Urine dipstick testing (urinalysis) is a quick, cheap method of urine testing. It is used frequently in primary and secondary care. Beware of false negatives.

Advantages over Urine MC+S

Urine Microscopy, Culture and Sensitivities (MC+S) is the ideal urine test. But it requires sending a sample to the lab, and culture results can take several days. Urine dipstick on the other hand is:

  • Simple
  • Quick
  • Cheap

Disadvantages

  • Not precise

You should only perform a urine dipstick after a full history and thorough examination!

 

Indications

Procedure

Urine dipstick samples are usually self collected by patients. Ideally it should be a mid-stream urine sample (MSU) – this reduces the risk of contamination from the normal bacterial skin flora. You should explain to your patient how to collect the sample:

Men – retract the foreskin, clean the glans penis with a swab. Start to pass urine, and pass the first part into the toilet, then, without stopping the flow, catch some of the middle of the sample in a the sample pot. The pot does not need to be full. Usually 20-30mls is more than enough.
Women – hold back the labia, and clean the vulva with a sterile swab. Start to pass urine, and pass the first part into the toilet, then, without stopping the flow, catch some of the middle of the sample in a sample pot. The pot does not need to be full. Usually 20-30mls is more than enough.
  • Don’t open the bottle until you are ready to take the sample – it should be sterile inside the container – taking the lid off and leaving it open to the air can increase the risk of ocntamination
  • The amount of urine is not that important. Tell patients they don’t have to completely fill the bottle!
  • The sample should be tested within 2 hours. If this is not possible, you may be able to preserve the sample to some extent by keeping in the fridge

Testing a Urine Sample – The Procedure

  1. Wash hands, put on gloves
  2. Look at the sample pot – check it is the right patient and the right date. You also want to know if it was taken in the last 2 hours – a crude way to know if it is recent is to see if it is warm!
  3. Look in the bottle – are there any precipitations?
    1. Does it look a normal colour?
    2. Normal – straw yellow
    3. Dark – bile pigments may be present due to dehydration
    4. Red – haematuria, menstrual blood?, food; e.g. beetroot and blackberries
    5. Green/blue – Pseudomonal UTI, triamterene (this is a potassium sparing diuretic), asparagus
    6. Orange – dehydration (bile pigments), phenothiazines, carrots
    7. Clarity – how clear is the sample?
    8. Cloudy – can be normal (especially in males), may also be bacterial infection (check the smell), WBC, lipids
    9. Frothy – this suggests proteinurea
    10. Is there anything in there that shouldn’t be in there?
    11. Make sure you keep the bottle on the tray, or trolley that it is given to you on! – e.g. in OSCE’s don’t lift it up and put it on the table!
  4. 4)      Open it and have a smell
    1. Ketones – smell like nail polish remover – diabetes
    2. Sweet smelling – remember the renal threshold – some people naturally excrete glucose in their urine. Other wise could be a sign of DM
    3. Foul smelling – bacterial infection, GI-bladder fistula
  5. Check your dipsticks:
    1. Are they in-date?
    2. Check silica gel crystals are present in the container to ensure the sticks have been kept dry
  6. Dip it – stick the stick all the way in, ensure all of the test areas have been in contact with the urine. Shake off the excess, and perhaps dab it on a paper towel.
  7. Wait the desired amount of time and note down the results. The time required for each inidivdual test is usually listed on urine diptick container – for example, leucocytes often require a 2 minute wait. The times down the side of the bottle are the time from 0, not the time between each result.
  8. Compare the strips to the colours on the reference sticker
  9. If in your exam – explain what irregularities are present, and what would you do to test them further
  10. Put the lid back on, put the sample back. Take gloves off (yellow bin) and wash your hands.

 Example of a Urine Dipstick chart

Urine Dipstick Results Chart Interpretation

Urine Dipstick Results Chart

Abnormal urine dipstick findings

Haematuria

  • Contamination from menstrual bleeding this is THE most common cause of ‘haematuria’!
  • Recent trauma
  • Prostate examination
  • Other recent urological examination (e.g. cystoscopy)
  • Glomerular or tubular pathology
  • Urologic pathology – this present with haematuria without proteinuria
  • Exercise induced – long distance runner. Result will be negative if repeated after 72 hours with no further exercise
  • Dehydration
  • Urine dipstick test is 90% sensitive, but less specific. However, only 0.5-6% of patients have significant underlying pathology

