Urine test strips

Urine Test Strips ~ What do they detect?

urine test strips what do they detect

What are URS urine test strips

Urine test strips are a well established first line screening tool in global healthcare. But why are they so universally used, and what can they detect when used in apparently well individuals.

The reagent technology imbedded into the pads on the urine test strips have not changed in 50 years, although the development of a dry pad placed in a standard series on a plastic strip only became widespread in the mid 20th Century. Prior to this clinicians used wet chemical agents to detect abnormalities in urine samples, a time consuming and expensive process.

Dry reagent technology revolutionised the dip testing of urine samples for a range of parameters, the best established being sugar, specifically glucose, with the added advantage of being able to establish a level range by comparing the pad colour change against a standard reference chart at a specified time.

What do urine test strips test for?

Glucose is not normally excreted in urine, if it is, then it is a marker of high blood glucose levels and the development of insulin resistance and diabetes. This process normally takes years before symptoms prompt investigation and by detecting glucose in an asymptomatic patients urine screen can reduce the complications and risks to end organs that may occur prior to symptomatic diagnosis.

Ketone bodies in urine can also be a marker of diabetes and in particular keto-acidosis associated with very high glucose. Ketones can still be used as a marker for poorly controlled diabetes, but this has mainly be replaced with blood test strip measurement of ketone levels in real time. Today urine ketones are more likely to be of interest to individuals modifying their diet to burn fat and excrete ketones as a marker of carbohydrate restriction, the classic keto-diet.

Blood in urine is never a good finding. The sensitivity of urine test strips enables the detection of microscopic levels, not visible to the naked eye. The medical term for this is microscopic haemoturia. The least concerning cause of blood in the urine is a urinary tract infection, this can be distal, as in a urethritis or std, bladder as in cystitis or renal as in kidney infection or pyelonephritis. Other causes include renal stones, post medical procedures, renal tumours, bladder polyps or trauma.

Protein should not normally be excreted in urine. Causes include infections and renal diseases. There are also a few rare metabolic conditions where excess abnormal protein strands are excreted into the urine. On its own without positive blood or Leucocytes in the same sample suggests renal disease, leaky kidneys.

Leucocytes or white blood cells in urine suggests infection somewhere in the renal tract. It is one of the key markers for infection and will often be accompanied with a positive nitrite and protein test, and if severe blood may also be detected in the same sample.

Specific Gravity is an indicator of the concentration of the urine sample and there is a large variation over the course of a 24 hour period depending on fluid input. As such, it is not a very specific marker but helps in the interpretation of the results indicating if the sample is dilute or concentrated, ie as a marker of dehydration.

pH or acidity markers again can indicate metabolic conditions or renal disease including kidney stones. Dietary factors can also affect the pH of urine. A normal urine pH is between 4.8 and 8.1 

Nitrite is a bacterial breakdown product of Nitrates and if positive tends to indicate an infection. It is a key indicator for Renal Tract Infection with blood and leucocytes.

Bilirubin is not normally found in urine and is an indicator or Liver disease. Bilirubin will normally cause yellow discolouration in the whites of the eye before it causes full clinical jaundice. Liver diseases like Cirrhosis  and Liver failure can elevate bilirubin levels. Blood disorders resulting in high cell turnover and breakdown can also overwhelm the liver, elevating bilirubin blood levels and renal excretion.

Urobilinogen is found in trace amounts in urine, but more than 0.2mg/dl is abnormal and indicates Bilirubin is being degraded in the gut, again an indicator of Liver disease or blood disorders with high cell degradation rates.

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