Introduction

A 24-hour urinalysis is a timed urine collection used for evaluating urinary stone disease, proteinuria (eg, amyloidosis, lupus nephritis, nephrotic syndrome, and preeclampsia), multiple myeloma, pheochromocytoma (fractionated metanephrines and catecholamines), and renal function through urea and creatinine clearance. This test is usually conducted in an outpatient setting while the patient maintains their usual diet. Results are analyzed alongside detailed medical and dietary history, serum chemistry, and stone composition (if available) to assist in diagnosis and guide therapy or prophylactic treatment. Further, this urine study can be used in pediatrics to test for inherited conditions such as primary hyperoxaluria and cystinuria.[1][2] Pheochromocytomas and paragangliomas, which are rare conditions causing catecholamine excess, are diagnosed in symptomatic individuals through elevated urine and plasma metanephrines. The collection procedure is similar to other conditions; however, the data must be interpreted cautiously due to the very low pretest probability.[3]

Current laboratory values estimate the glomerular filtration rate (GFR) based on creatinine levels. However, these estimates can vary significantly from the true GFR if creatinine levels are unstable or for other reasons. Therefore, a 24-hour urine collection can be a valuable tool in evaluating abnormal renal function, but adherence to proper collection techniques is essential, as is educating the patient about the strict guidelines for a 24-hour collection. Shorter urine collections, such as 8- or 12-hour, can improve patient adherence and accuracy in specimen collection. However, 24-hour collections are generally preferred because they account for daily creatinine variations and solute excretion.

Etiology and Epidemiology

Nephrolithiasis is a prevalent condition, affecting 10% to 11% of the global population. Kidney stones are more common in men than women, and incidence varies by geographic location. Nephrolithiasis is increasing globally each year due to rising risk factors, particularly high-animal protein and high-salt diets, diabetes, metabolic syndrome, and obesity. Please see StatPearls' companion resource, "Renal Calculi, Nephrolithiasis," for more information. The incidence of chronic kidney disease (CKD) has also been increasing worldwide. Determining the true incidence and prevalence of CKD is challenging due to the asymptomatic nature of early to moderate stages. Globally, CKD accounted for 2,968,600 (1%) disability-adjusted life-years and 2,546,700 (1%-3%) life-years lost in 2012.[4] The rising incidence of CKD is due to increased risk factors such as diabetes and hypertension, as well as longer life expectancies, as GFR naturally declines with age. Please see StatPearls' companion resource, "Chronic Kidney Disease," for more information.

Pheochromocytomas originate from the chromaffin cells of the adrenal medulla, and their clinical manifestations result from excess catecholamine release. Paragangliomas arise from extra-adrenal chromaffin cells in the sympathetic or parasympathetic nervous system. While paragangliomas are not always symptomatic, they typically present with symptoms related to catecholamine excess when they do. Additionally, paragangliomas can cause symptoms based on their location, mass effect, or bony erosions. Paragangliomas and pheochromocytomas are often grouped together for statistical purposes, with a combined incidence estimated at 0.7 to 1.0 cases per 100,000 person-years. Another review found that 0.3% of patients tested for secondary hypertension were diagnosed with pheochromocytoma.[5] Thus, even among patients at higher risk for pheochromocytoma, the incidence remains very low outside of inherited endocrine disorders such as multiple endocrine neoplasia type 2, neurofibromatosis type I, or von Hippel-Lindau syndrome. Please see StatPearls' companion resources, "Pheochromocytoma" and "Paraganglioma," for more information.[6][7]

Pathophysiology

Catecholamines are rapidly inactivated by the catechol-O-methyltransferase, converting them into metanephrine and normetanephrine, which are then conjugated with sulfate. These compounds have a long half-life and are excreted in the urine, making them more suitable for measurement than catecholamines. Elevated plasma metanephrines are considered more specific than elevated urine metanephrines. Additionally, the level of increased metanephrine correlates with tumor size. Please see StatPearls' companion resources, "Renal Calculi, Nephrolithiasis" and "Chronic Kidney Disease," for details on the pathophysiology of nephrolithiasis and CKD.

