12.4 Urinalysis Interpretation & Urine Specimen Collection
Key Takeaways
- RCSI's renal reading group names urinalysis and urine dipstick interpretation, catheter specimens, clean-catch specimens, CAUTI prevention, dysuria, haematuria, pyuria, Klebsiella pneumoniae and urine output, and urinalysis is one of its photographed OSCE equipment categories.
- A dipstick reading is only valid if the strip is in date, correctly stored, fully immersed, excess urine removed, and read at the exact times printed on the container.
- Leucocyte esterase suggests white cells and nitrites suggest nitrate-reducing bacteria, so both positive strongly supports urinary tract infection, but nitrite-negative does not exclude it because not all uropathogens reduce nitrate.
- Asymptomatic bacteriuria is common in older adults and in catheterised patients and should not be treated with antibiotics; a positive dipstick alone is not a diagnosis of infection.
- A catheter specimen is taken aseptically from the dedicated sampling port, never from the drainage bag and never by disconnecting the closed system.
Urinalysis Interpretation & Urine Specimen Collection
RCSI's Renal reading group is unusually detailed: urinalysis and how to interpret a urine dipstick, UTI, dysuria, haematuria, pyuria, Klebsiella pneumoniae infection, urine output, obtaining a catheter specimen of urine, collecting a clean-catch specimen, strategies to reduce CAUTI, and living with a urinary catheter. Urinalysis is also one of the equipment categories RCSI photographs for the OSCEs - so expect to handle a strip, a container and a chart.
Before the Strip: Look at the Urine
Inspection costs nothing and is often diagnostic.
| Observation | Possible significance |
|---|---|
| Pale, almost colourless | Dilute urine, high fluid intake, diabetes insipidus, diuretics |
| Dark yellow or amber | Concentrated - dehydration |
| Cloudy | Pyuria, bacteriuria, phosphates, mucus. Cloudiness alone is not infection |
| Red or pink | Frank haematuria; also beetroot, rifampicin, some laxatives |
| Brown, "cola" or "tea" coloured | Myoglobinuria in rhabdomyolysis, bilirubin, old blood |
| Green or blue | Certain drugs, dyes, pseudomonas |
| Offensive smell | Infection; note that a strong smell alone in an older adult is not grounds to diagnose UTI |
| Frothy | Significant proteinuria |
Dipstick Technique
Technique determines validity, and it is the part most easily marked at a station.
- Check the expiry date and that the container has been stored correctly with the lid tightly closed - strips deteriorate on exposure to air and moisture.
- Perform hand hygiene and wear gloves and an apron; standard precautions apply to all body fluids.
- Use a fresh specimen, ideally tested within a short time of voiding. Urine left standing becomes alkaline, red cells lyse and bacteria multiply, all of which corrupt the result. Refrigerate if there will be any delay.
- Immerse all reagent pads briefly and completely in the urine.
- Draw the edge of the strip along the rim of the container to remove excess urine, and hold it horizontally - if the strip is held vertically, reagents run from one pad onto the next and produce false results.
- Read each pad at the exact time stated on the container against the colour chart on the container, in good light. Reading too early or too late is the commonest source of error.
- Dispose of the strip and urine appropriately, remove PPE, perform hand hygiene.
- Document every pad result, the appearance of the urine, the time, and the action taken.
Interpreting Each Pad
| Pad | Normal | What an abnormal result suggests |
|---|---|---|
| Leucocyte esterase | Negative | White cells in the urine (pyuria) - infection, inflammation, stones, catheter irritation. Present in asymptomatic bacteriuria too |
| Nitrites | Negative | Nitrate-reducing bacteria, typically Gram-negative organisms such as E. coli, Klebsiella and Proteus. Requires urine to have dwelt in the bladder for some hours, so an early-morning sample is more sensitive |
| Blood | Negative | Haematuria - infection, stones, trauma, catheterisation, tumour, glomerular disease, menstruation. Also positive with myoglobin in rhabdomyolysis |
| Protein | Negative or trace | Kidney disease, infection, heart failure, pre-eclampsia in pregnancy, fever, strenuous exercise |
| Glucose | Negative | Hyperglycaemia exceeding the renal threshold, or a low renal threshold. A positive result warrants a capillary blood glucose |
| Ketones | Negative | Starvation or fasting, vomiting, very low carbohydrate intake, alcohol, and critically diabetic ketoacidosis - ketones with hyperglycaemia is an emergency |
| pH | About 5 to 7 | Alkaline urine occurs with infection by urease-producing organisms such as Proteus, with renal tubular acidosis, or in a stale specimen |
| Specific gravity | About 1.005 to 1.030 | High indicates concentrated urine and dehydration; persistently low and fixed suggests impaired concentrating ability |
| Bilirubin | Negative | Hepatobiliary disease or biliary obstruction |
| Urobilinogen | Small amount normal | Raised in haemolysis and liver disease; absent in complete biliary obstruction |
Nitrites and Leucocytes Together
- Both positive - strongly supportive of urinary tract infection in a symptomatic patient.
- Nitrite positive, leucocytes negative - still suggestive of infection; nitrites are fairly specific.
