Urinalysis: dipstick, microscopy, ACR and PCR

Urinalysis is the examination of urine by eye, by dipstick chemistry and, when needed, by microscopy. It is one of the commonest tests in medicine because a small sample of urine carries information about infection, kidney damage, stones, metabolic disease and liver disease. No single dipstick line makes a diagnosis; the test is read as a pattern, against the way the sample was collected and against the patient in front of you.

This page covers how urine is collected, what dipstick and microscopy measure and their known false positives and negatives, dysmorphic red cells as a pointer to glomerular disease, the albumin to creatinine ratio (ACR) and the protein to creatinine ratio (PCR) with the KDIGO bands, haematuria pathways and the diagnosis of urinary tract infection (UTI). Ranges vary by laboratory, age, sex and method, so the laboratory's own printed reference range always wins.

Five kinds of information come from a urinalysis.^[1]

• Collection. Whether the sample is mid-stream, timed or first morning urine changes what protein and cell counts mean.
• Dipstick chemistry. Reagent pads estimate pH, specific gravity and the presence of protein, blood, glucose, ketones, bilirubin, urobilinogen, leukocyte esterase and nitrite.
• Microscopy. Centrifuged sediment (or automated digital imaging) shows cells, casts, crystals, bacteria and yeast.
• ACR. The ratio of urine albumin (mg) to creatinine (g or mmol) in a spot sample, which replaces many 24-hour collections for albuminuria.
• PCR. The ratio of total urine protein to creatinine, useful when non-albumin proteins dominate.

Abbreviations used throughout: ACR, albumin to creatinine ratio; PCR, protein to creatinine ratio; HPF, high power field; RBC, red blood cell; WBC, white blood cell; UTI, urinary tract infection; KDIGO, Kidney Disease: Improving Global Outcomes; EAU, European Association of Urology.

Collection is the step that ruins the most results. Get it wrong and the rest of the report is misleading.

• Mid-stream (clean catch) urine. The patient cleans the urethral opening, passes the first part of the stream into the toilet, then collects the mid portion without stopping. This reduces squamous epithelial cells and surface flora. It is the routine sample for dipstick and culture.^[3]
• First morning urine. The most concentrated sample; best for protein (especially when orthostatic proteinuria is to be excluded) and for cell counts. A first morning sample is required in some centres for an accurate ACR and for microscopy if the void is dilute.
• Timed (24-hour) collection. Used for total protein quantification when a spot ratio is unreliable, and historically for creatinine clearance. Patients spill part of it often, so a spot ACR or PCR is preferred today.
• Suprapubic aspirate or catheter urine in children, or when contamination is suspected. Always record the method on the request.

For ACR and PCR, the sample should not be taken after exercise, during fever or menstruation, and not from a specimen left at room temperature for hours.

The reagent strip is a semi-quantitative screening test, not a precise measurement.

• Protein. Sensitive to albumin but not to tubular proteins or immunoglobulin light chains. The colour block is semi-quantitative, so the manufacturer's read chart for the exact strip must be used. False negatives with dilute urine, non-albumin proteins and Bence Jones proteins.^[2]
• Blood. Detects haemoglobin (including myoglobin). False positives from menstrual blood, oxidising cleaners and peroxidases; false negatives from high ascorbic acid and from vitamin C.^[2]
• Leukocyte esterase (LE). Detects an enzyme from intact neutrophils. False positives from oxidising agents and coloured urine; false negatives with high glucose, high specific gravity, formaldehyde preservative and with non-neutrophil inflammation.^[2]
• Nitrite. Formed when bacteria convert urinary nitrate. A negative nitrite never excludes infection: short bladder incubation, infection with non-nitrate-reducing organisms or low nitrate intake (most Enterococcus and Staphylococcus) all give false negatives.^[2][3]
• Glucose. Detects reducing substances via a glucose oxidase pad. Renal glycosuria or pregnancy can make it positive without diabetes; ascorbic acid and ketones in excess can interfere.^[2]
• Ketones (acetoacetate). Positive in fasting, vomiting, low carbohydrate intake and diabetic ketoacidosis. False positives in highly pigmented urine; false negatives when beta-hydroxybutyrate predominates (it is not detected).^[2]
• Bilirubin. Conjugated (direct) bilirubin is water soluble and filtered. Visible blood and ascorbic acid can cause false negatives; some metabolites cause false positives. A positive pad points to hepatobiliary disease or conjugated hyperbilirubinaemia.^[2]
• Urobilinogen. Rises in haemolysis and hepatocellular dysfunction; falls in complete biliary obstruction. Ascorbic acid and some drugs (sulphonamides, phenazopyridine, p-aminobenzoic acid) interfere.^[2]
• pH. Typical fresh urine is acidic to slightly alkaline. Diet (vegetarian, citrate), infection with urease-producing organisms (very alkaline) and stones change it.
• Specific gravity. A rough guide to concentrating ability. False highs with protein or ketoacids; falsely affected by glucose and alkaline samples.^[2]

