24-Hour Urine Protein: calculation from concentration and urine volume
What 24-hour urine protein measures and when it is ordered
24-hour urine protein is the total mass of protein excreted in the urine over a full day, expressed in mg/24h. Because protein concentration varies with hydration, a spot sample alone does not tell how much the kidney loses per day; the timed collection solves this by pooling all the urine from the period.
The 2024 KDIGO guideline recognizes 24-hour urine as the definitive way to demonstrate albumin or protein loss, but notes that the collection is difficult to control and prone to errors. For this reason, for initial testing, KDIGO itself prefers ratios in a spot sample, such as the urine albumin-to-creatinine ratio and the spot urine protein-to-creatinine ratio.
The 24-hour measurement remains useful when the total daily loss needs to be quantified, at the physician's discretion. The same collection also allows calculation of creatinine clearance, provided that urine creatinine is measured.
How to use the calculator: inputs and result
The calculator asks for two required values and the collection time:
- Urine protein, in mg/dL, from 0 to 5,000: the total protein concentration measured in the mixed urine from the collection. Example: 10.
- Urine volume of the collection, in mL, greater than zero and up to 10,000. Example: 1500.
- Collection time, in hours, prefilled with 24. If the collection lasted a different period, up to 48 hours, enter the actual time and the result is converted to 24 hours.
Values outside the ranges produce an error message explaining what to correct. The output shows the 24-hour urine protein in mg/24h, as a whole number, and in g/24h, with two decimal places.
Next to the number appears the KDIGO protein excretion category (A1, A2 or A3), applied to the whole value in mg/24h; the limits of 150 and 500 mg/24h belong to category A2. Above 3.5 g/24h, the tool adds a nephrotic-range warning. The text reminds you that an isolated result does not define kidney disease.
24-hour urine protein formula and worked example
24-hour urine protein is the product of concentration and volume, with two unit adjustments. Since 1 dL equals 100 mL, the volume in mL is divided by 100; and, if the collection did not last 24 hours, the total is multiplied by 24 and divided by the actual time:
Urine protein (mg/24h) = Protein (mg/dL) × [Volume (mL) ÷ 100] × [24 ÷ Collection time (h)]
With the standard 24-hour collection, the last factor equals 1.
Didactic example (not an interpretation of a patient): urine protein of 25 mg/dL in a collection of 1,800 mL, over 24 hours.
- Volume in deciliters: 1,800 ÷ 100 = 18 dL.
- Urine protein: 25 × 18 = 450 mg/24h, or 0.45 g/24h.
- Since 450 is between 150 and 500, the category is A2, moderately increased.
If the same urine had been collected over 12 hours, the conversion would give 450 × 24 ÷ 12 = 900 mg/24h, category A3. With the example values in the fields (10 mg/dL and 1,500 mL), the result is 150 mg/24h, exactly the lower limit of A2. Results right at the limit fall within the expected collection and assay error and call for caution.
How to understand the result in mg/24h
The result in mg/24h estimates how much protein the patient loses in the urine per day, under the conditions of that collection. KDIGO 2012 relates this protein excretion rate to three categories:
| KDIGO category | Protein excretion (mg/24h) | Description |
|---|---|---|
| A1 | below 150 | Normal to mildly increased |
| A2 | 150 to 500 | Moderately increased |
| A3 | above 500 | Severely increased |
The tool shows the corresponding category and, above 3.5 g/24h, warns that the proteinuria is in the nephrotic range, a limit used by the 2021 KDIGO guideline for glomerular diseases. KDIGO notes that albumin is only one of the types of protein in urine, so total proteinuria and albuminuria are not interchangeable.
A value above 150 mg/24h does not define kidney disease on its own. KDIGO characterizes chronic kidney disease by abnormalities present for at least three months, and Table 16 of the 2024 guideline lists causes of transient elevation of urine protein, such as exercise, urinary tract infection, menstruation and hematuria. Interpretation is the responsibility of the professional caring for the patient.
Common collection and unit errors, with checklist
The most frequent error in 24-hour urine protein lies in the collection, not in the calculation. KDIGO 2024 points out that 24-hour collections have problems with completeness, storage and timing accuracy.
- Incomplete collection: one missed void reduces the volume and underestimates the result.
- Wrong time: a period longer or shorter than 24 hours changes the total; enter the actual time in the collection time field.
- Concentration unit: reports in g/L must be converted (1 g/L = 100 mg/dL); in mg/L, divide by 10 to obtain mg/dL.
- Volume in liters: 1.8 L should be entered as 1800 mL.
- Result already given in grams: 0.45 g/24h equals 450 mg/24h.
Checklist before using the number:
- Is the concentration in mg/dL and the volume in mL?
- Is the collection time entered the actual one, with no urine lost?
