Test ID SAT24 Supersaturation Profile, 24 Hour, Urine
Useful For
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
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 |
Special Instructions
Method Name
AMMP, CITP, OXUP: Enzymatic
USOMP: Freezing Point Depression
SULFP: High-Performance Ion Chromatography (HPIC)
CALCP: Photometric
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
UNP: Kinetic UV Assay
Reporting Name
Supersaturation, USpecimen Type
UrineOrdering Guidance
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.
Necessary Information
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.
Specimen Required
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.
Specimen Minimum Volume
25 mL
Specimen Stability Information
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Urine | Refrigerated | 14 days |
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.
Reference Values
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
≥12 months: 150-1,150 mOsm/kg
pH
4.5 to 8.0
ALL REFERENCE RANGES BELOW ARE BASED ON 24-HOUR COLLECTIONS.
SODIUM
Reference values have not been established for patients who are younger than 18 years of age.
POTASSIUM
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
≥18 years: 51-269 mg/24 hours
Reference values have not been established for patients who are younger than 18 years of age.
CHLORIDE
Reference values have not been established for patients who are younger than 18 years of age.
PHOSPHORUS
≥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: ≥18 years: 200-1,000 mg/24h
Female: ≥18 years: 250-750 mg/24h
Reference values have not been established for patients who are younger than 18 years of age.
Male: ≥18 years: 930-2,955 mg/24h
Female: ≥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
≥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
Interpretation
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.
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 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
CPT Code Information
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
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 | In Process |
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 | In Process |
21045 | Sodium Urate Crystal | In Process |
CLDUR | Collection Duration | 13362-9 |
VL38 | Volume | 3167-4 |
21060 | Interpretation | 69051-1 |
Forms
If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.
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 US Food and Drug Administration.Day(s) Performed
Monday through Friday