Spot Urine Protein-to-Creatinine Ratio Calculator (UPCR / PCR)
Calculate a same-specimen spot urine total protein-to-creatinine ratio in mg/mg, mg/g, and mg/mmol; not ACR, 24-hour protein, or a diagnosis.
Content updated: View sources
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Formula and medical content are based on the references listed on this page. See sources, About, and Sources and Review Process.
About
This page calculates the spot urine total-protein-to-creatinine ratio (UPCR or PCR) from total protein and creatinine measured in the same spot or untimed specimen. It reports mg/mg, mg/g, and mg/mmol: three unit expressions of one ratio, not three different tests. It measures total protein rather than albumin. [1, 4]
The ratio partly reduces the effect of urine concentration or dilution, but it still depends on individual creatinine excretion. Muscle mass, body size, acute kidney injury, diet, exercise, and other factors can change the relationship between a spot ratio and timed protein excretion. This page does not convert UPCR into mg/day or a 24-hour excretion value. [1, 4]
ACR is generally preferred for initial detection of lower-level proteinuria in CKD because it measures albumin specifically. PCR answers a total-protein question and may include albumin and non-albumin proteins; it cannot calculate the albumin fraction or assign A1, A2, or A3. One PCR result cannot diagnose CKD or nephrotic syndrome or determine treatment. [1, 2]
Formula
Interpretation
| Quantity | What it represents | Calculated here |
|---|---|---|
| Urine total protein concentration | Laboratory protein concentration in the submitted specimen | Input |
| Urine creatinine concentration | Laboratory creatinine concentration in the same specimen | Input |
| UPCR mg/mg | Total protein mass divided by creatinine mass | Yes |
| UPCR mg/g | The same ratio expressed per gram creatinine | Yes |
| UPCR mg/mmol | The same ratio expressed per mmol creatinine | Yes |
| UACR / ACR | Urine albumin divided by creatinine | No |
| Timed protein excretion | Protein collected over a defined time, such as 24 hours | No |
The three UPCR outputs are unit expressions of one ratio and are not separate clinical tests. ACR requires a urine albumin result, and daily excretion requires timed collection information. This page does not turn a ratio into a diagnosis, stage, or treatment.
What this calculator computes
The calculator separately normalizes submitted total urine protein and same-specimen urine creatinine, calculates one ratio at full precision, and displays it in mg/mg, mg/g, and mg/mmol. It does not read or infer urine albumin, urine volume, collection duration, or daily creatinine excretion.
Why the same specimen matters
Protein and creatinine must describe the same urine dilution state: use values from one container and one void, not different dates, specimens, or laboratories. Editing either value or changing a unit clears the confirmation and old result as a software safety measure.
First-morning versus random spot specimens
KDIGO generally prefers a first-morning midstream sample because biological variability is lower; a random spot sample may be used when a first-morning sample is unavailable. Follow the applicable laboratory and clinical pathway. Ginsberg 1983 was a historical study in stable adults and does not establish sampling quality for every modern population. This page cannot verify how a specimen was collected. [1, 3]
UPCR versus ACR
UPCR measures total protein; ACR measures albumin. KDIGO and NICE generally prefer ACR for initial lower-level CKD proteinuria testing because it is more sensitive to albumin. PCR may address total protein or suspected non-albumin protein, but it cannot be converted into ACR or assign A1/A2/A3. [1, 2]
Total protein and non-albumin proteins
Spot ratio versus timed urine protein
Spot PCR can correlate with timed protein excretion in some stable populations, but that relationship is not an exact individual conversion. High proteinuria, changing kidney function, collection error, and differences in creatinine excretion can reduce agreement. This page intentionally provides no mg/day or 24-hour estimate. [3, 4]
Units, conversion, precision, and display
Protein follows mg/dL × 10 or g/L × 1000 to mg/L. Creatinine mass units use the same mass paths; mmol/L uses the fixed software factor 113 mg/mmol. Intermediate arithmetic is not rounded. mg/mg displays four decimals; mg/g and mg/mmol display one. True zero protein remains zero, and tiny positive results do not display as false zero. These software input limits are not laboratory reference intervals.
Worked examples from the implementation
50 mg/dL protein and 100 mg/dL creatinine: 500 mg/L protein and 1000 mg/L creatinine (8.849557522123893 mmol/L) produce 0.5000 mg/mg, 500.0 mg/g, and 56.5 mg/mmol.
500 mg/L and 1000 mg/L: the same physical concentrations reproduce 0.5000 mg/mg, 500.0 mg/g, and 56.5 mg/mmol.
0.5 g/L and 1 g/L: mass-unit normalization reproduces the same three displays.
500 mg/L protein and 8.849557522123893 mmol/L creatinine: the amount-concentration path normalizes to the same values and displays.