The European Society of Clinical Practice Guidelines recommend using liquid chromatography with mass spectrometry or electrochemical detection methods over other techniques. Literature reports that urine metanephrines' sensitivity ranges from 86% to 97%, while specificity ranges from 69% to 95%.[7] A key consideration is that, due to the frequent testing and the low prevalence of true pheochromocytoma and paraganglioma, false positives significantly outnumber true positives.[8][9] Please see StatPearls' companion resource, "Pheochromocytoma," for more information.

Specimen Requirements and Procedure

Specific instructions for collecting a 24-hour urine sample may vary by laboratory. Typically, the patient's first voided morning urine sample is discarded. Subsequent urine over the next 24 hours, including the first void of the next morning, is collected in containers that the laboratory provides. For example, if the urine specimen collection begins at 9 am, the patient would void into the toilet at 9 am, collect all urine in the specimen bottle for the next 24 hours, and include the 9 am void the following day. The sample should be refrigerated throughout the collection period.

A preservative solution is added to the urine collection to stabilize the sample for later analysis. After the full 24-hour collection, the total volume is recorded, and a representative sample is submitted to the laboratory for analysis. Proper patient education on collection procedures is crucial for ensuring the accuracy of the 24-hour urine sample.[10] The evaluation often includes serum samples for creatinine, urea, calcium, potassium, uric acid, and phosphorus. Patients are typically advised to follow their usual diet and activities during the collection period.[11][12]

After analysis, a detailed report of the results is provided to the ordering clinician. Collecting a 24-hour urine sample can be challenging and inconvenient for some patients. As mentioned, if a full 24-hour collection is not feasible, a shorter collection can be used, provided the instructions are followed carefully and the time is precisely recorded. Accurate results reliably identify urinary chemistry risk factors for calculus formation and can aid in diagnosing other medical conditions, as spot urine chemistry is often insufficient. For kidney stone prevention, a properly collected 24-hour urine analysis is as valuable as analyzing the chemical composition of the stone itself. Please see StatPearls' companion resource, "24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines," for more information.

For pheochromocytoma (metanephrine) urine testing, it is recommended that patients avoid food, caffeine, smoking, and strenuous exercise for 8 to 12 hours before sample collection. Many medications can interfere with metanephrine levels, leading to false positives. Drugs such as acetaminophen, tricyclic antidepressants (eg, amitriptyline), serotonin-norepinephrine reuptake inhibitors (eg, buspirone), alpha-blockers (eg, tamsulosin), haloperidol, labetalol, levodopa, lamotrigine, aripiprazole, and possibly selective serotonin reuptake inhibitors can elevate plasma and urine metanephrines. Notably, it is estimated that drug interference causes up to 20% of false-positive results, with tricyclic antidepressants and the alpha-blocker phenoxybenzamine accounting for up to 45% of these cases. Therefore, when possible, these medications should be discontinued 10 to 14 days before testing.[8][13]

Diagnostic Tests

Various laboratories offer 24-hour urine testing, providing clinicians with detailed reports that stratify stone risk based on laboratory data. Typically, 24-hour urine tests for nephrolithiasis evaluation include measurements of urinary volume, pH, calcium, citrate, magnesium, phosphate, sulfate, oxalate, and uric acid. Supersaturation ratios for different stone types can then be calculated. In patients with a history of cystine stones or a positive cystine cyanide test, 24-hour cystine levels can also be assessed.[14][15]

Finding or selecting a laboratory to process 24-hour urine chemistries can be challenging. Ideally, all tests should be completed at a single laboratory, and the results should be presented clearly, including both 24-hour totals and relative concentrations. While normal values provide a baseline, they may not represent "optimal" values for patients with nephrolithiasis. Therefore, normal urinary chemistry reference values for each lab should be reported alongside the results.

