Different ways of calculating GFR and which are better for different conditions
Historically, the Cockroft and Gault Equation was used to estimate creatinine clearance, but it has been largely supplanted by the MDRD Equation, which estimates GFR (rather than creatinine clearance). The newer CKD-EPI Equation is the least biased of the methods available to estimate the GFR. • These equations were developed primarily among individuals with CKD; consequently, all are less accurate at GFRs above 60 ml/min/1.73 m2. Of the three, the CKD-EPI equation is the most accurate at higher GFRs and is preferred for estimating GFR in the general population. These equations were developed in individuals with stable serum creatinine levels and therefore should not be used to estimate GFR in patients with acute renal injury.
Earliest marker of kidney damage
Urine dipsticks are more sensitive for urine protein than they are for albumin, detecting protein concentrations of 10mg/dl or greater, but requiring 30mg/dl of albumin for detection. New dipsticks specific for albumin are also available that are more sensitive. Both types of urine dipsticks are insensitive for detecting non-albumin proteins such as monoclonal immunoglobulins excreted in multiple myeloma.
Causes of transient proteinuria
upright position, exercise, fever, and dehydration
When to use albumin/Cr ratio vs protein/Cr ratio
If the albumin-specific dipstick is positive, then a spot urine albumin/creatinine ratio should be performed. A spot urine albumin/creatinine ratio is preferred over a spot urine protein/creatinine ratio for quantifying and monitoring proteinuria in a patient with a positive screen, since the former is more sensitive for microalbuminuria. A spot urine protein/creatinine ratio is an acceptable alternative method for monitoring proteinuria if the spot urine albumin/creatinine ratio is high (e.g., >500 mg/g) or if non-albumin proteinuria is clinically suspected (e.g., multiple myeloma).
Screening for proteinuria vs quantifying proteinuria
• Screening for proteinuria is done with the urine dipstick; quantification is done with spot urine albumin/creatinine or protein/creatinine ratios.
Diagnosis for diabetic nephropathy is done how
• A patient presenting with CKD who has diabetes, persistent albuminuria, and diabetic retinopathy can be diagnosed with diabetic nephropathy without renal biopsy, unless clinical evidence suggests another etiology.