0 mg/L protein and 1000 mg/L creatinine: the arithmetic is 0.0000 mg/mg, 0.0 mg/g, and 0.0 mg/mmol. This does not prove the absence of kidney disease or another urine abnormality.
These examples audit implementation, units, and display behavior. They are not patient diagnoses or 24-hour excretion estimates.
Historical study observations without dynamic categories
In a stable-adult 1983 study, values below 0.2 mg/mg were associated with the study's normal-range observation and values above 3.5 mg/mg with nephrotic-range proteinuria. These are historical study context, not universal live categories. The calculator does not label results normal, abnormal, or nephrotic, and nephrotic-range proteinuria is not the same as nephrotic syndrome. [3, 4]
Creatinine excretion and ratio bias
Lower urine creatinine excretion can make a ratio relatively higher, while higher excretion can make it relatively lower. Muscle mass, body size, biological sex-related physiology, diet, exercise, and AKI can affect creatinine. A ratio reduces but does not remove urine and person-level variability, and this page makes no demographic correction. [1, 4]
Transient and preanalytical factors
Hematuria, menstruation, recent exercise, symptomatic UTI, acute illness, AKI, contamination, collection timing, changing treatment, extreme dilution or concentration, and mismatched specimens can affect interpretation. One ratio cannot distinguish persistent from transient change. [1]
Laboratory method and assay variation
Total-protein assays may respond differently to different proteins, and creatinine method or calibration can also affect the ratio. Small differences between laboratories or methods are not necessarily biological change. Trend comparisons are clearest when laboratory, method, units, and collection conditions remain consistent. This page does not validate an analyzer or assay. [4]
Pregnancy and pediatric pathways are separate
General CKD sampling guidance cannot be automatically applied in pregnancy. NICE's hypertension-in-pregnancy pathway uses PCR but specifically says not to use a first-morning void for that assessment. This page does not diagnose preeclampsia or select obstetric management. Pediatric interpretation is likewise age-, cause-, and pathway-specific; the calculator supplies arithmetic without pregnancy or pediatric categories. [1, 6]
What the result cannot determine
The result cannot determine albumin fraction, A1/A2/A3, CKD diagnosis or stage, daily protein excretion, nephrotic syndrome, cause of proteinuria, biopsy, referral, pregnancy diagnosis, pediatric management, medicine, or treatment.
References
- KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease.
- NICE NG203. Chronic kidney disease: assessment and management. Recommendations 1.1.10–1.1.14.
- 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):1543–1546. PMID 6656849. DOI 10.1056/NEJM198312223092503.
- Kamińska J, et al. Diagnostic utility of protein to creatinine ratio in spot urine within routine clinical practice. Crit Rev Clin Lab Sci. 2020;57(5):345–364. PMID 32058809. DOI 10.1080/10408363.2020.1723487.
- NIH PubChem. Creatinine, CID 588. Molecular weight approximately 113.12 g/mol.
- NICE NG133. Hypertension in pregnancy: diagnosis and management. Assessment of proteinuria in hypertensive disorders of pregnancy.
FAQ
They are unit expressions of the same protein-to-creatinine ratio. mg/mg is numerically equivalent to g/g. This implementation uses the fixed 113 mg/mmol creatinine factor, so mg/mmol = mg/g × 0.113.
Sources: [5]
KDIGO generally prefers a first-morning midstream specimen because biological variability is lower, while a random spot may be used when it is unavailable. The applicable pathway matters: NICE specifically advises against a first-morning void for proteinuria assessment in hypertensive pregnancy.
Hematuria, menstruation, exercise, symptomatic urinary infection, acute kidney injury, urine concentration, diet, muscle mass, body size, and collection conditions can affect protein or creatinine. Low creatinine excretion can relatively raise PCR, while high excretion can relatively lower it.
The implementation uses a fixed rounded conversion of 1 mmol creatinine = 113 mg, corresponding to creatinine's molecular weight of approximately 113.12 g/mol. It is a software conversion convention, not an infinitely precise natural constant or a serum-creatinine conversion.
Sources: [5]
Not necessarily. Total-protein assays can respond differently to different proteins, and protein and creatinine method, calibration, interference, and reporting practice can affect comparison. This page cannot validate an assay or infer protein composition.
Sources: [4]
Protein and creatinine are first normalized in their reported units. PCR mg/mmol = protein mg/L ÷ creatinine mmol/L; mg/g = mg/mmol ÷ 0.113; and mg/mg = mg/g ÷ 1000. Intermediate arithmetic is not rounded.
Sources: [5]
No. Pregnancy thresholds, timing, sampling, and clinical criteria belong to a separate obstetric pathway; NICE specifically advises against a first-morning void in that assessment. This page does not diagnose or exclude preeclampsia or select monitoring or treatment.
Sources: [6]
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Disclaimer
Educational and informational reference only. Not intended to replace professional medical advice, diagnosis, treatment, or independent verification.