Testing Procedures

The primary techniques for evaluating serum, plasma, and urine creatinine levels include enzymatic assays, colorimetric assays using alkaline picrate, and high-performance liquid chromatography. Colorimetric and enzymatic assays are also commonly used to measure urea concentration. Most of these methods use urease and a coupled enzyme that utilizes ammonia as a substrate.[16] Proteins are usually measured using mass spectrometry coupled with liquid chromatography. Less commonly, antibodies or deoxyribonucleic aptamers are used to bind specific proteins. Detecting posttranslational modifications can be more challenging; methods such as colorimetric assays, radioactive isotope-labeled substrates, Western blotting with protein-specific antibodies, and peptide and protein arrays are also used.[17] Plasma and urine metanephrines are metabolites of epinephrine and norepinephrine. Metanephrines are relatively stable compared to catecholamines and can be stored at 4 °C for up to 3 days without significant degradation. For testing delays longer than 3 days, storing samples at -20 °C or lower is recommended.[6]

Interfering Factors

The amount of creatinine produced daily depends on muscle mass. As CKD progresses, muscle mass tends to decline, which affects creatinine production. Therefore, creatinine reference ranges vary between sexes, with lower values typically seen in children and individuals with reduced muscle mass. Dietary factors also influence creatinine levels; for instance, consumption of red meat can alter creatinine by up to 30%.

In addition, some patients, particularly young males, may use creatine supplements to increase muscle mass, so it is important to inquire directly about this.[18] During pregnancy, GFR increases, resulting in lower creatinine levels. This factor should be considered when interpreting creatinine measurements in pregnant women. One limitation of using creatinine formulas to estimate GFR is that serum creatinine levels may not reflect renal impairment until it has advanced significantly. In some studies, renal function can decrease by up to 50% before a rise in serum creatinine is detected.[19] Medications commonly affecting urine metanephrine levels are listed in the Specimen Requirements and Procedure section.

Results, Reporting, and Critical Findings

The components of 24-hour urine tests vary by laboratory, but standard analyses typically include urine volume, calcium, oxalate, citrate, uric acid concentrations, pH levels, and supersaturation values. Supersaturation levels for calcium oxalate, calcium phosphate, and uric acid are commonly reported. Additional analytes may include sodium, potassium, magnesium, phosphorus, ammonium, chloride, sulfate, and nitrogen (in the form of urea). Reports usually provide reference range values to help assess the risk of stone formation.

Specialized testing is available for pediatric individuals and those with cystinuria, which includes measuring cystine excretion, supersaturation, and urine pH. Since urine chemistry is a continuous variable, strict cut-off points for abnormal values are somewhat arbitrary. As urinary constituents deviate from normal or optimal ranges, the risk of stone formation increases. Below is a summary of the key components of the 24-hour urinalysis and their clinical significance. Please see StatPearls' companion resource, "24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines," for more information.

Light-Chain Proteinuria

Light chains, such as Bence-Jones proteins, are used as markers for conditions such as multiple myeloma, amyloidosis, and other monoclonal gammopathies affecting the kidneys. Under normal circumstances, these proteins are undetectable in urine, so any positive finding in a 24-hour urine collection is considered abnormal. Please see StatPearls' companion resources, "Bence-Jones Protein" and "Multiple Myeloma," for more information.

Calcium

Elevated urinary calcium levels are found in over a third of patients with calcific stones. Urine calcium concentration is influenced by dietary calcium, sodium, and protein intake, medical comorbidities, kidney function, hormonal influences, and, in some cases, genetic conditions. A moderate calcium intake is recommended to limit excessive urinary calcium excretion, support bone health, and prevent increased oxalate absorption due to reduced intestinal oxalate binding. A very low calcium diet reduces the intestinal binding of oxalate, leading to increased oxalate absorption and hyperoxaluria, which significantly promotes calcium oxalate nephrolithiasis formation. Please see StatPearls' companion resource, "24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines," for more information. Depending on the underlying etiology, urinary calcium modulation is typically achieved through dietary adjustments or medications such as thiazides. Optimal urinary calcium levels are generally below 250 mg/d or 150 mg/L of urine. Please see StatPearls' companion resource, "Hypercalciuria," for more information.

