The Importance of Uric Acid and Creatinine

Uric acid is a weak organic acid, the end product of purine nucleotides degradation. The findings of human pathological levels of uric acid in serum and urine have in most patients serious clinical implications. Uric acid is a useful diagnostic tool as screening for most of purine metabolic disorders. The importance of uric acid measurement in plasma and urine with respect of metabolic disorders is highlighted. Not only gout and renal stones are indications to send blood to the laboratory for uric acid examination.

Also familial nephritis, neurological abnormalities with mental retardation are reasons to know uric acid levels in blood and urine.

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Clinical significance:

In serum

Physiologic changes in serum concentration of uric acid About 350 mg of uric acid are daily produced by endogenous synthesis, while about 300 mg/day are taken by food. In plasma at pH 7. 4, uric acid is found in the ionized form of monosodium and monopotassium urate, and only a minor portion as a free acid.

About 90% of uric acid filtered in glomeruli is normally reabsorbed in renal tubules. Uric acid is normally excreted from the body via kidneys (80%) and intestine (20%). About 4. 76 mmol (800 mg) are excreted per day. Extreme physical exercise induces a significant increase in the concentration of uric acid.  Starvation and fat rich diet increase the concentration of uric acid in serum.

Pathologic changes in serum concentration of uric acid: Increased values of uric acid in: athetoid cerebral palsy with mental deficiency and self-mutilation, coronary artery disease, diabetic keto-acidosis following intravenous fructose, Down’s syndrome (some cases), excessive ethyl alcohol intake, gout, gross tissue destruction, heavy chain disease, hemolytic anemias, hyperlipoproteinemia type, lead poisoning, myeloid leukemia, pernicious anemia (especially after treatment), Pneumonia, primary and secondary polycythemia, primary hyperoxaluria, pyrazinamide therapy, Tangier disease, uremia, von Gierke’s glycogen storage disease.  Decreased values of uric acid in: acromegaly (some cases), administration of uricosuric drugs, Fanconi syndrome, hepatolenticular degeneration, xanthiuria.

In urine

Physiologic changes in urine concentration of uric acid Uric acid is mostly excreted in urine (about 75%). The uric acid from glomerular filtrate is almost completely reabsorbed in proximal tubules. The urates in final urine derive from active secretion of uric acid in distal tubules. Urinary urate excretion after intake of food rich in purines or upon abundant intake of xylitol, and id decreased with low-protein and high-carbohydrate, high-fat diet.

Pathologic changes in urine concentration of uric acid: Increased urine uric acid concentration in: acute lymphocytic leukemia, acute myelocytic leukemia, adult respiratory distress syndrome, bacterial meningitis, cerebral embolism, cerebral hemorrhage, cerebral infarction, cerebral thrombosis, chronic myelocytic leukemia, cystinosis, encephalomyelitis, familial periodic paralxsis, gout, hepatolenticular degeneration, Leach-Nyhan syndrome, manic depressive disorder,  myelofibrosis,  osteomalacia, paranoid states and other psychoses, polycythemia rubra vera, proximal renal tubular acidosis regional enteritis or ileitis, sickle cell disease, tuberculous meningitis, ulcerative colitis, viral hepatitis. Decreased urine uric acid concentration in: folic acid deficiency, toxic effects of lead, xanthiuria.


Creatinine is an amino acid derivative with a molecular mass of 113 Da. It is a waste product of creatine and phosphocreatine and is found almost exclusively (90%) in skeletal muscle tissues Clinical importance of creatinine is the indicator of a good kidney function. High creatine means that the kidney is not filtering well or not in good function. Used in the diagnosis and treatment of certain renal diseases, in monitoring renal dialysis, and as a calculation basis for measuring other urine analytes.

Creatinine is used routinely as part of a comprehensive or basic metabolic panel; if your doctor suspects that you are suffering from kidney dysfunction; and at intervals to monitor treatment for kidney disease or kidney function while on certain medications. Creatinine is critically important in assessing renal function because it has several interesting properties. In blood, it is a marker of glomerular filtration rate; in urine, it can remove the need for 24-hour collections for many analytes or be used as a quality assurance tool to assess the accuracy of a 24-hour collection.

The reference ranges for serum creatinine and urine creatinine are listed below. The level of serum creatinine is maintained by the balance between its generation and excretion by the kidneys. Levels are affected by factors that influence the generation, glomerular filtration, and tubular secretion of serum creatinine. There is considerable variation in the excretion of creatinine based on individual patient factors, time, and method of testing.

Since creatinine is generated in a steady manner and can be measured very simply from blood samples, it has become a useful test to estimate glomerular filtration rate (GFR), a measurement of kidney function. The reference range of serum creatinine for men is 60 to 110 micromole/L (0. 7 to 1. 2 mg/dL) and for normal women is 45 to 90 micromole/L (0. 5 to 1. 0 mg/dL). Serum creatinine-based equations have been derived for the estimation of GFR and are mainly used for the systematic staging of chronic kidney disease (CKD).

However, the utility of the estimation formulas of GFR in the acute clinical setting has not yet been validated. Several web-based GFR calculators are readily available to estimate GFR from serum creatinine values Significance  Because creatinine is excreted by the kidneys, its level in the blood is considered an indicator of kidney health. When the kidneys are functioning normally, the blood creatinine level is relatively constant day to day, though minor increases can occur after a high-protein meal. Causes of Abnormal Creatinine

Increased blood creatinine is usually a sign of problems with kidney function. The creatinine level is also raised with injury to muscle and during increased breakdown of muscle tissue. Increases in muscle mass will also raise the level of serum creatinine. Conversely, decreased muscle mass will decrease blood creatinine. Kidney Damage and Creatinine Any disease that affects the filtration process of the kidneys will tend to raise serum creatinine levels over time. Doubling of serum creatinine levels is indicative of a 50 percent reduction in the filtration rate of the kidneys.

Diseases linked to increased creatinine levels include glomerulonephritis, pyelonephritis, diabetic nephropathy and conditions such as shock and congestive heart failure that reduce blood flow through the kidneys. Muscle Damage and Creatinine Muscle damage (rhabdomyolysis) releases a protein called myoglobin into the bloodstream. Large amounts of myoglobin are toxic to the kidneys so the serum creatinine levels rise. Rhabdomyolysis can result from trauma. It is also a side effect of certain drugs, including the statins

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The Importance of Uric Acid and Creatinine. (2016, Sep 03). Retrieved from