Nephron physiology explains findings such as glucose in the urine with a normal blood glucose, or red blood cell (RBC) casts with a rising creatinine. The nephron introduction connects filtration, reabsorption, and secretion with urine findings. These mechanisms also explain renal function tests and the patterns of glomerular, tubular, and metabolic disease.
From nephron to urine
Review the nephron pathway and segment table before the more detailed physiology below.
Glomerular filtration
The filtration barrier consists of fenestrated endothelium, the glomerular basement membrane, and podocyte foot processes with slit diaphragms. Barrier structure and molecular size strongly limit albumin passage. Hydrostatic pressure within glomerular capillaries drives filtration against the pressure in Bowman space and the oncotic pressure of retained plasma proteins.
Afferent arteriolar myogenic tone and tubuloglomerular feedback help stabilize renal blood flow and glomerular filtration rate (GFR). During reduced renal perfusion, renin release activates the renin-angiotensin-aldosterone system. Angiotensin II preferentially constricts the efferent arteriole and promotes sodium and water conservation through aldosterone and vasopressin pathways. These responses can preserve filtration pressure for a time. Severe or sustained hypoperfusion lowers GFR.1,3
Reabsorption, concentration, and secretion
The proximal tubule reabsorbs most of the filtered water and sodium along with nearly all filtered glucose and amino acids under ordinary conditions. A transport maximum is the highest rate at which a carrier system can transport a substance. A renal threshold is the plasma concentration at which that substance begins to appear in urine. Glucose commonly begins to appear around a plasma concentration of 160 to 180 mg/dL. The threshold varies with GFR, pregnancy, age, tubular function, medications, and individual transport capacity. Gradual saturation across nephrons creates the splay between first appearance and whole-kidney transport maximum.
Long loops of Henle in juxtamedullary nephrons build the medullary gradient. Water leaves the descending limb, and the water-impermeable thick ascending limb reabsorbs sodium, potassium, and chloride through the sodium-potassium-2 chloride (NKCC2) cotransporter. The early distal tubule reabsorbs sodium and chloride through the sodium-chloride (NCC) cotransporter. Urea recycling and vasa recta countercurrent exchange help preserve the gradient. Vasopressin increases collecting-duct water permeability, allowing water to follow that gradient and concentrate urine. Low vasopressin activity leaves more water in the tubular fluid and produces dilute urine.2
Tubular secretion moves selected substances from peritubular blood into the lumen. Nearly all filtered bicarbonate is normally reclaimed. Net acid excretion occurs chiefly as titratable acid, including hydrogen ions buffered by phosphate, and as ammonium produced by tubular cells. A defect in bicarbonate reclamation or distal acid excretion contributes to renal tubular acidosis. The evaluation combines urine pH with serum electrolytes, bicarbonate, the anion gap, and a validated acidification assessment.
Measuring renal function
GFR estimates assess filtration, which is one part of kidney function. Concentration, acidification, electrolyte handling, endocrine activity, and solute excretion are assessed separately, even when the GFR estimate is normal.3
Filtration markers and eGFR
Estimated GFR (eGFR) uses serum markers and demographic variables in a validated equation.
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| Measurement | What it contributes | Major limitation |
|---|---|---|
| Serum creatinine and creatinine-based eGFR (eGFRcr) | Widely available initial estimate of adult GFR | Creatinine generation varies with muscle mass, diet, exercise, illness, and amputation; tubular secretion and some medications alter the concentration independently of GFR |
| Serum cystatin C and cystatin C-based eGFR (eGFRcys) | Filtration estimate with less dependence on muscle mass | Smoking, obesity, inflammation, glucocorticoids, and thyroid or adrenal disorders can affect cystatin C independently of GFR |
| Combined eGFRcr-cys | Usually improves accuracy when creatinine is unreliable or a decision lies near a threshold | Requires both standardized assays and a validated equation |
| Measured GFR with an exogenous marker | Provides a more accurate value when an important decision requires it | Specialized, time-consuming, and less widely available |
| Measured creatinine clearance | Uses timed urine and paired plasma creatinine to estimate filtration | Incomplete timing and collection are common; tubular secretion usually makes clearance exceed true GFR |
Urea clearance is limited by variable tubular reabsorption. Inulin has historically provided a close measure of GFR, but it requires infusion and timed sampling. Iohexol, iothalamate, and selected radionuclide methods support current measured-GFR procedures. Serum beta-2 microglobulin reflects filtration as well as production and inflammation. Increased urine beta-2 microglobulin supports impaired proximal tubular reabsorption. Creatinine methods also have assay-specific drug and substance interferences.2,3
For adults age 18 years and older, US laboratories commonly use the race-free 2021 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) creatinine equation for the initial estimate. The report identifies the equation and reports eGFR in mL/min/1.73 m2. A combined creatinine-cystatin C equation is useful when creatinine is likely to misrepresent GFR or greater accuracy affects a decision. Children require an equation validated for a comparable pediatric population. During unstable kidney function, every steady-state estimating equation has limited accuracy.3,4
The calculation, timed-collection checks, body-surface-area indexing, and clearance examples are in Timed Urine and Renal Clearance Calculations.