Citrate

Citrate is a potent urinary inhibitor of calcium salt crystallization and acts as a urinary alkalinizing agent. Hypocitraturia, a common risk factor for kidney stones, occurs in up to one-third of calcium stone formers. Low urinary citrate levels may result from dietary factors, metabolic acidosis, or hypokalemia, though it can also be idiopathic. Citrate is present in citrus juices such as grapefruit, orange, lemon, and lime. However, most patients with low urinary citrate levels typically require supplementation, often in potassium citrate, as dietary intake alone is usually insufficient to correct the deficiency.

Concentrated citrate supplements, such as potassium citrate, are available in tablet and liquid forms. Lower potassium alternatives are also offered, and sodium bicarbonate may be used. Optimal urinary citrate levels are approximately 300 mg/1000 mL of urine or around 600 mg daily. Higher doses may be necessary if the therapy aims to increase urinary pH, especially in cases of pure uric acid urolithiasis, where optimizing urinary pH is crucial. Please see StatPearls' companion resource, "Uric Acid Nephrolithiasis," for more information. Overalkalinization of the urine can predispose patients to calcium phosphate stone production, particularly if the pH consistently exceeds 7.0. Low urinary citrate levels may also contribute to persistent calcium-based stones in some patients, even when hydrochlorothiazide is used. Please see StatPearls' companion resource, "Hypocitraturia and Renal Calculi," for more information. 

Magnesium

Magnesium plays a role in inhibiting urinary crystallization, reducing the risk of stone formation. Approximately half of dietary magnesium is excreted in the urine, so low urinary magnesium levels are often due to inadequate dietary intake. A urinary magnesium level below 24 mg/d is generally considered abnormally low.

Metanephrines and Catecholamines

Pheochromocytomas and paragangliomas can produce elevated levels of metanephrines and catecholamines, leading to hypertension. Rarely, neuroblastomas may also cause increased levels. Fractionated metanephrines are generally preferred for diagnosis, but catecholamines and vanillylmandelic acid measurements can also be useful.

Each reference laboratory will have its own specified normal ranges, but in general, normal 24-hour urine levels would include the following:

• Dopamine: Up to 400 mcg
• Epinephrine: Up to 20 mcg
• Norepinephrine: Less than 100 mcg
• Normetanephrine: Less than 350 mcg
• Total catecholamines: Less than 100 mcg
• Total metanephrines: Less than 400 mcg
• Vanillylmandelic acid: Less than 7 mg

Please see StatPearls' companion resources, "Pheochromocytoma," "Paraganglioma," and "Physiology, Catecholamines," for more information.

Nephrotic Syndrome

Nephrotic syndrome is defined by a 24-hour urinary protein excretion of 3 g or more in adults (or 40 mg/h/m² in children). However, a spot urine sample is much easier to obtain and can be a reasonable screening test. In a spot urine sample, a protein-to-creatinine ratio of 2 or higher (2 g of protein per gram of creatinine) suggests nephrotic syndrome but should be confirmed with a 24-hour urine test. Additionally, urine sediment may reveal casts upon microscopic examination.

An underlying cause, such as a long history of clinically significant diabetes with related complications, may be evident. If diabetes has persisted for 5 years or more and diabetic neuropathy is present, diabetic nephropathy is a likely cause. If no clear underlying cause is identified, a renal biopsy may be necessary for a definitive diagnosis. The likely issue is damage to the renal glomerular basement membrane. However, as treatment approaches differ, a biopsy is crucial to differentiate between minimal-change disease, focal segmental glomerulosclerosis, and membranous nephropathy.

