Serum creatinine

Relatively poor measure of renal function which is influenced by age, gender and body composition.

Creatinine is a non-protein nitrogenous metabolic product of creatinine phosphate, derived from skeletal muscle and dietary intake of cooked meat.

it is useful for estimating GFR because it is released into the bloodstream at a relatively constant rate and is filtered by the kidneys.

Greater than 1.5 mg/dL a strong predictor of cardiovascular disease.

Level depends on creatinine production and elimination.

Elimination mostly depends on GFR, but tubular secretion is also important, especially in patients with markedly reduced kidney function.

Serum creatinine testing should not be used as a stand alone source for assessing renal function.

Serum creatinine level is a late disease market, often increasing at 24-48 hours after the initial kidney insult.

Elevation in serum creatinine a late sign of renal damage in essential hypertension.

Affected in opposite directions by kidney function and muscle mass, and both of these factors decline with aging.

serum creatinine can be influenced by factors other than kidney function: low muscle mass, low activity levels, vegetarian diet, frailty, lower extremity amputation, advanced heart failure, or liver failure; All are associated with lower serum creatinine levels and cause GFR to be higher than actual GFR.

Conversely, serum creatinine levels may be higher in very muscular individuals, resulting in an estimated GFRA is lower than the actual GFR.

Recent ingestion of cooked meat and use of medication is tthat inhibits proximal tubule secretion of creatinine – trimethoprim, cimetidine, tyrosine kinase inhibitors, can elevate serum creatinine, leading to a reduction in estimated GFR that is not due to a true decrease in  kidney filtration function.

While muscle injury may increase creatinine release, sepsis may decrease creatinine production such that the serum creatinine may not increase despite a decrease in GFR.

Serum creatinine increases slowly after acute kidney injury.

Its limitations evaluating kidney function include numerous non-renal determinants, insensitivity to early kidney deterioration, and the lag time to rise when damage occurs.

Creatinine distributes in a large volume, approximately 60-70% of total body weight.

Increase in serum creatinine may be delayed by administration of large amounts of fluid and a positive fluid balance.

Patients with sepsis given a large amount of fluids may make acute kidney injury less recognizable.

Reaching a steady state of serum creatinine level requires all compartments in which creatinine distributes are at an equilibrium between production and elimination.

Its accuracy in the elderly has been questioned.

Admission serum creatinine is an independent risk factor for hospital mortality in patients who are hospitalized

To be used as marker of kidney function its production and protein intake must be assumed to be constant.

Strong association between a low serum creatinine values and increased hospital mortality among ICU patients.

Creatinine excretion is due to filtration (90-95%) by the kidney and 5-10% secretion by the distal tubule.

Acute kidney injury criteria include a relative increase in swum creatinine of 50% or greater from baseline within seven days or an absolute increase in serum creatinine of 0.3 mg/dL or greater within the 48 hour period.

A amino acid metabolite distributed throughout the total body water compartment and freely filtered by the glomeruli.

Factors that can deviate the generation of creatinine include extremes of muscle mass and ingestion in the diet, inhibition of secretion by the renal tubule, and interference with extratenal elimination by gut bacteria.

As GFR decreases, the percentage of creatinine excretion due to secretion increases.

In patients receiving long-term dialysis who have minimal or no residual renal function and who undergoes stable hemodialysis treatments, time averaged serum creatinine concentration is a surrogate for muscle mass, and its changes over time may represent changes in skeletal muscle mass.

In patients on chronic dialysis, the mortality risk is higher in patients with lower serum creatinine values.

A known biomarker for muscle mass and kidney function because 90% of its precursor, creatine phosphate, is stored in the muscle, its production is mostly constant, and is excretion is completely via the kidney.

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