Microscopy separates glomerular from urological disease and identifies substrate:

• RBCs. None to a few per HPF is expected; the exact upper limit is the one printed by the laboratory. Dysmorphic RBCs, especially acanthocytes (G1 cells), imply glomerular bleeding.
• WBCs (pyuria). Few cells per HPF are expected; contamination from genital secretions is common in women.
• Casts. Hyaline casts can be physiological after exercise. Cellular casts point to renal parenchymal disease: RBC casts (glomerulonephritis, vasculitis), WBC casts (pyelonephritis, interstitial nephritis), epithelial cell casts (tubular injury). Waxy and broad casts appear in chronic kidney disease.
• Crystals. Calcium oxalate (envelope or dumb-bell), uric acid, triple phosphate (coffin lid) and cystine hexagons. Fresh urine crystalluria can be benign; persistently abnormal crystals, or crystals with renal colic, point to stone composition.
• Bacteria and yeast. Seen with infection or contamination; confirm with culture.

ACR is the recommended first screen for albuminuria and CKD risk in adults. The KDIGO albuminuria categories are:^[4]

Persistent albuminuria is CKD even if the estimated GFR is normal. Microalbuminuria is the older term for the A2 band; many laboratories now report ACR directly.

PCR (total protein to creatinine ratio) measures all urinary protein, not just albumin. It is used when tubular or overflow proteinuria is suspected (myeloma light chains, tubulointerstitial disease) and when a nephrotic-range result is needed. A PCR of at least 3.5 g/g is the conventional threshold for nephrotic-range proteinuria.^[5] Proteinuria is quantified on a spot PCR much as ACR is.

The PCR bands are only approximate: ACR and PCR do not move in parallel when the protein is not albumin, so use the panel's preferred test for the question.

Dipstick blood is confirmed by microscopy; confirmed haematuria means red cells above the laboratory's microscopy threshold on more than one occasion, or a clearly positive dipstick with no infection. Repeat a negative first sample: transient haematuria (exercise, fever, menstruation) is common.

• Glomerular (nephritic) pathway. Dysmorphic RBCs and/or acanthocytes, red cell casts, proteinuria and often hypertension and oedema. The European consensus recommends at least 40 percent dysmorphic RBCs or at least 2 percent acanthocytes, or RBC casts, as suggestive of glomerular bleeding; higher percentages (at least 80 percent dysmorphic or at least 5 percent acanthocytes) are more strongly suggestive. A count under 20 erythrocytes per microlitre makes dysmorphic assessment unreliable.^[6]
• Non-glomerular (urological) pathway. Uniform (isomorphic) RBCs, tissue disease, stones, tumours and infection. Clots point to a urological source.
• Mixed or medical work-up. Reassess RBC casts are not present, ACR is measured, bloods (creatinine, complement, serology as indicated) and imaging follow the local haematuria pathway.