Besides intrinsic renal disease, other potential causes include acute postinfectious nephritis, Alport syndrome, amyloidosis, immunoglobulin A nephropathy, diabetes, infections (such as cytomegalovirus, hepatitis, and human immunodeficiency virus), medications (eg, nonsteroidal anti-inflammatory drugs), preeclampsia, systemic lupus erythematosus, and thrombotic microangiopathy.[20] Treatment depends on the underlying etiology. Please see StatPearls' companion resources, "Nephrotic Syndrome," "IgA Nephropathy (Berger Disease)," "Goodpasture Syndrome," "Amyloidosis," "Preeclampsia," "Systemic Lupus Erythematosus," "Glomerulonephritis," and "Alport Syndrome," for more information.

Oxalate

Elevated urinary oxalate is a common finding in patients with calcium-based stones, with approximately one-third of these individuals showing increased levels. Oxalate can be both endogenous and dietary; dietary oxalate is absorbed primarily in the colon and distal ileum. Normal oxalate excretion typically ranges from 40 to 50 mg/d, with 40 mg being a commonly accepted upper limit of normal. For managing stone formation, goals for oxalate reduction often aim for "optimal" levels of 25 mg/d or lower.

Dietary sources of oxalate include black tea, nuts, chocolate, and green leafy vegetables such as spinach. Excessive vitamin C supplements can also be metabolized to oxalate in the urine, so limiting vitamin C intake to 1000 mg or less daily is advisable. Enteric hyperoxaluria, which can significantly increase the risk of stone formation, is associated with conditions such as inflammatory bowel disease, cystic fibrosis, pancreatic insufficiency, or previous bariatric bowel surgery. In addition to dietary adjustments, using intestinal oxalate binders like calcium citrate (without vitamin D) can help reduce oxalate absorption. Please see StatPearls' companion resource, "Hyperoxaluria," for more information.

pH

Human urine typically has a pH between 4.5 and 8.0. Urine pH is crucial because variations can influence the crystallization of specific salts. The crystallization of calcium phosphate, calcium oxalate, uric acid, cystine, and struvite stones depends on pH. While calcium oxalate precipitation is less pH-dependent than others, it generally occurs in acidic urine. Uric acid stones are most likely to form when urine pH is below 5.5, whereas calcium phosphate crystals tend to form in a more alkaline environment with a pH of 6.5 or above. Ideally, the average urine pH over 24 hours should be between 5.7 and 6.3 to minimize the risk of pH-dependent stone formation. Urinary pH can be adjusted through treatments such as potassium citrate and sodium bicarbonate, but it can also be affected by other medications, such as acetazolamide. Please see StatPearls' companion resource, "Acetazolamide," for more information.

Proteinuria

About half of proteinuria is composed of uromodulin (Tamm-Horsfall protein), so urine albumin-to-creatinine ratios are often used to quantify abnormal urinary protein levels. Albumin excretion of more than 30 mg/24 hours is considered abnormal. Albumin levels of 30 to 300 mg per 24 hours are classified as stage 2 albuminuria (A2 or microalbuminuria). Albumin levels exceeding 300 mg per 24 hours are classified as stage 3 albuminuria (A3 or macroalbuminuria) (see Table. The National Kidney Foundation Albuminuria below).

Table. The National Kidney Foundation Albuminuria Staging

ACR, albumin-to-creatinine ratio.

*Relative to levels in young adults. **Including nephrotic syndrome (albumin excretion ACR >2220 mg/g)

If amyloidosis or monoclonal gammopathy is suspected, measuring 24-hour urine light chains (Bence-Jones protein) is recommended. While a high correlation exists between urine protein-to-creatinine ratio and albuminuria, the correlation with urinary light chains is only moderate.[21] Protein levels of 3 g or more in 24 hours are indicative of nephrotic syndrome, as discussed above. Please see StatPearls' companion resources, "Microalbuminuria" and "Proteinuria," for further information.[43]

Sodium and Potassium

Urinary sodium excretion generally reflects dietary sodium intake. Increased urinary sodium excretion correlates with increased calcium excretion, making dietary sodium control crucial for managing hypercalciuria. Typically, lower-sodium diets permit up to 1500 mg of dietary sodium daily. Urinary potassium concentration is useful for assessing compliance with treatments like potassium citrate; these supplements should significantly increase urinary potassium levels.