GFR categories in chronic kidney disease
Kidney Disease: Improving Global Outcomes (KDIGO) defines chronic kidney disease (CKD) as an abnormality of kidney structure or function that persists for at least 3 months and has implications for health. Classification combines cause, GFR category, and albuminuria category. G1 and G2 require another marker of kidney damage, such as persistent albuminuria, persistent hematuria, an abnormal urine sediment, tubular electrolyte losses, histologic or imaging abnormalities, or a kidney transplant history.3
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| GFR category | eGFR, mL/min/1.73 m2 | KDIGO description |
|---|---|---|
| G1 | ≥90 | Normal or high |
| G2 | 60 to 89 | Mildly decreased |
| G3a | 45 to 59 | Mildly to moderately decreased |
| G3b | 30 to 44 | Moderately to severely decreased |
| G4 | 15 to 29 | Severely decreased |
| G5 | <15 | Kidney failure |
Concentrating and acidification tests
Urine concentration can become abnormal before a large change appears in GFR. Interpretation starts by comparing urine concentration with hydration, serum sodium, serum osmolality, urine volume, medications, and the clinical setting. The Specific Gravity and Osmolality lesson covers the measurement differences.
A water-deprivation test follows a medically supervised protocol with serial body weight, vital signs, urine volume and osmolality, serum sodium, and serum osmolality. The procedure includes stopping criteria for excessive weight loss, rising sodium, orthostasis, or intolerable symptoms. Desmopressin may follow the deprivation phase. An increase in urine osmolality supports preserved renal response to vasopressin and can support central vasopressin deficiency. A limited response can support renal vasopressin resistance. Partial disorders and primary polydipsia overlap, so the complete protocol and, where available, testing based on copeptin (a stable fragment of the vasopressin precursor) guide classification.5
Osmolar clearance describes the plasma volume cleared of osmoles per minute. Free-water clearance compares that value with urine flow:
Cosm = (Uosm × V) ÷ Posm
CH2O = V − Cosm
For a urine osmolality of 680 mOsm/kg, plasma osmolality of 290 mOsm/kg, and urine flow of 1.0 mL/min:
Cosm = (680 mOsm/kg × 1.0 mL/min) ÷ 290 mOsm/kg = 2.34 mL/min
CH2O = 1.0 mL/min − 2.34 mL/min = −1.34 mL/min
The negative result indicates net water conservation. A positive result indicates excretion of water beyond the osmoles being cleared. These calculations require paired urine and plasma osmolality and a timed urine flow.2
Urinary ammonium and titratable acidity help characterize impaired acid excretion. Proximal renal tubular acidosis chiefly reflects impaired bicarbonate reclamation. Distal renal tubular acidosis reflects impaired distal hydrogen-ion secretion. Type 4 renal tubular acidosis involves impaired aldosterone action with reduced ammonium production and excretion. Provocative tests require a validated supervised procedure. Classification combines urine pH with serum acid-base findings, electrolytes, urinary ammonium assessment, and the response to any validated challenge.2
Clearance of p-aminohippurate approximates effective renal plasma flow because functional proximal tubules extract and secrete most of the infused marker during one renal passage. Extraction is incomplete, and the infusion procedure is now confined mainly to specialized testing and research.2
Urine patterns and anatomic localization
Urinalysis helps locate injury when the laboratory considers specimen quality, chemistry, microscopy, and culture together with kidney function and the clinical context. The Urine Microscopy lesson covers particle morphology and reporting.6,7
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| Predominant site or process | Supporting urine pattern | Important follow-up |
|---|---|---|
