Introduction
Where kidney disease is common but diagnostic facilities are limited and expensive, examining the urine is a cheap and effective method for enhancing the diagnosis of kidney disease. It can also identify evidence of systemic disorders such as diabetes mellitus. One of the joys of practising nephrology is that the ‘substrate’ of the kidneys - urine - is (usually) freely available, easy to collect and very informative as to the underlying pathology in the kidney. All patients with suspected kidney disease should be asked to submit a urine sample for examination and should be questioned about the urine they are passing - the latter is frequently neglected by physicians but can be just as important as a physical examination of the urine itself.
History - the right questions to ask
Most people will be familiar with their frequency of micturition and the appearance of the urine they produce - changes in these parameters can reflect kidney or systemic disease. Routine questioning about the passing of urine can add to the clinical assessment of kidney disease before the urine is examined (see Table 1).
Table 1.
Symptoms of abnormal micturition and associated pathological conditions
| Parameter | Symptoms | Associated conditions |
| Frequency | Polyuria (increase in quantity and frequency) Oliguria (reduced urine volume and frequency) |
Diabetes mellitus and diabetes insipidus. Severe kidney failure when tubular concentrating ability is reduced Volume depletion (e.g. diarrhoea and vomiting) Renal tract obstruction (e.g. stones, malignancy) Severe intrinsic kidney disease -either acute or chronic (e.g. diabetes mellitus, glomerulonephritis, vasculitis) |
| Odour | Offensive odour | Urinary tract infection Very concentrated urine e.g. due to volume depletion |
| Colour (see table 2 for more detais more details) |
Pale urine Dark urine Visible haematuria |
Diabetes mellitus and diabetes insipidus Excessive water consumption Volume depletion resulting in concentrated urine Infection, pigments or inflammation Schistosomiasis, malignancy, calculi, infection, factitious |
| Painful micturition | Dysuria, flank pain, renal colic |
Infection, stones, trauma, cyst pathology in polycystic kidney disease |
| Other | Frothy urine | Heavy proteinuria (proteinuria reduces the surface tension of urine causing frothing) |
Abnormalities of urine and micturition must be put into context with the remainder of the history. The age of the patient, duration of symptoms, recent environmental exposures and an occupational history should all be elicited. In patients over 40, a history of visible haematuria must prompt investigation for renal tract malignancy. Visible haematuria occurring 1–7 days after an upper respiratory tract infection (synpharyngitic haematuria) is almost diagnostic of IgA nephropathy. In children, the same phenomenon occurs after a recent Strep or Staph infection but the haematuria can occur up to 3 weeks after the initial infection and is indicative of post infectious glomerulonephritis.
In experienced hands, inspecting the urine in a sterile container at the bedside can yield useful diagnostic information before a urine dipstick or microscope are required. Visibly confirming the patient's reports of the urine colour will enhance the diagnostic process. Collect approximately 10 mls of urine in a sterile container and examine freshly at the bedside, preferably using natural light to illuminate the sample. Urine that is left to stand can become discoloured or cloudy.
Urine examination - visual inspection
Different disease entities can yield typical discolouration of the urine (see Table 2) but apparently normal looking urine at the bedside can contain numerous abnormalities on further examination.
Table 2.
Colouration of the urine and potential causes
| Appearance of urine | Potential cause |
| Pale - same colour as water | Diabetes mellitus or diabetes insipidus, excessive water consumption |
| Orange tinge | Treatment with rifampicin (can be used to assess drug compliance) |
| Cloudy | Bacterial infection, old sample of urine |
| Red discolouration and cloudy | Schistosomiasis, renal tract malignancy or stones, bacterial infection, factitious (addition of blood to the urine by the patient after urine is passed) |
| Brown and cloudy (also known as rusty urine) |
Acute glomerulonephritis, malaria with haemaglobinuria, rhadomyolysis (tissue trauma causing myoglobinuria), other causes of intravascular haemolysis |
| Yellow-brown or green discolouration | Due to the presence of bilirubin from liver disease (hepatitis, obstruction, toxins) |
| Milky white (chyluria) | Obstruction of lymphatics caused by filariasis |
Urine dipstick analysis
If a patient with suspected kidney disease has produced urine for examination and a dipstick is available, it is reprehensible not to use it to analyse the urine. Vital diagnostic information in cases of both acute and chronic kidney disease can be obtained which will assist with diagnosis, inform treatment decisions and monitor response to therapy. Few other bedside tests in modern medicine can yield such a large volume of information for such a low cost.
