Test Id : SAT24

X-ray dyes and contrast media will affect uric acid test results.

-If a kidney X-ray with dye or computerized tomography (CT) scan with contrast has been performed, patient should wait a minimum of 1 day before starting collection.

-If a cholangiography (bile duct X-ray) has performed, patient should wait 7 days before starting collection.

-Urine must be collected before tablets have been taken for gallbladder X-ray, otherwise patient should wait 7 days before starting collection.

1. Twenty-four hour volume is required.

2. Patient's height in centimeters and weight in kilograms are required if patient is younger than 18 years.

Supplies: Diazolidinyl Urea (Germall), 5.0 mL (T822)

Collection Container/Tube: 24-hour graduated urine container with no metal cap or glued insert

Submission Container/Tube: Plastic, 60-mL urine bottle

Specimen Volume: 35 mL

Collection Instructions:

1. Collect urine for 24 hours.

2. Add 5 mL of diazolidinyl urea as preservative at start of collection or refrigerate specimen during as well as after collection.

3. Specimen pH should be between 4.5 and 8 and will stay in this range if kept refrigerated. Specimens with pH >8 indicate bacterial contamination, and testing will be cancelled. Do not attempt to adjust pH as it will adversely affect results.

Additional Information: See Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens for multiple collections.

• Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

Note: The addition of preservative or application of temperature controls must occur at the beginning of the collection.

25 mL

Diagnosis and management of patients with renal lithiasis:

-Predicting the likely composition of the stone, in patients who have a radiopaque stone, for whom stone analysis is not available. This may help in designing a treatment program.

Aiding in identification of specific risk factors for stones using a 24-hour urine collection

Monitoring the effectiveness of therapy by confirming that the crystallization potential has indeed decreased

Evaluation of kidney excretion of acid and urine pH

Estimation of a patient's protein intake

Urine is often supersaturated, which favors precipitation of several crystalline phases such as calcium oxalate, calcium phosphate, and uric acid. However, crystals do not always form in supersaturated urine because supersaturation is balanced by crystallization inhibitors that are also present in urine. Urinary inhibitors include ions (eg, citrate) and macromolecules but remain poorly understood.

Urine supersaturation is calculated by measuring the concentration of all the ions that can interact (potassium, calcium, phosphorus, oxalate, uric acid, citrate, magnesium, sodium, chloride, sulfate, and pH). Once the concentrations of all the relevant urinary ions are known, a computer program can calculate the theoretical supersaturation with respect to the important crystalline phases (eg, calcium oxalate).(1)

Since the supersaturation of urine has been shown to correlate with stone type,(2) therapy is often targeted towards decreasing those urinary supersaturations that are identified. Treatment strategies include alterations in diet and fluid intake as well as drug therapy, all designed to decrease the urine supersaturation.

SUPERSATURATION REFERENCE MEANS (Delta G: DG)

Calcium oxalate: 1.77 DG

Brushite: 0.21 DG

Hydroxyapatite: 3.96 DG

Uric acid: 1.04 DG

Sodium urate: 1.76 DG

INDIVIDUAL URINE ANALYTES

OSMOLALITY

0-11 months: 50-750 mOsm/kg

> or =12 months: 150-1,150 mOsm/kg

pH

4.5 to 8.0

ALL REFERENCE RANGES BELOW ARE BASED ON 24-HOUR COLLECTIONS.

SODIUM

> or =18 years: 22-328 mmol/24h

Reference values have not been established for patients who are younger than 18 years of age.

POTASSIUM

> or =18 years: 16-105 mmol/24h

Reference values have not been established for patients who are younger than 18 years of age.

CALCIUM

Males: <250 mg/24 hours

Females: <200 mg/24 hours

Reference values have not been established for patients who are younger than 18 years of age.

MAGNESIUM

> or =18 years: 51-269 mg/24 hours

Reference values have not been established for patients who are younger than 18 years of age.

CHLORIDE

> or =18 years: 34-286 mmol/24h

Reference values have not been established for patients who are younger than 18 years of age.

PHOSPHORUS

> or =18 years: 226-1,797 mg/24hours

Reference values have not been established for patients who are younger than 18 years of age.