| Glomerular inflammation | Hematuria, dysmorphic RBCs or acanthocytes, RBC casts, and variable proteinuria | Quantitative albumin or protein, creatinine/eGFR, complement and disease-directed serology, and kidney biopsy when indicated |
| Glomerular permeability or podocyte injury | Marked albuminuria or proteinuria, lipiduria, oval fat bodies, and fatty casts; sediment may otherwise be bland | Quantitative protein assessment, serum albumin and lipids, kidney function, disease-directed serology, and biopsy when indicated |
| Acute tubular injury | Renal tubular epithelial cells and casts, granular or muddy-brown casts, mild proteinuria, and impaired concentration | Creatinine trend, urine output, hemodynamic and exposure review, and selected pigment or toxicology studies |
| Proximal tubular dysfunction | Normoglycemic glycosuria, aminoaciduria, phosphate and bicarbonate wasting, and low-molecular-weight proteinuria | Paired blood measurements and targeted evaluation for Fanconi syndrome, monoclonal light chains, drugs, toxins, or an inherited disorder |
| Tubulointerstitial inflammation | Pyuria, white blood cell (WBC) casts, mild proteinuria, and microscopic hematuria | Medication and exposure review, culture when infection is possible, kidney function, and biopsy in selected cases |
| Upper urinary tract infection | Pyuria, bacteriuria, leukocyte esterase, and sometimes WBC casts | Properly collected urine culture and clinical assessment; imaging when obstruction or complication is suspected |
| Lower urinary tract inflammation | Pyuria, bacteriuria, hematuria, and mild proteinuria without a renal cast pattern | Culture and clinical correlation |
| Advanced chronic parenchymal injury | Impaired concentration with granular, waxy, or broad casts in some patients | Persistent eGFR and albuminuria assessment, electrolyte studies, imaging, and cause-directed evaluation |
Urine eosinophils are weak and nonspecific in suspected acute interstitial nephritis and provide limited diagnostic support. Diagnosis rests on the complete clinical and laboratory pattern, with kidney biopsy used in selected cases.6
Glomerular disease patterns
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| Pattern or disorder | Urine findings | Laboratory confirmation or classification |
|---|---|---|
| Postinfectious glomerulonephritis | Hematuria, dysmorphic RBCs, RBC casts, proteinuria, and sometimes WBCs | Complement testing and evidence of the preceding infection, such as antistreptolysin O (ASO) or anti-DNase B after streptococcal infection; clinical evaluation and biopsy in atypical cases |
| Rapidly progressive glomerulonephritis | Active nephritic sediment with a rapidly rising creatinine | Urgent anti-glomerular basement membrane (anti-GBM) antibody, proteinase 3 antineutrophil cytoplasmic antibody (PR3-ANCA), myeloperoxidase antineutrophil cytoplasmic antibody (MPO-ANCA), complement, antinuclear antibody (ANA), infection studies, and kidney biopsy selected from the presentation |
| Anti-GBM disease | Hematuria, proteinuria, RBC casts, and rapidly impaired filtration; pulmonary hemorrhage may accompany renal disease | Anti-GBM antibody and kidney biopsy |
| ANCA-associated vasculitis, including granulomatosis with polyangiitis | Hematuria, proteinuria, RBC casts, and impaired filtration | Antigen-specific PR3-ANCA and MPO-ANCA immunoassays interpreted with clinical assessment and biopsy |
| IgA nephropathy | Episodic or persistent hematuria with variable proteinuria | Kidney biopsy showing IgA-dominant or codominant deposits is required for diagnosis |
| IgA vasculitis with kidney involvement | Hematuria, variable proteinuria, and sometimes RBC casts with a compatible systemic presentation | Clinical assessment, skin biopsy in selected cases, and kidney biopsy when renal severity or diagnostic uncertainty requires it |