Proteinuria

  • Healthy adults excrete 80-120mg protein / day. This can be up to 1g per day.This usually occurs at night. This is generally too small of an amount to be detected on urine dipstick testing. The dipstick can detect 20-30mg / dl.
  • Proteinuria above normal levels on a urine dipstick may indicate; renovascular, glomerular or tubular interstitial renal disease, or it can be a sign of diseases that cause overproduction of urine, such as myeloma.
  • False negatives can occur when there is very diluted urine and / or when the primary protein is not albumin. They can also occur in very alkaline conditions.
  • Transient proteinuria – in young patients this is usually not a problem, and resolves within a few days, or after >8 hours lying down.  In older patients it may be a sign of congestive heart failure.
  • Intermittent proteinuria – can be present in young adults as a result of prolonged vertical posture, exposure to cold, pregnancy and hypertension. This usually produces about 1g of protein per day. This is asymptomatic, and should only ever be treated in renal problems are detected.
  • Persistent – due to underlying disease, most commonly; glomerular. This often produces in excess of 2g protein per day. Can also be due to overflow proteinuria (myeloma), connective tissue disorders, DM, hypertension.
  • Pre-eclampsia  – a condition in pregnant women characterised by hypertension and proteinuria.

Glycosuria         

  • Small amounts of urine are naturally excreted. The actual amount varies with the renal threshold from patient to patient. Generally these levels are too small to be detected on urine dipstick.
  • Can be caused by diabetes, Cushing’s syndrome, liver and pancreatic disease, Fanconi’s syndrome

Ketones

  • Diabetic ketoacidosis, pregnancy, after starvation and dehydration (often present in gastroenteritis / dehydration), rapid weight loss

Bilirubin and urobilogen

  • Normal urine contains no bilirubin, and very little urobilogen
  • Conjugated bilirubin may appear in the urine in the presence of liver disease, or bile duct obstruction.

Leukocytes

  • This test has lower specificity for infection than nitrites, and thus testing for nitrites is seen as for the presence of infection.
  • Be wary of diagnosing a UTI based of leucocytes only. In my practice (as a GP) in a well, asymptomatic patient I will often send these samples for MC+S without treating, to confirm if a UTI is present.
  • However, especially in the elderly, leucocytes only may indicate a UTI

pH

  • Should be between 4.5 and 5.3
  • A metabolic acidosis and alkaloid urine suggests a renal tubular acidosis. These patients have a risk of stone formation and nephrocalcinosis
  • Acidic urine can be caused by diet and uric acid calculi
  • Note that stale urine can become alkaline – thus you should check if the urine has been left fro any period of time

Nitrites

  • The presence of nitrites is essentially diagnostic for UTI
  • These re produced by bacteria; and thus raised levels indicate UTI. Accuracy may be affected in symptomatic patients, and patients on antibiotics.

Specific gravity

  • This shows the concentration of solutes in the urine; and is thus a measure of the ability of the kidneys to concentrate fluids.
  • If the value is high:
    • Dehydration
    • Glycosuria
    • Proteinuria
    • Renal artery stenosis
  • If the value is low

Finishing off

  • Consider FBC and U+E’s if there is any proteinuria, abnormal specific gravity
  • If glucose is present; do a random/fasting blood glucose, or a glucose tolerance test, or HbA1c. Refer onto diabetes specialist if required.
  • If protein is present; rule out benign causes (e.g. the postural cause, you could do an early morning urine sample, or you could to a 24hr glucose monitoring. Refer to renal specialist
  • If blood is present; send the urine sample to microscopy, refer to renal/oncology/urology
  • Bacteria; send for microbiology, culture and sensitivity (MC+S), and if symptoms present, then start on broad spectrum antibiotics. UTIs are most commonly cause by E. coli. Trimethoprim or nitrofurantoin are common first line choices for antibiotics – but check your local guidelines.

24 hour urine sampling

Indications

  • Volume –  water overload / depletion
  • total protein excretion – glomerular function
  • creatinine clearance – renal function
  • Cortisol – Cushings
  • Na/K – renal failure, aldosteronism / Conn’s syndrome
  • Catecholamines – phenochromocytoma

Procedure

  • Pick a start time, e.g. 9am. The patient should completely empty their bladder before they start
  • After this time, they should collect all their urine. They are often given two containers; a small one to urinate in and a larger one to collect it all in
  • If possible, urine should be kept refrigerated
  • at the end of the 24hrs, the patient should urinate and collect it one last time, before taking the sample for analysis as soon as possible

Results

  • Volume – normal production is about a minimum of 30ml/hour. In a 24 hour period you should be worried if the total volume is less than 500-600ml (technically 720ml/day is normal ‘minimum’)
  • Protein
    • <2.0g – may indicate tubulointerstitial problems
    • 2.0-3.0g – this is considered in the normal range                              
    • >3.0g – may indicate nephrotic syndrome

 

 

 

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