Renal function tests
Chronic kidney disease is associated with anaemia, with the level of renal function inversely correlated with the severity of anaemia. For this reason, it is important to measure and monitor renal function to ensure timely diagnosis and monitor the effects of medical interventions.
Urea and electrolytes
Serum urea and electrolyte concentrations form a part of the standard battery of clinical chemistry tests carried out using the Sequential Multiple Analyzer with Computer (SMAC). Urea is freely filtered by the kidneys, but can also be partially reabsorbed. Therefore, although blood urea nitrogen (BUN) is commonly used to assess renal function, it has only modest utility.
GFR (glomerular filtration rate)
GFR is the volume of water filtered out of the plasma by the nephron in the kidneys each minute and is an important index of kidney function. GFR can be measured using filtration markers such as inulin, iohexol or iothalamate but such tests are complex and expensive. GFR is difficult to measure in routine clinical practice.
Creatinine clearance
Creatinine clearance is defined as the rate at which creatinine is cleared from the blood plasma by the kidneys and can be calculated from urine and serum creatinine levels. Because creatinine is freely filtered by the kidneys and is not reabsorbed, creatinine clearance can be used as an indicator of kidney function but is not as accurate as eGFR.
Estimated (e)GFR
eGFR is a more accessible diagnostic measure that does not require specialized tests or equipment takes into consideration serum creatinine concentration, as well as patient age, gender, and race.
The simplified Modification of Diet in Renal Disease Study Group (MDRD) formula is the most commonly used and most accurate method of estimating GFR.1, 2
The simplified MDRD formula for estimating GFR is:
| GFR = 186 x (serum creatinine) -1.154 x (age) -0 .203 x SM x RM |
Where:
GFR – glomerular filtration rate (mL/min/1.73 m2)
Serum creatinine (mg/dL)
Age (years)
SM (sex multiplier) is calculated as follows:
Men: SM = 1
Women: SM = 0.742
RM (race multiplier) is calculated as follows:
Black: RM = 1.212
Other: RM = 1
Normal ranges:
Male: 97 to 137 ml/min.
Female: 88 to 128 ml/min.
3
Next in this section (Comorbidities tests)
References
- Levey AS, Bosch JP, Lewis JB, et al. A more accurate method to estimate glomerular filtration rate from serum creatinine: a new prediction equation. Modification of Diet in Renal Disease Study Group. Ann Intern Med 1999;130:461–70.
- Myers GL, Miller WG, Coresh J, et al. Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease. Clin Chem 2006;52:5-18.
- Medical Encyclopedia. Available at: http://www.nlm.nih.gov/medlineplus/ency/article/003611.htm
Accessed on: January 25, 2007.
