What is the most sensitive Lab test to evaluate Renal function

1.

Gharavi, Ali G., Landry, Donald W. (2024). In Goldman-Cecil Medicine (pp. 720). DOI: 10.1016/B978-0-323-93038-3.00100-3

Although the most accurate method of evaluating kidney function is a formal measurement of GFR with iothalamate, iohexol, or similar markers, thesetests are too expensive and time-consuming to be recommended for routine clinical practice. Currently, the most common methods used to estimate GFR are the serum creatinine concentration, the calculated creatinine clearance, and estimation equations based on serum creatinine. Serum creatinine is, to a first approximation, neither secreted nor reabsorbed, so the amount appearing in the urine per unit time is a measure of the amount that was filtered at the glomerulus during that period. As a result, the rate of creatinine clearance is a reasonably close estimate of the GFR. A decrement in the GFR diminishes creatinine clearance but has no immediate effect on creatinine production by muscle; as a result, the serum creatinine concentration rises. The change in serum creatinine over time indicates the tempo of the renal disease and can distinguish acute injury from chronic kidney disease. The routine use of serum creatinine alone to infer GFR is ill-advised because of the differing rates of creatinine production among individuals, mainly related to variations in muscle mass. Women and the elderly can have deceptively low serum creatinine levels despite significant declines in GFR. In addition, the inverse relationship between GFR and serum creatinine (Fig. 100-2) has important and potentially easily overlooked clinical implications. An initial small absolute rise in creatinine usually reflects a marked fall in GFR, whereas seemingly large changes in the serum creatinine level in patients with more advanced chronic kidney disease (CKD) may reflect minor changes in GFR.

2.

Food and Drug Administration (DailyMed).

Publish date: December 1, 2019.

Dosage And Administration No diet or water restriction is necessary. 2. Oral water load is begun one hour before starting the test. Start with 20 mL/kg and force any clear liquids (unless contraindicated) until the test is complete. II. Procedure: Record actual times for the collection of the blood and urine samples. 1. Empty the bladder and label the urine Urine control. 2. Inject 10-30 µCi Glofil-125 (sodium iothalamate i-125 injection) intravenously; wait 30 to 60 minutes. 3. Collect the entire urine and label Urine discard. 4. Draw 4 to 5 mL of blood into a heparinized syringe. Label Plasma #1. 5. After another 30 to 60 minutes, collect the entire urine and label Urine #1. 6. Immediately draw another blood specimen. Label Plasma #2. 7. After final 30 to 60 minute wait, collect the urine. Label Urine #2. 8. Draw the last blood specimen immediately. Label Plasma #3. III. Clearance Calculations: 1. Radioactivity of one mL aliquots of both urine and plasma are determined using a well-scintillation detector with a single channel pulse-height analyzer. Sufficiently reproducible counts are usually obtained with time settings of 2 minutes for urine samples and 20 minutes for the plasma samples.

Dosage And Administration III. Clearance Calculations: 1. Aliquots (1 mL each) of plasma and urine from each collection period are counted in a standard gamma-ray scintillation well detector. 2. All counts are corrected for background activity. 3. Glomerular filtration rate is calculated by the formula C=UV/P, in which: C = glomerular filtration rate in mL/min U= urinary concentration of radioactivity in net counts/min/mL V= urinary flow rate in mL/min P = plasma concentration of radioactivity in net counts/min/mL 4. Average glomerular filtration rate (GFR) is calculated from the rates for the individual collection periods. GFR can be expressed in terms of body weight (mL/min/kg) or body surface area (mL/min/m 2 ). 5. Unilateral glomerular filtration rates can be determined by the same technique by utilizing ureteral catheterization. Single intravenous injection Cohen 2 method: The method of Cohen, et al 2 requires little preparation, few and small blood samples, no bladder catheterization, and no constant intravenous infusion. It is simple to perform, rapid, and utilizes equipment which is readily available in most modern laboratories. I. Preparation: 1. Lugol's solution, 3 drops orally, three times a day, is administered for one or two days prior to the test. No diet or water restriction is necessary. 2. Oral water load is begun one hour before starting the test.

3.

Elsevier ClinicalKey Clinical Overview

Workup All patients at initial assessment undergo the following laboratory tests: CBC Anemia of chronic disease (may be present in mild and more progressive stages of kidney disease) Comprehensive metabolic panel including estimated GFR, calcium, phosphorous, and bicarbonate levels Urine albumin to creatinine ratio Urinalysis and urine microscopy to assess for hematuria and other sediment abnormalities, including casts Serum protein level and urine electrophoresis with immunofixation and a free serum and urine light chain assay Use in adults who have risk factors for multiple myeloma or other plasma cell dyscrasias when no other cause of chronic kidney disease is obvious Estimated GFR (creatinine) Serum creatinine is the most common filtration marker used to estimate kidney function worldwide and is inexpensive, reliably measured, and associated with risk of kidney failure and cardiovascular events Serum creatinine is a marker of muscle metabolism and is therefore influenced by muscle mass as well as tubular secretion Creatinine-based estimated GFR may be less accurate in non-White patients, and correction factors for race-based estimated GFR may lead to disparities in chronic kidney disease care Estimated GFR (cystatin C) Cystatin C is produced by all human nucleated cells and is a biomarker of glomerular filtration Cystatin C is unaffected by muscle mass or race and may have fewer non-GFR determinants than serum creatinine Cystatin C is more closely associated with cardiovascular events, costs more per assay, and lacks universal availability Albuminuria Urine albumin to creatinine ratio provides the best prognostic measure of kidney damage and is required to stage and risk stratify patients with chronic kidney disease Variability in albumin excretion requires 2 to 3 measurements to confirm presence of albuminuria or proteinuria Parathyroid hormone Hyperparathyroidism can help confirm chronicity of kidney disease in the absence of historical estimated GFR values Genetic testing