- Leucocytes positive, nitrite negative - possible infection, but also inflammation, stones, or an organism that does not reduce nitrate. A negative nitrite does not exclude UTI: Enterococcus, Staphylococcus saprophyticus and Pseudomonas do not reliably reduce nitrate, and dilute urine or frequent voiding reduces sensitivity.
- Both negative in a patient with typical symptoms - UTI is less likely, but the clinical picture still governs.
The Asymptomatic Bacteriuria Trap
A positive dipstick is not a diagnosis of infection. Urinary tract infection is a clinical diagnosis supported by urinalysis and culture, not a laboratory finding in isolation.
Asymptomatic bacteriuria - bacteria in the urine without urinary symptoms - is common, and its prevalence rises steeply with age, institutional care and catheterisation. In a long-term catheterised patient, bacteriuria is effectively universal.
Asymptomatic bacteriuria should not be treated with antibiotics in most adults, because treatment does not improve outcomes and does drive resistance, Clostridioides difficile infection and adverse drug effects. The main recognised exception is pregnancy, and treatment may also be indicated before certain urological procedures.
This matters enormously in older-person care. A confused older patient with a positive dipstick is frequently labelled with a UTI while the real cause of the delirium - dehydration, constipation, a new drug, hypoxia, pain, retention - goes unfound. Screen the confusion with the 4AT and work through PINCH ME; do not let a dipstick close the search prematurely.
When to Suspect a Genuine UTI
Localising urinary symptoms: dysuria (pain or burning on passing urine), frequency, urgency, suprapubic pain or tenderness, and new or worsened incontinence. Upper tract involvement is suggested by loin or flank pain, renal angle tenderness, fever and rigors - pyelonephritis is a systemic illness and needs prompt escalation. In frail older adults the presentation may be non-specific, which is exactly why other causes must be excluded rather than assumed away.
Catheter-associated UTI requires signs of systemic infection with no other identified source, not simply cloudy or smelly urine in the bag.
Collecting Specimens Correctly
Midstream Specimen of Urine (MSU) / Clean Catch
The purpose is to reduce contamination by periurethral and perineal flora.
- Explain the procedure and the reason for it, and ensure privacy.
- Ask the person to wash their hands.
- Genital cleansing per local policy - front to back for women; retracting the foreskin where applicable for men.
- Ask the person to begin voiding into the toilet, then place the sterile container into the stream to collect the middle portion, then finish voiding into the toilet.
- Avoid touching the inside of the container or the lid.
- Secure the lid, label the container at the bedside with the patient's details, and complete the request form with the clinical details and any current antimicrobials.
- Send to the laboratory promptly, or refrigerate if there will be delay; a boric acid container may be used where local policy directs.
- Document collection, appearance and dipstick result.
Where a person cannot cooperate, alternatives include a clean-catch collection into a sterile bowl or pad-based collection per local policy. A specimen poured from a bedpan or a urinal is contaminated and is not a valid sample.
Catheter Specimen of Urine (CSU)
The rules here are absolute, and they are examinable.
- Perform hand hygiene; apply gloves and apron; use aseptic technique.
- If the tubing is empty, clamp the tubing below the sampling port for a short period to allow fresh urine to collect - never longer than necessary.
- Clean the dedicated needle-free sampling port with an alcohol wipe and allow it to dry fully.
- Attach a sterile syringe to the port and aspirate the required volume.
- Transfer into a sterile container without touching the rim.
- Unclamp the tubing, ensure free drainage, clean the port again, remove PPE and perform hand hygiene.
- Label at the bedside, complete the request form, send promptly, and document.
Never take a catheter specimen from the drainage bag - the urine there is stale and colonised and the result is meaningless. Never disconnect the catheter from the drainage tubing to obtain a sample: breaking the closed system is one of the principal routes to catheter-associated infection.
Urine Output
- The accepted minimum adult urine output is 0.5 mL/kg/hour. For a 70 kg adult that is 35 mL/hour, and for a 60 kg adult 30 mL/hour. Calculate it rather than eyeballing it.
- Oliguria - output below that threshold - is an early marker of hypoperfusion and acute kidney injury and should prompt assessment and escalation, not simply a note on the chart.
- Anuria demands immediate assessment for obstruction, including a blocked catheter. Check patency before concluding the kidneys have failed.
- Retention presents with suprapubic discomfort and distension, restlessness, and in older patients with new confusion or overflow incontinence. A bladder scan is non-invasive and should precede catheterisation.
- Record intake and output accurately on the fluid balance chart and total it. RCSI lists the fluid balance chart among the documents candidates must be able to complete and interpret - and an untotalled chart is a chart nobody has read.
A urine dipstick in an 85-year-old nursing home resident is positive for leucocytes and nitrites. She has no urinary symptoms but has been more confused since yesterday. What is the correct interpretation?
A nurse needs a urine specimen from a patient with an indwelling urinary catheter. Which method is correct?
A patient has a urine dipstick that is strongly positive for leucocytes but negative for nitrites, with typical dysuria and frequency. How should this be interpreted?