Stout, pilsner or IPA: A craft beer review of urine colour

Urochrome or urobilin, together with urobilinogen, are degradation products of haemoglobin

Thinking I know everything about a certain topic has caught me out many times in the past. This often happens because you find that the “guidelines have changed, technology has advanced and previously held dogma is now relegated to the status of misconception.”

Like many things learned in detail, many years ago, the interpretation of urinalysis falls into this category and, according to US professor of emergency medicine and toxicology James R. Roberts, “should be revisited on a regular basis”. So, when was the last time you had a look at your pee?

As primary care and emergency physicians, we rou­tinely order urinalysis. Urine testing and microscopy are invaluable in the diagnosis of several genitourinary condi­tions, such as calculi or urinary tract infections, systemic disorders (eg, diabetes) and even malignancy, which can go unnoticed because it does not produce striking signs and symptoms. Many useful reviews have been published on the interpretation of the urine dipstick and the dif­ferential diagnoses of proteinuria and haematuria, but not many address the colours of urine, specifically, and we often just end up Googling: “What are the causes of green or orange urine?” I find the process of dealing with urine colours easiest when they are compared to beer. A variety of foods, dyes, medications, metabolic products and infections can also cause a prism of urine colours (see figure).

Normal urine should look like wheat beer, with its pale-straw colour. This yellow tinge is the result of a pigment called urochrome, or “the urochrome of Thudichum and Garrod”. Since 1798, when French chemists Fourcroy and Vauquelin first attempted to connect the yellow col­our of urine with the excretion of urea, various workers have speculated – with different results – as to its origin. Klemperer, in 1903, made the statement: “At present, I am inclined to believe that the urochrome is a direct de­rivative of the blood pigments and is synthesized by the kid­ney,” adding further that “an influence of the diet upon the excretion of urochrome has been observed”.

The last statement is im­portant because it is the only positive statement to be found in the literature with re­gard to the effects of diet. St Dombrowski gives an excellent historical review of the subject up to 1907. Today, we know that urochrome or urobilin, together with urobilinogen, are degradation products of haemoglobin.

Concentrated urine, compared to normal urine, pro­duces the hues of darker beers, like the saisons, IPAs or lagers – a common finding in the morning after overnight water restriction, and easily remedied (back to a wheat beer) by two or three glasses of water. Anything darker, such as a porter, red/brown/black ale, Guinness or stout, and “Houston, we have a problem”.

Shades of yellow and brown are not, however, the only colours with which urine can present. A variety of foods, dyes, medications, metabolic products and infections can also cause a prism of urine colours.

To close with, I once asked my father what older peo­ple do when they retire. He responded: “Make sure you have a chemistry background, and then one of the things you will enjoy most on retirement will be turning beer, whiskey and wine into urine.”

Melissa Yssel is a chemical pathologist at Wellington SCL

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