Fractional excretion

Calculated fractional excreted sodium (FeNa) less than 1% in patients with compromised baseline renal function, and less than 0.2% in patients with normal baseline renal function indicates dehydration and reduced renal perfusion. 

Obtain blood urea nitrogen (BUN), serum creatinine (SCr), calculated fractional excretion of sodium (FeNa), serum electrolytes, and arterial blood gases. 

While some clinical and laboratory findings assist in the general diagnosis of ARF, others are used to differentiate between prerenal, intrinsic, and postrenal ARF. For example, patients with prerenal ARF typically demonstrate enhanced sodium reabsorption, which is reflected by a low urine sodium concentration and a low fractional excretion of sodium. Urine is typically more concentrated with prerenal ARF and there is a higher urine osmolality and urine plasma creatinine ratio compared to intrinsic and postrenal ARF. 

Fractional excretion of Less than 1 % Greater than... 

Sodium and water balance can be maintained despite wide variations in intake with normal kidney function. The fractional excretion of sodium (FENa) is approximately 1% to 3%... 

The distal tubules secrete 90% to 95% of the daily dietary intake of potassium. The fractional excretion of potassium (FEk) is approximately 25% with normal kidney function.29 The GI tract excretes the remaining 5% to 10% of dietary potassium intake. Following a large potassium load, extracellular potassium is shifted intracellularly to maintain stable extracellular levels. 

ARF, acute renal failure BUN, blood urea nitrogen FEft a, fractional excretion of sodium Sa, serum creatinine RBC, red blood cell WBC, white blood cell. 

Simultaneous measurement of urine and serum chemistries and calculation of the fractional excretion of sodium (FENa) can help determine the etiology of ARF (see Table 75-2). The FENa is calculated as ... 

Calculate measured creatinine clearance Calculate fractional excretion of sodium Plans for renal replacement... 

Serum sodium concentration is generally maintained by an increase in fractional excretion of sodium, resulting in a volume-expanded state. The most common manifestation of increased intravascular volume is systemic hypertension. 

Fractional excretion of electrolytes (i.e., sodium, potassium, and chloride)... 

Uricosurics like probenecid, sulfinpyrasone and benzbromaron increase urate clearance and fractional excretion of filtered urate. They are used in underexcretors of urate. Uricosurics benefit patients with hyperuricemia, intact renal function and no history of nephrolithiasis. In tropical and subtropical climates where most of the Third World countries are situated, the prevalence of urolithiasis is >40%. The use of uricosurics is contraindicated in patients with a history of urolithiasis as the number and size of stones will be increased. Without an history of urolithiasis, uricosurics still should be applied with caution where the risk for dehydration is high. 

Diluted urine samples (factor 20) of a cancer patient after receiving intravenous chemotherapy with cisplatin were examined by HPLC-ICP-MS with respect to cisplatin (as the parent drug) and intermediately formed mono- and diaquacisplatin products.68 Analysis of species distribution in diluted human urine from the cancer patient revealed that approximately 40 % of the parent drug was excreted as monoaquacisplatin. The remaining fraction excreted as intact cisplatin was hydrolyzed at a high chloride concentration.68... 

The risk interpretation of biomonitoring results will tend to have additional uncertainties. That is because, in addition to the standard uncertainties encountered in risk assessment, there is the uncertainty of extrapolating from a blood or urinary concentration to an external dose. There will be variability both in the timing between sample draw and most recent exposure and in the relationship between blood concentration and dose. Those kinds of variability are compounded by uncertainty in the ability of a PK calculation or model to convert biomarker to dose accurately. For example, reliance on urinary biomarker results expressed per gram of urinary creatinine leads to an uncertain calculation of total chemical excretion per day because of the considerable variability in creatinine clearance per day. That complicates an otherwise simple approach to estimating dose. Furthermore, the conversion requires knowledge of fractional excretion via various pathways, which may not be present for a large sample of humans. The uncertainties created by these factors can be bounded via sensitivity and Monte... 

Carlo analysis, but ultimately the variability in fractional excretion and creatinine clearance needs to be understood to characterize population exposure to urinary biomarkers. 

After the equilibration period, clearance periods of 20 min are used. Urine samples are collected and perfusate is obtained at midpoint of the clearance period for the evaluation of overall kidney function. For determination of glomerular filtration rate (GFR) and fluid transport, 3H-labelled polyethylene glycol is added to a modified Krebs-Henseleit bicarbonate buffer. Electrolytes are determined in urine by standard flame photometry. Fractional excretions of water, electrolytes and test compounds are calculated. 

In each sample the concentration of a glomerular marker, such as inulin, and the concentration of the substance under study are measured. Fractional excretion of the substance and the glomerular marker are plotted versus the cumulative urinary volume. 

The most useful way to utilize urine electrolyte information is to calculate the fractional excretion (FE), which is the proportion of the filtered load that is excreted from the plasma. If both tubular function and plasma electrolyte values are normal, increases in electrolyte FE values clearly reflect a decrement in GFR. With tubular malfunction, the direction of the change in FE values depends on the net direction of electrolyte transport (i.e., FE will increase for electrolytes that are primarily reabsorbed and will decrease for secreted electrolytes) (Finco 1997 Stockham and Scott 2002). 

Carvounis CP, Nisar S, Guro-Razuman S (2002) Significance of the fractional excretion of urea in the differential diagnosis of acute renal failure. Kidney Int 62 2223-2229 Dunn SR, Qi Z, Bottinger EP et al. (2004) Utility of endogenous creatinine clearance as a measure of renal function in mice. Kidney Int 65 1959-1967... 

Kim HY, Han JS, Jeon US etal. (2001) Clinical signficance of the fractional excretion of anions in metabolic acidosis. Clin Nephrol. 55(6) 448-452... 

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