Kidney function estimation

ASSESSMENT OF KIDNEY FUNCTION ESTIMATION OF GLOMERULAR FILTRATION RATE... 

Thiazides are the preferred type of diuretic for treating hypertension. In patients with adequate kidney function (estimated GER > 30 mL/min), thiazides are the most effective diuretics for lowering BR As kidney fnnction declines, a more potent diuretic is needed to counteract the associated increase in sodinm and water retention. In this case, a loop dinretic (e.g., furosemide dosed twice daily) should be considered. Dinretics ideally should be dosed in the morning if given once daily and in the morning and afternoon if dosed twice daily to minimize the risk of nocturnal diuresis. However, with chronic use, thiazides, potassium-sparing diuretics, and aldosterone antagonists rarely cause a pronounced diuresis. 

O Equations to estimate creatinine clearance that incorporate a single creatinine concentration (e.g., Cockcroft-Gault) may underestimate or overestimate kidney function depending on whether acute renal failure is worsening or resolving. 

Several equations have been developed to assess unstable kidney function. The Jelliffe equation (Table 22-1) estimates creatinine clearance by considering the change in serum creatinine over a specified time period.11 While it is more mathematically difficult to calculate, it better estimates creatinine clearance in patients with rapidly changing kidney function compared to an equation that only includes a single creatinine concentration. 

Identify the patient at risk for CIN—For patients likely to have reduced kidney function a measurement of the SCr level and estimation of the glomerular filtration rate can be recommended, If the glomerular filtration rate is less than 50 mL/min/l, 73 m2, particularly in combination with other risk factors, consideration should be given to alternative imaging approaches. 

Qll Which tests could be applied to estimate whether Greg s kidney function had returned to normal ... 

The clearance concept has been used in defining the pharmacokinetics of drugs since the mid-1970s. " The elearanee eoneept is based in physiology, where it is used as a measure of renal funetion (ereatinine elear-ance). Creatinine is formed from muscle breakdown at a constant rate, and thus a constant creatinine concentration in plasma results. The magnitude of this concentration is dependent on the elimination rate of ereatinine and the size of the muscle pool (formation rate). By measuring the plasma concentration and the renal excretion of ereatinine, renal clearance can be estimated and thereby kidney function indicated, as ereatinine is mainly filtered into the urine... 

The influence of age on metabolic clearance is less clear than its influence on renal function. Metabolic clearance is more variable between individuals because of the genetic control and the influence of environmental factors on the metabolic capacity. The term metabolism also encompasses many different enzyme reactions that might be influenced to different extents by age, liver disease, or genetic variables. Unlike renal disease, in which creatinine clearance provides a reasonable estimate of kidney function, not one good indicator exists for the degree of liver function impairment with respect to drug metabolizing capacity. 

P2.m. The cysteine proteinases are one of four major classes of endoproteinases that possess the ability to degrade intact glomerular basement membranes [144]. All nucleated cells produce cystatin at a stable rate. More than 99% is freely filtered by the glomerulus with little secretion or reabsorption. As a result, it has many of the ideal features for use as a marker of kidney function and eshmate of GFR. Serum cystatin C concentrations demonstrate a good inverse correlation with radionuclide derived measurements of GFR and has been shown in several studies to be superior to creatinine and comparable to iohexol clearances in estimating eGFR [145,146]. 

Figure 5. Bar graph showing estimated GFR (MDRD calculation) of patients presenting with AIN in two large case series. Although GFR does improve from presentation, patients do not return to their previous baseline kidney function and are left with chronic kidney disease. The dark bars represent data from reference 27, the light bars from reference 25.

Because control of renal function and blood pressure is multifactorial, the causal contribution of lead is difficult to isolate. A number of biomarkers (blood, tibial, and patella lead), and a variety of populafions differing by age, gender, race, and level of exposure are examined. Systohc and diastolic pressures are assessed separately and may be analyzed both as continuous or dichotomous variables. Kidney function is assessed by the serum creatinine concentration or empirical adjustments of the creatinine to estimate GFR. Large populations are required to achieve statistical significance amidst the noise of the multifactorial causality and the imprecision of outcome measures. Inconsistent results and weak correlations are, therefore, expected as smaller and smaller outcome effects are evaluated. 

