Unravelling Green Urine: A Clinical Conundrum

By Syed Bilal Hashmi, Muhammad Umer Naeem Efendi, Sibtain Ahmed

Affiliations

1. Department of Pathology and Laboratory Medicine, the Aga Khan University, Karachi, Pakistan

doi: 10.29271/jcpsp.2025.12.1636

Sir,

Urine is a biological fluid that provides diagnostic information through its complex biochemical composition. The colour, odour, and volume of urine provide essential diagnostic details about a person's fluid balance and clinical status. Any variation in normal urine colour can be alarming for clinicians.¹ Green- coloured urine is an unusual but a visually alarming finding that may raises concern for underlying pathology. It is typically caused by exogenous factors such as medications, dyes, or infections. While often benign, this discolouration warrants careful evaluation to prevent unnecessary investigations and to correctly identify the causes, such as methylene blue administration.² The normal colour of urine ranges from light yellow to dark amber, and it is influenced by its solute concentration.³ Several factors can influence the colour of urine, including the presence of red blood cells, bilirubin, and certain medications.

Table  I:  Urinalysis  findings  of  the  patient  with  methaemoglobinaemia.

Parameters	Results
Colour	Green
Appearance	Clear
Specific gravity	1.020
pH	7
Protein	1.5 g/L (3+)
Glucose	Negative
Ketone	0.5 mmol/L (1+)
Urobilinogen	17 mmol/L (1+)
Bilirubin	Negative
Blood	50 /Ul (3+)
Nitrite	Positive
Leucocyte esterase	25 /mL (1+)
Red blood cells	06 /HPF
Leucocytes	01 /HPF
Bacteria	Few /HPF
Yeast	Nil
Crystals	Nil
Casts	Nil

Figure  1:  Green  urine  of  the  patient  with  methaemoglobinaemia.

Herein, the authors reported a rare case of a 60-year female patient who underwent a detailed urine analysis test. Urinalysis showed green-coloured urine (Figure 1), significant proteinuria, presence of blood, and positive nitrite (Table I). Upon reviewing the patient's clinical history, it was revealed that she was a known case of methaemoglobinaemia, a rare pathological condition in which the iron in haemoglobin is oxidised from its functional ferrous form to the non-functional ferric form.⁴ As part of the management of her condition, the patient had received methylene blue one day prior to the urine analysis. Methaemoglobinaemia may be congenital (e.g., cytochrome b₅ reductase deficiency) or acquired due to exposure to oxidising agents. Methylene blue, a water-soluble dye that works primarily by converting methaemoglobin (Fe³⁺) to its functional, reduced form (Fe²⁺) in individuals with methaemoglobinaemia. This transformation restores haemoglobin’s ability to bind oxygen, thus improving the delivery of oxygen to tissues.⁵ Methylene blue is metabolised to leucomethylene blue (colourless) in the gut. When methylene blue combines with urochrome in the urine, a harmless compound is formed, which gives a green or greenish blue colour to urine. The degree of green colouration in urine is proportional to the dose of methylene blue. Green discolouration of urine can be caused by other medications, such as propofol, indomethacin, promethazine, metoclopramide, cimetidine, and amitriptyline.⁶ The observation of green urine following the use of methylene blue, while intriguing, holds minimal clinical significance. However, physicians and laboratory professionals must be aware of this effect to prevent un- necessary investigations and avoid misinter- pretation of the findings.

COMPETING  INTEREST:
The  authors  declared  no  conflict  of  interest.

AUTHORS’  CONTRIBUTION:
SBH: Conception and design of the study, acquisition, analysis, and interpretation of data.
MUNE, SA: Drafting and critical revision of the manuscript for important intellectual content.
All authors approved the final version of the manuscript to be published.
 

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