- Is the total urine creatinine of the collection compatible with the patient? The KDIGO equivalences assume an average creatinine excretion of about 1 g per day, a value that varies with age, sex and diet.
- Is the result close to 150 mg/24h? In that case, consider collection variability before drawing conclusions.
When 24-hour urine protein can be misleading
24-hour urine protein loses reliability when the collection does not represent the patient's usual day. Situations in which the result should be read with caution:
- Incomplete collection or one lasting other than 24 hours.
- Intense exercise, symptomatic urinary tract infection, menstruation or hematuria, which KDIGO 2024 lists as causes of increased urine protein not directly related to kidney disease.
- Children: KDIGO 2024 uses limits adjusted to body surface area, such as less than 150 mg/m² per day above 2 years of age, and not the adult cutoff that the tool applies.
- Pregnancy: proteinuria assessment follows its own obstetric criteria, which the tool does not consider.
The measurement also depends on the laboratory. KDIGO 2024 records significant variation between laboratories in the measurement of urine albumin and protein. To follow the course over time, ideally keep the same type of collection and, if possible, the same laboratory; KDIGO recommends keeping the collection method consistent throughout follow-up.
24-hour urine, protein-to-creatinine ratio and UACR
24-hour urine is not the only way to quantify protein in urine. In 1983, Ginsberg and colleagues showed, in the New England Journal of Medicine, that the protein-to-creatinine ratio in a spot sample correlates excellently with the protein in a 24-hour collection.
| Method | Sample | Unit | Strength | Limitation |
|---|---|---|---|---|
| 24-h urine protein (this calculator) | 24-h collection | mg/24h | Measures the total daily loss | Laborious and error-prone collection |
| Protein-to-creatinine ratio (UPCR) | Spot sample | mg/mg or mg/g | No timed collection needed | Depends on the patient's creatinine excretion |
| Albumin-to-creatinine ratio (UACR) | Spot sample, preferably first morning | mg/g | KDIGO's first choice for initial testing | Measures albumin only |
KDIGO 2012 approximates the categories as follows: less than 150 mg/24h of protein corresponds to a UPCR below 150 mg/g, and 150 to 500 mg/24h to a UPCR of 150 to 500 mg/g. For screening diabetic kidney disease, the guideline of the Brazilian Diabetes Society (SBD) states that 24-hour urine is not necessary and recommends UACR in a random sample. Glomerular filtration is assessed separately, for example by the eGFR by CKD-EPI.
Frequently asked questions about 24-hour urine protein
How do you calculate 24-hour urine protein?
Multiply the urine protein concentration (mg/dL) by the total collection volume (mL) and divide by 100. Example: 25 mg/dL in 1,800 mL gives 25 × 18 = 450 mg/24h.
What is the reference value for 24-hour urine protein?
KDIGO classifies protein excretion as A1 (below 150 mg/24h, normal to mildly increased), A2 (150 to 500 mg/24h, moderately increased) and A3 (above 500 mg/24h, severely increased). The calculator uses these ranges.
The report came in g/24h or the concentration in g/L. How do I convert?
For the result, multiply g/24h by 1,000: 0.45 g/24h is 450 mg/24h. For the concentration, multiply g/L by 100 to obtain mg/dL before using the calculator.
The collection did not last exactly 24 hours. Does the calculator correct for that?
Yes. Enter the actual collection time, up to 48 hours, and the tool converts the total to 24 hours. An incomplete collection, however, still underestimates the result: the conversion does not correct for missed voids.
Does the protein-to-creatinine ratio replace 24-hour urine?
For initial testing, KDIGO prefers spot-sample ratios, such as UACR and UPCR, which correlate well with the 24-hour collection. 24-hour urine remains useful when the total daily loss needs to be measured.
References
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int. 2024;105(4S):S117-S314. doi:10.1016/j.kint.2023.10.018. View
- Kidney Disease: Improving Global Outcomes (KDIGO) CKD Work Group. KDIGO 2012 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. Kidney Int Suppl. 2013;3(1):1-150. View
- Ginsberg JM, Chang BS, Matarese RA, Garella S. Use of single voided urine samples to estimate quantitative proteinuria. N Engl J Med. 1983;309(25):1543-6. doi:10.1056/NEJM198312223092503. View
- Sá JR, Canani LH, Rangel EB, Bauer AC, Escott GM, Zelmanovitz T, et al. Avaliação e tratamento da doença renal do diabetes. Diretriz Oficial da Sociedade Brasileira de Diabetes. 2024. doi:10.29327/5412848.2024-6. View
- Kidney Disease: Improving Global Outcomes (KDIGO) Glomerular Diseases Work Group. KDIGO 2021 Clinical Practice Guideline for the Management of Glomerular Diseases. Kidney Int. 2021;100(4S):S1-S276. View
Updated . A support tool for educational purposes; it does not replace clinical assessment.