Saturday, 26 July 2014

Investigations, Investigations, Investigations (Part 1)


Image courtesy of [anankkml] / FreeDigitalPhotos.net

The cornerstone of medicine remains the classic history and examination- let the patient tell their story, and the physician's hand of assessment can help pinpoint the diagnosis.

However, when diagnoses are unclear or can't be differentiated, that's where investigations come in. Sadly, today they're often over-used, but when used appropriately they offer a wealth of information that can help tailor all important management and get the patient on the path to recovery faster.

This multi-part post will take a look at some of the common investigations performed, what they can tell us and the reasons why and when they should be used.

PART 1- urine



It's amazing how much information we can obtain from the humble urine sample. Even before we had all the fancy urinanalysis testing we have today, we could diagnose diabetes (though I am not an advocate of returning to the days when doctors had to taste urine for sweetness in order to do this!)

Some of the commoner tests we can do include:

Pregnancy test


Image courtesy of [sattva] / FreeDigitalPhotos.net

This is possible thanks to a substance known as beta human chorionic gonadoptrophin, which is secreted from the early placenta after implantation of a fertilized egg. It's also very specific (as it's extremely rare for this substance to be found outside of pregnancy, although other causes exist, such as certain testicular tumors). Now widely available in various guises over the counter, it's a great quick and accurate test.

This chemical can also be measured in blood, and comparing numbers can help in the management of miscarriage and ectopic pregnancy (more on this in the next part)

In a medical context it's extremely useful, as if a woman of reproductive age presents with abdominal pain we can use it to exclude an ectopic pregnancy, which can have life-threatening consequences if not picked up early.

Urine dip


Urinalysis - Measurement

From a tiny stick coated with various reactants, we can diagnose if particular substances are in the urine, such as protein, glucose, blood, leucocytes (white cells, the cells that fight infection) and nitrites (an indicator for infection in the urinary tract by some bugs).

Of course, as stated above, the reason for doing the dipstix will govern how to interpret the results (e.g. a lady presenting with burning pain on passing urine, or a man complaining of blood in the urine, or a boy with kidney problems that means protein is leaking out when it shouldn't). It can also be the earliest sign of kidney disease and other systemic diseases. Quick and easy to perform, it's perhaps one of the most useful bedside tests we have.

Further reading:

1. http://imc02.hccs.edu/BiologyLabs/AP2/07Urinary/07UrinalysisIndex.html

MSU (mid stream urine)/ urinanalysis

If the dipstix shows something in the urine, it's usually sent on for this test. This is where the sample is sent to the lab and they look under the microscope for signs of infection, signs of inflammatory changes or 'casts', and if they can grow any bugs. If bugs are grown, they can then test which antibiotics work against it, which is extremely useful as it means we can make sure the patient is on the right antibiotic to clear the infection.

24 hour collection tests



These are more specialised tests, often done in a hospital setting. The common ones are protein excretion, VMA (a chemical secreted by a type of adrenal tumour), and cortisol (the natural 'steroid' hormone). These can be quite difficult to perform, though, as they require accurate collecting of urine, avoidance of temperature distortion, and it takes time to process results.

Further reading:

1. http://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=92&ContentID=P08955

2. http://www.healthline.com/health/24-hour-urine-protein#Overview 1

So, as we can see, urine is a very useful bodily sample that can diagnose a range of conditions!

Next time, part 2 will look at the next most tested body fluid, blood.

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