Persistent microscopic haematuria in adults needs a full evaluation: glomerular disease, stone, tumour, infection, benign prostatic hyperplasia and medication-related causes.

These are the two classical glomerular pictures; most real disease is somewhere between them.^[6]

• Nephritic (glomerulonephritis). Inflammation of the glomerulus: haematuria (often visible, "cola-coloured"), RBC casts in the urine, mild to moderate proteinuria, hypertension, oliguria and oedema. Complement may be low; creatinine rises.
• Nephrotic syndrome. Heavy albumin loss: massive proteinuria (at least 3.5 g/24 h, or PCR at least 3.5 g/g), hypoalbuminaemia, oedema and hyperlipidaemia. Haematuria may be absent; casts are lipid-laden oval fat bodies, and fatty casts are characteristic.
• Overlap. IgA nephropathy and lupus nephritis often have both nephritic urinary abnormalities and nephrotic-range proteinuria.

The diagnosis is clinical; urine testing supports it. In women, age and the setting change the rules.

• NICE and UKHSA guidance: empirical treatment is considered in women under 65 when two or more of dysuria, frequency, urgency, visible haematuria or nocturia are present; laboratory tests are used selectively.^[7]
• EAU (current guideline): urinalysis, including assessment of white and red blood cells and nitrite, is recommended as a routine test; urine culture and susceptibility testing should be performed in all cases of pyelonephritis. Take a midstream dipstick for nitrite and leukocytes when acute bacterial prostatitis is suspected. Urine dipstick testing for nitrite and leukocytes has a positive predictive value of 95 percent and a negative predictive value of 70 percent in acute bacterial prostatitis.^[3]
• Diagnostic inference. In symptomatic women, nitrite and LE together improve the likelihood of infection, but a negative dipstick in a high-probability patient is not decisive; culture is used when it would change management.
• Asymptomatic bacteriuria (positive culture without symptoms) is common and is not treated in most non-pregnant adults; it is treated in pregnancy.
• Catheter-associated UTI has its own higher quantitative thresholds (at least 10^3 colony-forming units per millilitre in catheter or recently removed catheter urine) and is not a reason to treat asymptomatic colonisation.^[3]

Normal urine is dilute to concentrated, slightly acidic to alkaline, and contains little or no protein, glucose, ketones, bilirubin or blood. Ranges differ by laboratory, age, sex and method, so the laboratory's own printed range always wins. MedlinePlus states that normal value ranges vary slightly among different labs and that some labs use different measurements or different samples.^[1]

Named combinations that point to a cause. They are starting points, not diagnoses.

• Nephritic pattern. Visible or microscopic haematuria with dysmorphic RBCs or RBC casts, proteinuria, hypertension and often oliguria. Think glomerulonephritis, vasculitis or IgA nephropathy.^[6]
• Nephrotic pattern. Heavy proteinuria (at least 3.5 g/24 h or PCR at least 3.5 g/g), hypoalbuminaemia, oedema and hyperlipidaemia, often with lipiduria. Think minimal change disease, membranous nephropathy, FSGS, amyloid or diabetic kidney disease.^[5]
• Active urinary sediment. Pyuria plus white cell casts suggests pyelonephritis or interstitial nephritis; eosinophils in the urine (special stain) point to acute interstitial nephritis.
• UTI pattern. Dysuria, frequency, urgency, positive nitrite and/or leukocyte esterase, WBCs and (sometimes) RBCs. A positive nitrite is strongly suggestive of infection in symptomatic patients; a negative dipstick does not exclude it.^[3][7]
• Stone pattern. Bloody or crystal-rich urine, pain, often a normal ACR. Crystal type (calcium oxalate, uric acid, struvite) hints at stone composition and pH.
• Tubular pattern. Low molecular weight (tubular) proteinuria with few or no RBCs; ACR may be only modestly raised while PCR is high.
• Overflow pattern. Immunoglobulin light chains and other filtered proteins (myeloma, rhabdomyolysis) may be missed by the protein pad; use PCR and specific assays.
• Contamination pattern. Squamous epithelial cells, mixed flora and a dirty-looking sample; interpret with caution and repeat.
• Concentrated or dehydrated. High specific gravity with ketones; re-check after fluids.
• Dilute. Low specific gravity and false negatives for blood and protein; repeat on a first morning sample.