| Membranous nephropathy | Proteinuria that can reach nephrotic range, with microscopic hematuria in some patients | Phospholipase A2 receptor testing, evaluation for secondary causes, and kidney biopsy as indicated |
| Membranoproliferative glomerular injury pattern | Hematuria, proteinuria, and variable complement reduction | Kidney biopsy with immunofluorescence and electron microscopy, followed by evaluation for immune-complex disease, monoclonal protein, infection, autoimmune disease, or complement dysregulation |
| Immune-complex glomerulonephritis or complement-mediated glomerulonephritis | Hematuria, proteinuria, and variable complement reduction | Kidney biopsy with immunofluorescence and electron microscopy, followed by cause-directed infection, autoimmune, monoclonal-protein, and complement studies |
| Hereditary basement-membrane disease, including Alport syndrome | Persistent microscopic hematuria, sometimes with proteinuria; hearing and ocular findings may provide context | Kidney or skin studies and molecular testing selected for the suspected disorder |
| Diabetic kidney disease | Persistent albuminuria with a falling eGFR; the sediment is often bland | Repeat quantitative urine albumin-creatinine ratio (UACR), eGFR trend, and clinical assessment for concordant diabetes and alternative kidney disease |
Antigen-specific ANCA results are interpreted with the clinical presentation and biopsy. IgA nephropathy requires kidney biopsy because a validated serum or urine diagnostic biomarker is unavailable.8-10
Nephrotic syndrome in adults includes nephrotic-range proteinuria, commonly greater than 3.5 g/24 h, together with hypoalbuminemia and edema. Hyperlipidemia, lipiduria, oval fat bodies, and fatty casts may accompany the pattern. Minimal change disease, focal segmental glomerulosclerosis, membranous nephropathy, diabetes, amyloidosis, and other disorders can produce this presentation. The urine pattern establishes the severity and suggests glomerular permeability injury. Serology and kidney biopsy classify the cause.8-10
A bland sediment with slowly declining kidney function, early hyperuricemia or gout, and an autosomal dominant family pattern can prompt evaluation for autosomal dominant tubulointerstitial kidney disease due to UMOD variants. Molecular testing establishes the genetic cause.11
Acute kidney injury
Acute kidney injury (AKI) is a rapid change in kidney function. Urine output may fall, remain preserved, or change after the serum creatinine response. As of August 29, 2026, the KDIGO 2012 AKI guideline remains the latest final KDIGO guideline. A 2026 AKI and acute kidney disease update is in public review.12
AKI is present when any one of these KDIGO criteria is met:
- serum creatinine rises by at least 0.3 mg/dL within 48 hours;
- serum creatinine rises to at least 1.5 times baseline within the prior 7 days; or
- urine output is below 0.5 mL/kg/h for at least 6 hours.
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| Stage | Serum creatinine or eGFR criterion | Urine output criterion |
|---|---|---|
| 1 | 1.5 to 1.9 times baseline or an increase of at least 0.3 mg/dL | <0.5 mL/kg/h for 6 to 12 hours |
| 2 | 2.0 to 2.9 times baseline | <0.5 mL/kg/h for at least 12 hours |
| 3 | At least 3 times baseline, an increase to at least 4.0 mg/dL, initiation of kidney replacement therapy, or, in patients younger than 18 years, a decrease in eGFR to <35 mL/min/1.73 m2 | <0.3 mL/kg/h for at least 24 hours or anuria for at least 12 hours |
Prerenal hypoperfusion, intrinsic renal injury, and postrenal obstruction form the initial localization. A bland sediment or hyaline casts can accompany hypoperfusion. RBC casts support a glomerular process. Renal tubular epithelial cells and muddy-brown casts support tubular injury. WBC casts support renal inflammation or infection. Suspected obstruction requires clinical and imaging assessment.
