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Test ID: SAT24 Supersaturation Profile, 24 Hour, Urine

Reporting Name

Supersaturation, U

Useful For

Diagnosis and management of patients with renal lithiasis:

-In patients who have a radiopaque stone, for whom stone analysis is not available, the supersaturation data can be used to predict the likely composition of the stone. This may help in designing a treatment program.


Aiding in identification of specific risk factors for stones


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


Evaluation of renal excretion of acid and urine pH


Estimation of a patient's protein intake

Clinical Information

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.


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 nonstone formers, on average, the DG is even more positive in those individuals who do form kidney stones. The "normal" 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 nonstone formers. Those DG values that are outside the expected range in a population of nonstone 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) and a higher urine pH 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.

Profile Information

Test ID Reporting Name Available Separately Always Performed
SUPST Supersaturation, U No Yes
NAUP Sodium, U Yes, (order NAU) Yes
KUP Potassium, U Yes, (order KUR) Yes
CALCP Calcium, U Yes, (order CALU) Yes
MAGP Magnesium, U Yes, (order MAGU) Yes
CLUP Chloride, U Yes, (order CLU) Yes
POUP Phosphorus, U Yes, (order POU) Yes
SULFP Sulfate, 24 Hr, U Yes, (order SULFU) Yes
CITP Citrate Excretion, U Yes, (order CITR) Yes
OXUP Oxalate, U Yes, (order OXU) Yes
UPHP pH, U Yes, (order PHU_) Yes
URCP Uric Acid, U Yes, (order URCU) Yes
CTUP Creatinine, U Yes, (order CTU) Yes
UOSMP Osmolality Yes, (order UOSMU) Yes
AMMP Ammonium, 24 Hr, U Yes, (order AMMO) Yes
UNP Urea Nitrogen, U No Yes
PCTR Protein Catabolic Rate, U No Yes
DEMO4 Patient Demographics No Yes

Analytic Time

2 days; Excess capacity for this test is limited.

Day(s) and Time(s) Performed

Monday through Friday; 8 a.m.-4 p.m.

Clinical Reference

1. Werness PG, Brown CM, Smith LH, Finlayson B: EQUIL2: a BASIC computer program for the calculation of urinary saturation. J Urol 1985;134:1242-1244

2. Parks JH, Coward M, Coe FL: Correspondence between stone composition and urine supersaturation in nephrolithiasis. Kidney Int 1997;51:894-900

3. Finlayson B: Calcium stones: Some physical and clinical aspects. In Calcium Metabolism in Renal Failure and Nephrolithiasis. Edited by DS David. New York, John Wiley and Sons, 1977, pp 337-382

4. Burtis CA, Bruns DE: Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics. Seventh edition. St. Louis. Saunders, 2014

Method Name

CITP: Enzymatic

OXUP: Enzymatic using Oxalate Oxidase

USOMP: Freezing Point Depression

SULFP: High-Pressure Ion Chromatography (HPIC)

CALCP: Photometric, NM-BAPTA Reaction

MAGP: Colorimetric Endpoint Assay

POUP: Molybdic Acid

UPHP: pH Meter

NAUP, KUP, CLUP: Potentiometric, Indirect Ion-Selective Electrode (ISE)

CTUP: Enzymatic Colorimetric Assay

URCP: Uricase

AMMP: Enzymatic Assay

UNP: Kinetic UV Assay

Specimen Type


Necessary Information

1. 24-Hour volume is required.

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

Specimen Required

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

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 and 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 in Special Instructions for multiple collections.

Specimen Minimum Volume

25 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Urine Refrigerated (preferred) 14 days
  Frozen  14 days

Reference Values


Calcium oxalate: 1.77 DG

Brushite: 0.21 DG

Hydroxyapatite: 3.96 DG

Uric acid: 1.04 DG

Sodium urate: 1.76 DG





0-11 months: 50-750 mOsm/kg

≥12 months: 150-1,150 mOsm/kg








41-227 mmol/24 hours

Reference values have not been established for patients <16 years of age.



17-77 mmol/24 hours

Reference values have not been established for patients <16 years of age.



Males: <250 mg/24 hours

Females: <200 mg/24 hours

Reference values have not been established for patients <18 years and >83 years of age



51-269 mg/24 hours

Reference values have not been established for patients <18 years and >83 years of age



40-224 mmol/24 hours

Reference values have not been established for patients <16 years of age.



<1,100 mg/24 hours



7-47 mmol/24 hours



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



0.11-0.46 mmol/24 hours



Diet-dependent: <750 mg/24 hours



Normal values mg per 24 hours:

Males: 955-2936 mg/24 hours

Females: 601-1689 mg/24 hours

Reference ranges for male and female patients <18 and >83 years of age have not been established.


The expected urine creatinine excretion per 24 hours:

Males: 13-29 mg/kg of body weight/24 hours

Females: 9-26 mg/kg of body weight/24 hours


Reference ranges for male and female patients <18 and >83 years of age have not been established.

Note: To convert to mg/kg of body weight/24 hours, divide the mg/24 hours result by body weight in kg.



15-56 mmol/24 hour

Reference values have not been established for patients <18 years and >77 years of age.



5.0-16.0 g/24 hours



56-125 g/24 hours

Test Classification

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 U.S. Food and Drug Administration.

CPT Code Information



82507-Citrate excretion










84560-Uric acid


84540-Urea Nitrogen

LOINC Code Information

Test ID Test Order Name Order LOINC Value
SAT24 Supersaturation, U 81232-1


Result ID Test Result Name Result LOINC Value
CAL24 Calcium, 24 Hr, U 6874-2
UN24 Urea Nitrogen, U 3096-5
MAG24 Magnesium, 24 Hr, U 24447-5
BSA Patient Surface Area 8277-6
AMM24 Ammonium, 24 Hr, U 25308-8
PCTR Protein Catabolic Rate, U 93746-6
UPHU pH, U 27378-9
URACI Uric Acid, U 3087-4
UOSMP Osmolality 2694-8
CITRE Citrate Excretion, U 6687-8
CL24 Chloride, U 2079-2
CRETU Creatinine, U 2162-6
K24U Potassium, U 2829-0
NA24 Sodium, U 2956-1
OXLT Oxalate, U (mmol/24 h) 14862-7
PHS_U Phosphorus, U 2779-7
SULF_ Sulfate, 24 Hr, U 26889-6
21041 Calcium Oxalate Crystal 81623-1
21042 Brushite Crystal 42673-4
OXU2 Oxalate, mg/24 h 2701-1
HT5 Height (cm) 3137-7
WT4 Weight (kg) 29463-7
21043 Hydroxyapatite Crystal 81622-3
21044 Uric Acid Crystal 42678-3
21045 Sodium Urate Crystal 43423-3
CLDUR Collection Duration 13362-9
VL38 Volume 3167-4
21060 Interpretation 59462-2

Urine Preservative Collection Options

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







50% Acetic Acid


Boric Acid


Diazolidinyl Urea


6M Hydrochloric Acid


6M Nitric Acid


Sodium Carbonate








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

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