Uric Acid

Uric acid, a byproduct of purine metabolism, is influenced by high-purine foods such as alcohol, anchovies, bacon, beef, herring, lamb, liver, mackerel, organ meats, sardines, and scallops. Elevated levels may also result from metabolic liver conditions, gout, or uricosuric medications such as probenecid, which increase urinary uric acid excretion. High urinary uric acid (hyperuricosuria) predisposes the affected patient by increasing the risk of calcium urolithiasis and uric acid stones. However, most pure uric acid stones are primarily due to acidic urine rather than excess urinary uric acid levels. Additionally, uric acid nephrolithiasis is strongly associated with metabolic syndrome.

Patients with uric acid nephrolithiasis are generally treated with urinary alkalinization therapy, such as potassium citrate, aiming for an optimal urine pH of 6.5 to 7. For hyperuricosuric patients who develop calcium-based stones, allopurinol is recommended to lower urinary uric acid levels to 600 mg daily or less. Please see the StatPearls' companion resources, "Uric Acid Nephrolithiasis," "Hyperuricosuria," and "24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines," for more information.[28]

Urine Volume and Creatinine

Decreased urine volume is a significant risk factor for stone disease, as concentrated urine increases the supersaturation of stone-forming salts. A 1999 prospective trial by Borghi et al provided results showing that an optimal urinary volume of 2500 mL/d can help reduce stone risk.[22] While increasing urine volume beyond this level may further lower the risk, achieving such high volumes can be challenging and may lead to frequent urination, which some patients find bothersome. Urine creatinine excretion helps assess the accuracy of a timed urine collection. As a byproduct of muscle metabolism, creatinine excretion remains relatively stable based on muscle mass. The average daily creatinine excretion is 18 to 25 mg/kg for males and 15 to 20 mg/kg for females. A lower-than-expected creatinine excretion value typically indicates an incomplete collection. Creatinine clearance, described in the next section, provides further insights into kidney function.

Clinical Significance

Measurement of Renal Function (Creatinine Clearance)

Numerous formulas are available to estimate renal function, with most relying on creatinine levels. The Chronic Kidney Disease Epidemiology Collaboration, CKD-EPI equation, is currently the most commonly used formula in laboratories and hospitals. This formula estimates the GFR using creatinine levels and sex as critical variables.[23] The gold standard for GFR is injecting inulin and measuring kidney clearance.[24] However, this method is invasive, time-consuming, and unavailable in all laboratories. As an alternative, the biochemical marker creatinine in serum and urine is commonly used to estimate GFR.[25] Please see StatPearls' companion resource, "Renal Function Tests," for further information.

Creatinine is the anhydride product of creatinine and is directly related to muscle mass.[10] Creatinine clearance (CrCl) is the volume of blood plasma cleared of creatinine per unit time and provides a rapid, cost-effective method for assessing renal function. CrCl and GFR can be estimated using urine creatinine, serum creatinine, and urine volume collected over a specific period. However, because the peritubular capillaries secrete creatinine, CrCl tends to overestimate GFR by about 10% to 20%. Despite this margin of error, CrCl remains an accepted method for measuring GFR due to its ease of measurement.[26]

CrCl is calculated using the equation:

• Cr_Cl= (U_Cr × V) / P_Cr

Cr_Cl = creatinine clearance; U_Cr= urinary creatinine concentration (mg/dL); V= urinary flow rate (volume/time in mL/min); and P_Cr= plasma creatinine concentration (mg/dL).