SULFATE

7-47 mmol/24 hours

CITRATE EXCRETION

0-19 years: not established

20 years: 150-1,191 mg/24 hours

21 years: 157-1,191 mg/24 hours

22 years: 164-1,191 mg/24 hours

23 years: 171-1,191 mg/24 hours

24 years: 178-1,191 mg/24 hours

25 years: 186-1,191 mg/24 hours

26 years: 193-1,191 mg/24 hours

27 years: 200-1,191 mg/24 hours

28 years: 207-1,191 mg/24 hours

29 years: 214-1,191 mg/24 hours

30 years: 221-1,191 mg/24 hours

31 years: 228-1,191 mg/24 hours

32 years: 235-1,191 mg/24 hours

33 years: 242-1,191 mg/24 hours

34 years: 250-1,191 mg/24 hours

35 years: 257-1,191 mg/24 hours

36 years: 264-1,191 mg/24 hours

37 years: 271-1,191 mg/24 hours

38 years: 278-1,191 mg/24 hours

39 years: 285-1,191 mg/24 hours

40 years: 292-1,191 mg/24 hours

41 years: 299-1,191 mg/24 hours

42 years: 306-1,191 mg/24 hours

43 years: 314-1,191 mg/24 hours

44 years: 321-1,191 mg/24 hours

45 years: 328-1,191 mg/24 hours

46 years: 335-1,191 mg/24 hours

47 years: 342-1,191 mg/24 hours

48 years: 349-1,191 mg/24 hours

49 years: 356-1,191 mg/24 hours

50 years: 363-1,191 mg/24 hours

51 years: 370-1,191 mg/24 hours

52 years: 378-1,191 mg/24 hours

53 years: 385-1,191 mg/24 hours

54 years: 392-1,191 mg/24 hours

55 years: 399-1,191 mg/24 hours

56 years: 406-1,191 mg/24 hours

57 years: 413-1,191 mg/24 hours

58 years: 420-1,191 mg/24 hours

59 years: 427-1,191 mg/24 hours

60 years: 434-1,191 mg/24 hours

>60 years: not established

OXALATE

0.11-0.46 mmol/24 hours

9.7-40.5 mg/24 h

The reference value is for a 24-hour collection.

Reference values have not been established for patients who are younger than 16 years of age.

URIC ACID

Male: > or =18 years: 200-1,000 mg/24h

Female: > or =18 years: 250-750 mg/24h

Reference values have not been established for patients who are younger than 18 years of age. 

CREATININE

Male: > or =18 years: 930-2,955 mg/24h

Female: > or =18 years: 603-1,783 mg/24h

Reference values have not been established for patients who are younger than 18 years of age.

AMMONIUM

15-56 mmol/24 hour

Reference values have not been established for patients younger than 18 years and older than 77 years of age.

UREA NITROGEN

> or =18 years: 7-42 g/24h

Reference values have not been established for patients who are younger than 18 years of age.

PROTEIN CATABOLIC RATE

56-125 g/24 hours

Delta G (DG), the Gibbs free energy of transfer from a supersaturated to a saturated solution, is negative for undersaturated solutions and positive for supersaturated solutions. In most cases, the supersaturation levels are slightly positive, even in normal individuals, but are balanced by an inhibitor activity.

While the DG of urine is often positive, even in the urine of non-stone formers, on average, the DG is even more positive in those individuals who do form kidney stones. The reference values were simply derived by comparing urinary DG values for the important stone-forming crystalline phases between a population of stone formers and a population of non-stone formers. Those DG values that are outside the expected range in a population of non-stone formers are marked abnormal.

If the urine citrate is low, secondary causes should be excluded including hypokalemia, renal tubular acidosis, gastrointestinal bicarbonate losses (eg, diarrhea or malabsorption), or an exogenous acid load (eg, excessive consumption of meat protein).

A normal or increased citrate value suggests that potassium citrate may be a less effective choice for treatment of a patient with calcium oxalate or calcium phosphate stones.

An increased urinary oxalate value may prompt a search for genetic abnormalities of oxalate production (ie, primary hyperoxaluria). Secondary hyperoxaluria can result from diverse gastrointestinal disorders that result in malabsorption. Milder hyperoxaluria could result from excess dietary oxalate consumption or reduced calcium (dairy) intake, perhaps even in the absence of gastrointestinal disease.

High urine ammonium and low urinary pH suggests ongoing gastrointestinal losses. Such patients are at risk of uric acid and calcium oxalate stones.

Low urine ammonium and high urine pH suggest renal tubular acidosis. Such patients are at risk of calcium phosphate stones.

Patients with calcium oxalate and calcium phosphate stones are often treated with citrate to raise the urine citrate (a natural inhibitor of calcium oxalate and calcium phosphate crystal growth). However, since citrate is metabolized to bicarbonate (a base), this drug can also increase the urine pH. If the urine pH gets too high with citrate treatment, one may unintentionally increase the risk of calcium phosphate stones. Monitoring the urine ammonium is one way to titrate the citrate dose and avoid this problem. A good starting citrate dose is about one-half of the urine ammonium excretion (in mEq of each). One can monitor the effect of this dose on urine ammonium, citrate, and pH values, and adjust the citrate dose based upon the response. A fall in urine ammonium should indicate whether the current citrate is enough to partially (but not completely) counteract the daily acid load of that given patient.