Kidney stones
Stones form when urine becomes supersaturated with a poorly soluble substance. Urine volume, pH, calcium, oxalate, uric acid, citrate, infection, medications, and inherited transport disorders can change that saturation. Crystalluria shows that precipitation occurred in the specimen. The clinical presentation and imaging establish a stone. Analysis of a recovered stone identifies its composition. For a recurrent or high-risk stone former, a validated metabolic evaluation may include one or two 24-hour collections for volume, pH, calcium, oxalate, uric acid, citrate, sodium, potassium, and creatinine.13
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| Stone type | Urine setting | Useful laboratory action |
|---|---|---|
| Calcium oxalate or calcium phosphate | Calcium stones are the most common; low urine volume, hypercalciuria, hyperoxaluria, hypocitraturia, and urine pH influence risk | Analyze a recovered stone and perform risk-directed serum and timed urine testing |
| Struvite, magnesium ammonium phosphate | Urease-producing infection with alkaline urine | Culture the urine and analyze the stone |
| Uric acid | Persistently acidic urine and increased uric acid load can favor precipitation | Measure urine pH and uric acid according to the stone evaluation |
| Cystine | Cystinuria with hexagonal crystals or recurrent cystine stones | Quantify urine cystine, analyze the stone, and use SLC3A1/SLC7A9 testing when indicated |
Microscopic hematuria often accompanies stone passage. The urine crystal table compares morphology and confirmation. Crystal identity can indicate which substance is supersaturated and guide follow-up testing.
Inherited and metabolic urine findings
An overflow pattern develops when a metabolite accumulates in plasma and exceeds tubular reabsorptive capacity. A renal pattern develops when tubular transport fails and a normally reclaimed substance remains in urine. Color, odor, a strip reaction, or a crystal can start the investigation. State newborn-screening panels vary. The federal Recommended Uniform Screening Panel provides national recommendations.14 Current confirmation generally uses quantitative amino acid or organic acid analysis, mass spectrometry, enzyme assays, and molecular testing.15
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| Disorder or group | Urine clue | Current laboratory direction |
|---|---|---|
| Phenylalanine hydroxylase deficiency | Phenylketones and a musty odor are late, nonspecific clues | Newborn dried-blood-spot screening, plasma phenylalanine and tyrosine, pterin or dihydropteridine reductase studies when indicated, and molecular confirmation15,16 |
| Maple syrup urine disease | Ketonuria, branched-chain ketoacids, and a maple-like odor may appear during decompensation | Newborn screening followed by quantitative plasma amino acids and alloisoleucine, urine organic acids, and molecular testing15,17 |
| Tyrosinemia and tyrosyluria | Tyrosine metabolites or succinylacetone may appear in urine, depending on the enzyme defect | Quantitative succinylacetone for type I, plasma amino acids, urine organic acids, and molecular testing15 |
| Alkaptonuria | Urine containing homogentisic acid may darken on standing or with alkalinization | Quantitative urine homogentisic acid by gas chromatography with mass spectrometry or liquid chromatography with tandem mass spectrometry, followed by homogentisate 1,2-dioxygenase (HGD) molecular testing18 |
| Organic acidemias and methylmalonic acid disorders | Characteristic organic acids and, during illness, ketones may appear in urine | Blood acylcarnitines, plasma amino acids, quantitative urine organic acids, vitamin and cofactor studies where indicated, and molecular testing15 |
| Hartnup disease and other amino acid transport disorders | A characteristic aminoaciduria pattern; blue discoloration from indican is an uncommon and nonspecific clue | Quantitative urine amino acid analysis and molecular testing2 |
| Cystinuria | Hexagonal crystals, increased urine cystine, and cystine stones | Quantitative urine cystine, stone analysis, and SLC3A1/SLC7A9 testing19 |
| Cystinosis | Fanconi pattern with normoglycemic glycosuria, aminoaciduria, phosphate and bicarbonate wasting, and low-molecular-weight proteinuria | Leukocyte cystine measurement and CTNS testing20 |
| Homocystinuria | Historical sulfhydryl screens may react | Plasma total homocysteine and methionine, enzyme studies, and molecular testing21 |
| Acute hepatic porphyria | Urine may become red-brown; symptoms can occur before visible color change | Random urine porphobilinogen, aminolevulinic acid, and creatinine during symptoms, followed by porphyria-specific biochemical and molecular testing22 |
| Mucopolysaccharidosis | Increased urinary glycosaminoglycans | Quantitative urine glycosaminoglycans with pattern analysis, followed by enzyme and molecular confirmation23 |
| Hypoxanthine phosphoribosyltransferase 1 (HPRT1) deficiency, including Lesch-Nyhan disease | Orange uric acid crystals can appear in an infant's diaper | Serum and urine uric acid assessment, enzyme studies, and HPRT1 testing24 |
| Galactosemia and other meliturias | A copper-reduction reaction with a negative glucose oxidase result suggests a reducing substance other than glucose | Newborn screening and targeted carbohydrate, enzyme, and molecular testing25 |
Phenylalanine hydroxylase deficiency, maple syrup urine disease, homocystinuria, and tyrosinemia type I are among the core conditions on the federal screening panel.14 For maple syrup urine disease, plasma alloisoleucine above 5 µmol/L strongly supports the diagnosis in the appropriate assay and clinical setting.17 In alkaptonuria, darkening of the specimen prompts testing. Quantitative urinary homogentisic acid establishes the biochemical diagnosis.18
Urine 5-hydroxyindoleacetic acid testing depends on a defined specimen and method. Reference intervals, preservatives, diet and medication restrictions, and collection duration follow the performing laboratory's current instructions.26 The reagent-strip lesson covers the urine patterns for monoclonal light chains, myoglobin, glucose, ketones, bilirubin, and heme.