All three sheets use invented illustrative results, never real patient data. Each is followed by a numbered interpretation and a one-sentence conclusion with the next step.

1. The dipstick is negative for protein, glucose, ketones, blood, bilirubin, LE and nitrite, and the specific gravity and pH sit in the laboratory range.^[1]
2. Microscopy shows no cells, casts or crystals.
3. The ACR is in the A1 band.^[4]
4. Clinical conclusion and next step: this is a normal urinalysis, so no renal investigation is needed; correlate with the clinical reason for testing and repeat only if symptoms or risk factors change.

1. The patient is a woman with dysuria, urgency and frequency.
2. The dipstick shows leukocyte esterase 2+ and nitrite positive, with a trace of blood; the microscopy confirms pyuria and bacteriuria.^[2]
3. In women under 65 with two or more typical symptoms, NICE and UKHSA guidance considers empirical treatment for a suspected UTI without waiting for culture.^[7]
4. The EAU recommends urinalysis for any suspected urinary infection and culture in every case of pyelonephritis; with fever, loin pain or systemic upset, send a midstream urine for culture.^[3]
5. Clinical conclusion and next step: this is uncomplicated lower UTI; treat empirically according to local first-line guidance and reserve a culture for pregnant, male, recurrent or systemic cases.

1. The appearance is smoky brown and microscopy shows 40 to 60 dysmorphic RBCs per HPF, at least 40 percent, plus red cell casts: the European consensus regards this as suggestive of glomerular (nephritic) haematuria.^[6]
2. Proteinuria is moderate, with an ACR of 280 mg/g in the A2 band and a PCR of 1.2 g/g; this is not yet nephrotic range (at least 3.5 g/g).^[4][5]
3. There is no pyuria, bacteria or nitrite, so infection is unlikely; microscopic haematuria above the laboratory threshold with dysmorphic cells indicates a nephritic process.
4. Clinical conclusion and next step: this pattern is a nephritic (glomerulonephritis) pattern; refer for nephrology assessment, bloods (creatinine, complement, ANCA, anti-GBM, serology) and a renal imaging and, where indicated, renal biopsy.

• Do not read one pad in isolation. Infection can be present with a negative nitrite; albuminuria can be present with a negative (or only trace) protein pad if the urine is dilute.
• Contamination masquerades as disease. Squamous cells, mixed bacteria and a dirty sample are signs of a poor collection; repeat before acting.
• Dilute or concentrated urine. Low specific gravity means false negatives for blood and protein; high specific gravity and low pH can false-positive ketones and protein (alkaline pH and protein interference).^[2]
• Myoglobin and haemoglobin. A positive blood pad with few RBCs on microscopy is the signature of rhabdomyolysis or haemolysis; the microscopy saves unnecessary urology.
• Non-albumin proteins. Myeloma light chains and other overflow proteins are missed by the albumin-sensitive protein pad; use PCR (and, where indicated, a urine protein electrophoresis).
• Dysmorphic counts need enough cells. With fewer than 20 erythrocytes per microlitre the assessment is not reliable; report it as a method limitation, not as a negative.^[6]
• ACR and PCR do not move in parallel when the protein is not albumin.
• Urine left standing alters pH, nitrite and any cellular content; process within 1 hour of voiding at room temperature (or within 4 hours if refrigerated).^[2]
• ** menstrual contamination** causes false-positive blood and LE; collect mid-stream or postpone the test.
• Drugs and foods. Phenazopyridine, riboflavin, beets and medications colour the urine and can fool pads and observers.
• Nephrotic-range proteinuria is a threshold, not a disease. It still needs a renal biopsy or nephrology referral to get a diagnosis.