How to 'read' urine colour
Urine can be a valuable clue in health deduction. As one of the body's core four ways of eliminating waste products (the others being breath, faeces, and sweat), changes in appearance, smell, and flow, can often pinpoint the location and diagnosis of new disease. This can direct further investigation when a doctor understands what they see. For this article, we will concentrate on the information you can 'read' at a glance from the appearance of urine.
Clear: clear urine suggests dilution. It can be a normal variation when someone is well hydrated. When excessive urination and thirst is present, it may be caused by an inability to concentrate urine eg diabetes insipidus, or an expected side effect of diuretics such as caffeine or 'water pills', the latter which are commonly used for hypertension (raised blood pressure), or heart failure.
Straw yellow: urine's normal colour. The yellow tinge results from small amounts of the pigmented substance urobilin, a breakdown product of old blood cells.
Orange: The body will concentrate urine to a darker yellow, orange, or brown when you are dehydrated. This is the result of fluid intake not matching fluid losses (usually via sweat, diarrhoea, vomiting, or urination). Often it is noticed after intense activity where fluid lost through sweat is not replaced adequately by drinking.
Brown: the urine may be dyed by high concentrations of breakdown products from old blood cells. Causes include:
- increased blood breakdown: eg haemolytic disease, where more bilirubin is released into the bloodstream
- reduced bilirubin processing: eg liver inflammation in infection like Hepatitis C
- post-hepatic obstruction: strongly suggested when brown urine is seen in combination with pale stools. Bilirubin normally stains faeces brown, and so this indicates something is obstructing entry into the bowels, between bilirubin production in the liver, and deposition in the small bowel a few cm later. The culprits are usually gall stones, and cancer of the pancreas or bowel. This forces re-absorbtion into the blood and filtering out of the body via the kidneys in the urine as urobilin. The increase in urobilin excreted in the urine darkens it (illustrated explanation below).
Red: This may represent blood in the urine (eg from infection, renal stones, tumours), or red staining from dyes in food (eg beetroot) or drugs (eg Rifampicin). For a more extensive illustrated look at causes of blood in the urine, check out my haematuria article.
Blue/green: contrast medium is used in some medical scans, and may temporarily colour urine blue/green. Other culprits include a genetic condition called familial hypercalcemia (aka blue diaper syndrome), and an atypical urine infection from pseudomonas bacteria.
Cola: brown/black urine suggests myoglobin is present in the urine. This is a substance normally found concentrated in muscle cells as a reserve of oxygen. It is released when muscle cells are damaged or destroyed; a process called rhabdomyolysis. Common causes include major trauma and crush injuries in vehicular accidents. Another precipitant seen more in the elderly are 'long lies' when someone has fallen and cannot get up for hours or days. Sudden increases in myoglobin filtering by the kidneys can damage them and result in fast deterioration. The tell-tale dark urine may be the first clue that someone is about to get more unwell (assuming they weren't in a road accident, which would have been an earlier and more obvious clue).
Some other helpful clues you may see in urine:
80% of renal calculi (stones) are composed of calcium compounds eg Calcium Oxalate. These cause pain as they are hard, sometimes sharp, and are being squeezed through a piping system designed to accommodate fluids only. They can cause trauma and bleeding as they are passed, or if they become stuck can result in serious infection, and damage to the kidney above the blockage. If you see one that has passed, there may be more.
Bubbles / faeces
High protein content may make the urine bubbly. This can be seen in renal disease where there is excess leakage through damage to this filtering organ.
The bladder is a closed system with no air, and so there should not be gas in the urine. An abnormal connection between the bowel and bladder known as a fistula, can result in faeces and air (flatus) in the urine. This may cause recurrent infections. Fistulas can develop when there is inflammation of the bladder or bowel at a point they are touching, eg caused by infection, cancer, or previous surgery.
Note: soap and other cleaning agents on a loo may make bubbles as you pee, as can simply the impact of urine into toilet water at pressure. Always interpret signs in context!
Cloudy urine, that may be darker, or more strongly smelling, suggests infection. Symptoms may include urinary frequency (a need to pee more often), dysuria (burning/stinging when peeing), and pus discharging from the urethra. Infection is more common in women due to a shorter urethra for bacteria to climb from the outside world to the bladder. Also contributing is the anatomical proximity of the urethra to the anus (and thus faeces). This is why wiping from front to back is important for hygiene, so faecal bacteria are not brought into contact with the urethra.
Clots suggest bleeding, which may arise from the urinary system or gynaecological organs in women. Bleeding in the urinary tract is covered in this article.
There's a lot you can deduce about health from the appearance of urine. Changes and context are important to interpret what you see (eg dark urine after playing sports without drinking is more likely caused by dehydration than haemolysis).
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