Historical qualitative screening reactions
The reactions below remain useful for examination review and for recognizing older laboratory records. They provide preliminary chemical clues. Current diagnosis uses the specific methods in the preceding table.2,15,22
Older descriptions include hazardous reagents and exact operating steps. This table preserves the recognition target and classic endpoint while omitting preparation amounts and performance steps. Patient testing requires the laboratory's validated standard operating procedure.
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| Historical reaction | Classic positive reaction | Main limitation and current direction |
|---|---|---|
| Ferric chloride | Blue-green with phenylpyruvate, transient deep blue with homogentisic acid, or gray-black with older melanogen methods | Nonspecific color reaction; confirm the suspected analyte with a quantitative biochemical method |
| Nitroso-naphthol | Orange-red reaction with tyrosine metabolites | Historical screen; use quantitative amino acid, succinylacetone, organic acid, and molecular studies |
| Silver nitrate | Black reaction with homogentisic acid | Historical alkaptonuria screen; use quantitative homogentisic acid measurement |
| 2,4-dinitrophenylhydrazine | Yellow turbidity or precipitate from ketoacid hydrazones | Several ketoacids react; evaluate suspected maple syrup urine disease with plasma amino acids, alloisoleucine, and urine organic acids |
| Cyanide-nitroprusside | Red-purple reaction with cystine or homocysteine | Hazardous and nonspecific; use quantitative cystine or plasma homocysteine testing with disease-directed confirmation |
| Silver-nitroprusside | Red-purple reaction with homocysteine in the historical method | Hazardous historical screen; use plasma total homocysteine, methionine, enzyme studies, and molecular testing |
| Hoesch or Watson-Schwartz | Red Ehrlich reaction and historical solvent-separation pattern for porphobilinogen | Use quantitative urine porphobilinogen, aminolevulinic acid, and creatinine during symptoms |
| Cetyltrimethylammonium bromide (CTAB) turbidity | Turbidity from urinary glycosaminoglycans | Use quantitative glycosaminoglycan measurement with pattern, enzyme, and molecular confirmation |
| Copper reduction | Color sequence caused by glucose or another reducing substance | Several reducing substances react; identify the analyte with a specific enzymatic, chromatographic, or mass-spectrometric method |
| Ammonium sulfate precipitation | Historical separation of hemoglobin from myoglobin in heme-positive urine | Use plasma appearance, creatine kinase, hemolysis studies, microscopy, and validated pigment methods |
For nonwaived testing, a laboratory that modifies a Food and Drug Administration (FDA)-cleared or approved test or uses a method without manufacturer performance specifications must establish the applicable performance specifications before reporting patient results.27
Practice
References
- National Institute of Diabetes and Digestive and Kidney Diseases. Your Kidneys & How They Work. Accessed August 29, 2026. Back to text
- Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids. 7th ed. F.A. Davis; 2021. ISBN 978-0-8036-7582-7. F.A. Davis catalog record. Back to text
- Kidney Disease: Improving Global Outcomes 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 Back to text
- National Kidney Foundation. Recommendations for Implementing the CKD-EPI 2021 Race-Free eGFR Calculation: Guidelines for Clinical Laboratories. Accessed August 29, 2026. Back to text
- National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes Insipidus. Accessed August 29, 2026. Back to text
- Cavanaugh C, Perazella MA. Urine sediment examination in the diagnosis and management of kidney disease: Core Curriculum 2019. Am J Kidney Dis. 2019;73(2):258-272. doi:10.1053/j.ajkd.2018.07.012 Back to text
