Number of red and white blood cells in urine
Urine microscopy (on midstream urine, MSU)
Should show:
- Red blood cells (RC) <25 x10[6]/L
- White blood cells (WC) <5 x10[6]/L.
It is generally accepted that a RC count of 25 or less, or WC value of 5 or less, is not significant.
In other words, all humans have a small number of red and white blood cells in the urine. This is not surprising as 180L of blood are filtered by the kidneys daily.
Most stays in the blood as they cells are too large to pass through the 1 million tiny filters (called glomeruli) in each kidney.
Investigation of a patient with ‘microscopic blood on a urinary dipstick’
10% of the normal population have ‘microhaematruria’ on a urinary dipstick. Most are asymptomatic, and do not have a disease.
Why? The dipstick is notoriously over-sensitive for blood – i.e. many are false positives.
So. If your doctor discovers blood on a dipstick (and you have never seen blood), you should ask for an MSU. It is likely to be normal, in terms of the number of red cells in the urine.
If so, it then needs no further investigation.
Other resource
