate when compared against GFR reference methods. The cause of this inaccuracy is likely related to non-functional factors, including unmeasured muscle mass and tubular secretion of creatinine.
It is only an estimate of kidney function and a significant error is possible. The eGFR is most likely to be inaccurate in people at extremes of body type e.g. patients with limb amputations, severely malnourished and morbidly obese individuals.
However, the eGFR may not be accurate if you are younger than 18, pregnant, very overweight or very muscular. In addition, other tests such as an ultrasound or a kidney biopsy may be ordered to find a cause of your kidney disease.
Key Points
Increased blood volume and increased blood pressure will increase GFR. Constriction in the afferent arterioles going into the glomerulus and dilation of the efferent arterioles coming out of the glomerulus will decrease GFR. Hydrostatic pressure in the Bowman's capsule will work to decrease GFR.
gFR declines with age, even in people without kidney disease. If your GFR is between 60 and 89... People with mildly low gFR (between 60 and 89) may not have kidney disease if there is no sign of kidney damage, such as protein in their urine.
The estimated glomerular filtration rate (eGFR) is variable and it relies on a blood test, which may have day to day variations and it is an "estimation". Hence, the more times you do the test, the more accurate will be the estimate. It can depend on some food that you eat.
In this population-based study, we examined factors associated with glomerular filtration rates (GFR) in both genders. The findings of our study showed that obesity, diabetes, blood urea nitrogen, atherogenic factor, hypertension, meat consumption, and smoking were associated with lower GFR.
Dehydration does cause the serum creatinine to rise and the estimated glomerular filtration rate (eGFR) will, accordingly, fall. The degree of change is generally proportional to the degree of dehydration. Severe dehydration can actually cause acute kidney injury and may lead to a need for dialysis therapy.
Of those who fasted, 11.1% had a drop in Glomerular Filtration Rate (eGFR) of 20% or more. Those who did not fast (16.7%) presented a similar drop. Conversely, among the few who attempted to fast and had to stop, half showed a drop in eGFR of more than 20%.
Healthcare providers may tell you not to eat or drink anything, except water, after midnight. You may also be asked not to eat any cooked meat the night before the test. It can increase the level of creatinine in your blood and affect your GFR results.
Normal Results
Older people will have lower than normal GFR levels, because GFR decreases with age. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
Amputees, paraplegics, bodybuilders, morbid obese. Muscle-wasting disease or a neuromuscular disorder.
Muscle Mass
As such, reductions in muscle are associated with reduced creatinine clearance, resulting in an overestimated eGFR. Conversely, higher muscle mass is associated with increased creatinine and underestimated eGFR.
If the decrease in the estimated glomerular filtration rate (eGFR) is due to acute kidney injury with a sudden decrease in kidney function, this can commonly be reversed. If the kidney disease is due to chronic kidney disease (CKD), the recovery of eGFR is usually not possible.
If volume depletion is severe, GFR falls, but it has been thought to be completely reversible with hydration, unless ischemia results in acute kidney injury (AKI). Nevertheless, AKI is thought be largely reversible. Hence, dehydration has not been classically considered a risk factor for chronic kidney disease (CKD).
*Other factors that can affect eGFR include: pregnancy, being over the age of 70, unusual muscle mass, cirrhosis (a disease caused by scarring in the liver), nephrotic syndrome (a condition caused by having too much protein in your urine), a past solid organ transplant, and some medications.
The only way to adjust GFR from moment to moment is to change glomerular blood (hydrostatic) pressure. the ability of the kidneys to maintain a relatively stable GFR in spite of the changes (75 - 175 mmHg) in arterial blood pressure.
Some studies have shown that GFR may increase over time in people at all stages of kidney disease by: Controlling blood pressure. You can manage high blood pressure through exercise, diet, stress reduction, and limiting alcohol, among other lifestyle choices. Making sure you're not deficient in vitamin D.
In obese patients with altered renal function, weight loss, particularly if achieved by surgical interventions, improves proteinuria, albuminuria and normalizes GFR.
The authors concluded that sustained high urine volume and low Uosm are independent risk factors for faster GFR decline in patients with chronic renal insufficiency. Thus, high fluid intake does not appear to slow renal disease progression in humans.
Rapid GFR decline, defined as an annual GFR loss of >3 mL/min/1.73 m2, represents a magnitude of change three times the rate of what is expected in normal physiology and corresponded to 25% of the cohort of the Cardiovascular Health Study with the largest decline in GFR [23, 24].