Urea clearance, similar to creatinine clearance, is used to estimate renal function:

• Cl_ur= (U_ur × V) / P_ur

Cl_ur= urea clearance; U_ur= urinary urea concentration (mg/dL); V= urinary flow rate (volume/time in mL/min); and P_ur= plasma urea concentration (mg/dL).

Please see StatPearls' companion resource, "Renal Function Tests," for further information.

Nephrolithiasis Prevention

The 24-hour urinalysis is a key component of the metabolic workup for individuals with recurrent nephrolithiasis. Accurate collections can identify treatable abnormalities predisposing individuals to stone formation and help monitor treatment effectiveness. Since urinary constituents can vary significantly based on diet and lifestyle, their interpretation can be complex and often subjective. More than 90% of patients with kidney stones will exhibit at least 1 suboptimal chemical disorder. While 24-hour urine testing alone does not cure nephrolithiasis, it helps guide effective prophylactic treatment for patients committed to adhering to long-term therapeutic guidelines. Please see StatPearls' companion resource, "24-Hour Urine Testing for Nephrolithiasis: Interpretation and Treatment Guidelines," for a more detailed guide to interpreting 24-hour urine testing for kidney stone prophylaxis analysis and therapy. According to the American Urological Association guidelines, 24-hour urine testing should be offered to all patients with nephrolithiasis, regardless of symptoms. This is especially recommended for pediatric and high-risk individuals and those highly motivated to adhere to long-term prophylactic treatment recommendations.[27][28][29][30]

Quality Control and Lab Safety

Nomograms for creatinine excretion based on age, weight, sex, and sometimes ethnicity have been developed to compare expected creatinine levels in 24-hour samples, helping to assess sample validity.[10][19][21] If the sample differs by more than 30% from the expected value, it likely indicates over-collection, under-collection, or the presence of an interfering factor.[10] While expected creatinine values vary, a commonly used threshold is that less than 15 mg/kg for women and less than 20 mg/kg for men in a 24-hour collection suggests under-collection. Another validation method compares expected creatinine values with muscle mass measured by bioimpedance, as muscle mass strongly correlates with creatinine levels. However, this test is not commonly performed.[21] One formula used to calculate the expected 24-hour urine creatinine, as derived by Gerber et al, is as follows: 

Estimated 24-hour creatinine excretion (mg/24h)= 699 - 421.9 (if female) + (7.64 × weight [in pounds]) - 25.82 (if White) - (2.67 × age [in years]).[21][31]

Urine protein-to-creatinine ratios can also be used to estimate proteinuria collected in a 24-hour urine collection. As approximately half of the proteinuria consists of uromodulin (Tamm-Horsfall protein), urine albumin-to-creatinine ratios are often preferred to quantify abnormal urinary protein. Please see StatPearls' companion resources, "Microalbuminuria" and "Proteinuria," for further information.[43]

Enhancing Healthcare Team Outcomes

A 24-hour urinalysis is a timed urine collection used to evaluate the metabolic status of various kidney disorders and accurately quantify GFR and proteinuria. For inpatients, nurses typically collect the urine and must ensure it remains free from contaminants. In outpatient settings, patients need proper education on how to collect the urine sample accurately. Precise collections can identify treatable abnormalities that predispose to nephrolithiasis, assist in diagnosing conditions such as pheochromocytoma, and provide accurate measurements for monitoring the progression of CKD.

Effective communication among healthcare team members is paramount. Primary care clinicians and hospitalists often identify renal abnormalities first and may refer patients to pediatric or adult nephrologists. Patients with significant nephrolithiasis should be offered 24-hour urine testing for stone prophylaxis therapy and should be referred to urology. Clinicians and nurses must ensure that patients are fully informed about the procedures and requirements for 24-hour urine collection, with clear, written instructions provided to support patient understanding. Laboratory staff should ensure proper specimen handling and processing. Clear communication across the healthcare team facilitates timely diagnosis and treatment decisions, enabling a coordinated response and the effective use of clinical data.