There are a range of dipstick tests on the market which provide a variety of diagnostic information - some more limited than others. Some dipsticks will test for a more limited range of abnormalities and a “normal” test result on a limited dipstick may be falsely reassuring if the desired urine abnormality is not detected by that dipstick. Each manufacturer will specify how long the dipstick should be immersed in the urine and how many seconds should elapse before a final decision about the presence of a particular abnormality is made. Confirming the correct storage of urine dipsticks and that they have not expired is an important step for clinicians.
Each colour block on a urine dipstick is impregnated with chemicals relevant to that test which will change colour if the particular abnormality is present. The dipstick must be held up against its container to assess change in colour blocks. As with any assessment of urine, the test findings must be put into context with the history, examination and other investigations. Table 3 describes a range of common dipstick assessments and important associated abnormalities that should be considered by clinicians.
Table 3.
Important abnormalities on urine dipstick analysis and their clinical significance
| Abnormality | Clinical significance |
| Proteinuria | Glomerular disease, overflow proteinuria from the blood, transient febrile illness |
| Blood(will detect red cells and haemoglobin) |
Glomerular disease, intravascular haemolysis, calculi, tumour, infection, menstruation |
| pH | Normal urine pH is 5–7. Alkaline urine reflects urinary tract infection |
| Glucose | Diabetes and proximal tubular dysfunction e.g. Fanconi's syndrome |
| Ketones | Diabetic ketoacidosis |
| Leucocytes | Infection, calculi, interstitial nephritis (eosinophils in urine) |
| Nitrites | Bacterial infection |
| Specific gravity | Normal SG is 1.010. Higher values reflect concentrated urine such as in volume depletion |
Urine microscopy
If a microscope and centrifuge are available, a fresh urine sample should be examined for more detailed abnormalities which can add diagnostic value. Findings on microscopy can enhance the understanding of the pathophysiology of the underlying condition that may be suggested by other steps in the analysis of urine.
Technique for urine microscopy
Obtain a fresh, mid stream urine sample and analyse within 2 hours of collection.
Decant 10mls into a sterile container suitable for a centrifuge.
Centrifuge at 500-100g for 5 minutes.
Remove the supernatant by pouring down a sink
Visually inspect for any sediment.
Tap the centrifuge tube to thoroughly mix remaining sediment and urine.
Place one drop on a standard slide and cover with a cover slip.
Examine under a microscope at x10 and x40 power.
Specialist microscopy skills are required to examine urine and where such expertise is present, this analysis should be performed. The key abnormalities that will aid clinicians are the presence of cells, casts and crystals (see Table 4).
Table 4.
Microscopic examination of urine deposit after centrifugation
 |
Other tests for urine samples
Pregnancy can be confirmed by a urine HCG test. Further biochemical studies such as electrolyte values, osmolality and more accurate quantification of proteinuria among others may be possible in more advanced laboratories.
Urine culture should be considered if bacterial infection is suspected to guide antibiotic therapy.
Summary
Urine is a window to understanding diseases of the kidney and systemic disorders. It is the easiest bodily fluid to obtain and can be analysed in resource limited settings where it is of great value in enhancing diagnostic and therapeutic pathways. Asking questions about urine and urination in each clinical history and routinely analysing the urine at the bed-side are skills that all health professionals should have and, equally importantly, should use.
Further useful Reading
Parry EHO (Ed) Principles of Medicine in Africa. Cambridge University Press. 4th Edn 2010.
Wilson LA. Urinalysis - a nursing perspective. Nursing Standards 2005; 19(35):51–54.
Steddon S, Ashman N, Chesser A, Cunningham J (Eds). Oxford Handbook of Nephrology and Hypertension - (from the Oxford Handbook series). OUP 2006