The protein catabolic rate is calculated from urine urea. Under routine conditions, the required protein intake is often estimated as 0.8 g/ kg body weight.

The results can be used to determine the likely effect of a therapeutic intervention on stone-forming risk. For example, taking oral potassium citrate will raise the urinary citrate excretion, which should reduce calcium phosphate supersaturation (by reducing free ionic calcium), but citrate administration also increases urinary pH (because it represents an alkali load), which promotes calcium phosphate crystallization. The net result of this or any therapeutic manipulation could be assessed by collecting a 24-hour urine and comparing the supersaturation calculation for calcium phosphate before and after therapy.

Important stone-specific factors:

-Calcium oxalate stones: urine volume, calcium, oxalate, citrate, and uric acid excretion are all risk factors that are possible targets for therapeutic intervention.

-Calcium phosphate stones (apatite or brushite): urinary volume, calcium, pH, and citrate significantly influence the supersaturation for calcium phosphate. Of note, a urine pH of less than 6 may help reduce the tendency for these stones to form.

-Uric acid stones: urine pH, volume, and uric acid excretion levels influence the supersaturation. Urine pH is especially critical, in that uric acid is unlikely to crystallize if the pH is greater than 6.

-Sodium urate stones: alkaline pH and high uric acid excretion promote stone formation.

A low urine volume is a universal risk factor for all types of kidney stones.

The urine is often supersaturated with respect to the common crystalline constituents of stones, even in non-stone formers.

Individual interpretation of the supersaturation values in light of the clinical situation is critical. In particular, treatment may reduce the supersaturation with respect to one crystal type but increase the supersaturation with respect to another. Therefore, the specific goals of treatment must be considered when interpreting the test results.

1. Werness PG, Brown CM, Smith LH, Finlayson B: EQUIL2: a BASIC computer program for the calculation of urinary saturation. J Urol. 1985 Dec;134(6):1242-1244. doi: 10.1016/s0022-5347(17)47703-2

2. Parks JH, Coward M, Coe FL: Correspondence between stone composition and urine supersaturation in nephrolithiasis. Kidney Int. 1997 Mar;51(3):894-900. doi: 10.1038/ki.1997.126

3. Finlayson B: Calcium stones: Some physical and clinical aspects. In: David DS eds. Calcium Metabolism in Renal Failure and Nephrolithiasis. John Wiley and Sons; 1977:337-382

4. Burtis CA, Bruns DE: Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics. 7th ed. Saunders; 2014

5. Tiselius HG, Daudon M, Thomas K, Seitz C: Metabolic work-up of patients with urolithiasis: indications and diagnostic algorithm. Eur Urol Focus. 2017 Feb;3(1):62-71. doi: 10.1016/j.euf.2017.03.014

• Urine Preservatives-Collection and Transportation for 24-Hour Urine Specimens

The major analytes evaluated are potassium, calcium, phosphorus, oxalate, uric acid, citrate, magnesium, sodium, chloride, sulfate, ammonium, urea nitrogen and pH. The protein catabolic rate is calculated from urine urea nitrogen using the formula: Protein catabolic rate (g/day) = [(UUN+4)* 6.25] g. Given the measured urine concentrations of these analytes and the known affinity constants of the ions for each other at the given pH, a computer program (EQUIL2) calculates a supersaturation for each ion pair of interest (eg, calcium oxalate)(1). Results are expressed as a Delta G (DG) value for each ion pair. DG is the Gibbs free energy of transfer from a supersaturated to a saturated solution.(Moreira DM, Friedlander JI, Hartman C, Elsamra SE, Smith AD, Okeke Z: Using 24-hour urinalysis to predict stone type. J Urol. 2013 Dec;190(6):2106-2111. doi: 10.1016/j.juro.2013.05.115)

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This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

82340-Calcium

82436-Chloride

82507-Citrate excretion

82570-Creatinine

83735-Magnesium

83935-Osmolality

83945-Oxalate

83986-pH

84105-Phosphorus

84133-Potassium

84300-Sodium

84392-Sulfate

84560-Uric acid

82140-Ammonium

84540-Urea Nitrogen

Sample Reports

Normal and Abnormal sample reports are provided as references for report appearance.

Normal Reports | Abnormal Reports

SI Sample Reports

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