- Kouri TT, Hofmann W, Falbo R, et al. The EFLM European urinalysis guideline 2023. Clin Chem Lab Med. 2024;62(9):1653-1786. doi:10.1515/cclm-2024-0070 Back to text
- Kidney Disease: Improving Global Outcomes. KDIGO 2021 Glomerular Diseases Guideline. Accessed August 29, 2026. Back to text
- Kidney Disease: Improving Global Outcomes. KDIGO 2024 ANCA-Associated Vasculitis Guideline. Accessed August 29, 2026. Back to text
- Kidney Disease: Improving Global Outcomes. KDIGO 2025 IgA Nephropathy and IgA Vasculitis Guideline. Accessed August 29, 2026. Back to text
- Bleyer AJ, Kidd K, Zivná M, Kmoch S. Autosomal dominant tubulointerstitial kidney disease due to UMOD variants. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Autosomal Dominant Tubulointerstitial Kidney Disease - UMOD. Accessed August 29, 2026. Back to text
- Kidney Disease: Improving Global Outcomes Acute Kidney Injury Work Group. KDIGO clinical practice guideline for acute kidney injury. Kidney Int Suppl. 2012;2(1):1-138. doi:10.1038/kisup.2012.1 KDIGO guideline and 2026 public-review update page. Back to text
- Pearle MS, Goldfarb DS, Assimos DG, et al. Medical management of kidney stones: AUA guideline. J Urol. 2014;192(2):316-324. doi:10.1016/j.juro.2014.05.006 Back to text
- Health Resources and Services Administration, Maternal and Child Health Bureau. Newborn Screening Programs and the Recommended Uniform Screening Panel. Accessed August 29, 2026. Back to text
- American College of Medical Genetics and Genomics. Newborn Screening ACT Sheets and Algorithms. Accessed August 29, 2026. Back to text
- Arnold G, Vockley J. Phenylalanine hydroxylase deficiency. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Updated November 20, 2025. Phenylalanine Hydroxylase Deficiency. Accessed August 29, 2026. Back to text
- Strauss KA, Puffenberger EG, Carson VJ. Maple syrup urine disease. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Updated April 23, 2020. Maple Syrup Urine Disease. Accessed August 29, 2026. Back to text
- Introne WJ, Perry M, Chen M. Alkaptonuria. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Updated June 10, 2021. Alkaptonuria. Accessed August 29, 2026. Back to text
- Spasiano A, Halbritter J, Ferraro PM. Cystinuria. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Published November 20, 2025. Cystinuria. Accessed August 29, 2026. Back to text
- Nesterova G, Gahl WA. Cystinosis. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Updated August 14, 2025. Cystinosis. Accessed August 29, 2026. Back to text
- Sacharow SJ, Levy HL. Homocystinuria due to cystathionine beta-synthase deficiency. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Updated September 25, 2025. Homocystinuria Due to Cystathionine Beta-Synthase Deficiency. Accessed August 29, 2026. Back to text
- Wang B, Bonkovsky HL, Lim JK, Balwani M. AGA clinical practice update on diagnosis and management of acute hepatic porphyrias: expert review. Gastroenterology. 2023;164(3):484-491. doi:10.1053/j.gastro.2022.11.034 Back to text
- Clarke LA. Mucopolysaccharidosis type I. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Revised December 4, 2025. Mucopolysaccharidosis Type I. Accessed August 29, 2026. Back to text
- Jinnah HA. HPRT1 disorders. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Updated August 6, 2020. HPRT1 Disorders. Accessed August 29, 2026. Back to text
- Berry GT. Classic galactosemia and clinical variant galactosemia. In: Adam MP, Bick S, Mirzaa GM, et al, eds. GeneReviews. University of Washington, Seattle; 1993-2026. Classic Galactosemia and Clinical Variant Galactosemia. Accessed August 29, 2026. Back to text
- Mayo Clinic Laboratories. 5-Hydroxyindoleacetic Acid, 24 Hour, Urine. Accessed August 29, 2026. Back to text
- 42 CFR §493.1253. Establishment and verification of performance specifications. Electronic Code of Federal Regulations. Accessed August 29, 2026. Back to text