Patients with hypertension may develop damage to either the renal tissue (parenchyma) or the renal arteries. Chronic kidney disease presents initially as microalbuminuria (30-299 mg albumin in a 24-hour urine collection) that can progress to macroalbuminuria and overt kidney failure. The rate of kidney function deterioration is accelerated when both hypertension and diabetes are present. Once patients have an estimated glomerular filtration rate (GFR) of less than 60 mL/m per minute or macroalbuminuria, they have chronic kidney disease, and the risk of cardiovascular disease and progression to severe chronic kidney disease increases. Strict BP control to a goal of less than 130/80 mm Hg can slow the decline in kidney function. This strict control often requires two or more antihypertensive agents. 

The serum creatinine concentration (Scr) or the reciprocal of Scr versus time should be used with caution to estimate the rate of decline in renal function in CKD patients, as these indices do not consider patient age, lean body mass, gender, diet, concomitant diseases and drug therapy, circadian rhythm, stability of kidney function, tubular secretion of creatinine, or analytic method. 

Patients undergoing screening for participation in the African-American Study of Kidney Disease and Hypertension were evaluated for kidney function based on an estimated CLcr compared with the simultaneous CLcr and I-iothalamate, and 24-hour CLcr- The simultaneous CLcr provided the best estimate of GFR. The CG method was the preferred method for estimation of GFR, based on performance and ease of use. This method was noted to underestimate the GFR by 9%, perhaps because of the increased excretion rate of creatinine by black patients. ... 

CKD has been described as a silent epidemic and is a worldwide public health problem. Three different national surveys have estimated that the prevalence of CKD is at least 5% of the adnlt population when using a serum creatinine concentration of greater than 1.2 to 1.5 mg/dL as the definition.The most representative of these studies, the Third National Health and Nutritional Examination Survey (NHANES III) ° projected that at least 10.9 million people had a decreased level of kidney function as evidenced by serum creatinine concentration (>1.5 mg/dL). The NHANES III analysis also revealed that the prevalence of CKD was significantly associated with age, race, gender, and hypertension the prevalence of CKD was higher in those of advanced age, black race, male gender, and a diagnosis of hypertension. 

Klopper JF, Hauser W, Atkins HL, Eckelman WC, Richards P (1972) Evaluation of Tc-99m-DTPA for the measurement of glomerular filtration rate, J Nucl Med 13 107-110 McAfee JG, Gagne G, Atkins HL, Kirchner PT, Reba RC, Blaufox MD, Smith EM (1979) Biological distribution and excretion of DTPA labeled with Tc-99m and In-111. J Nucl Med 20 1273-1278 Nielsen SP, Moller ML, Trap-Jensen J (1977) Tc-99m-DTPA scintillation-camera renography a new method for estimation of single-kidney function, J Nucl Med 18 112-117 O Reilly PH (1992) Diuresis renography. Recent advances and recommended protocols. Br J Urol 69 113-120... 

The kidneys receive about 20% of the cardiac output (blood flow) and filters approximately 125 ml of plasma per minute. As the patient loses kidney function, the quantity of plasma filtered per minute decreases with an accompanying decrease in clearance. The most useful estimation of creatinine clearance rate (CCr) is obtained using the following empirical formula based on the patient s age and serum creatinine level. 

The levels of cadmium in the urine and blood provide an estimate of the total amount of cadmium in the body. The amount of a spedflc protein in the urine (beta-2-microglobulin) indicates changes in kidney function. All... 

In chronic progressive renal failure, as much as 80 % of the functional renal mass can be lost before functional biomarker level rise. This means that the functional biomarkers can underestimate the actual extent of kidney injiuy and thus result in a false-negative signal. Therefore, while the functional biomarkers SCr and BUN may be helpful to estimate the impact of DIKI on a change, if any, on kidney function (i.e., GFR), they are not particularly useful tools for predicting DIKI potential or susceptibility before frank kidney injury has occurred. 

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