WEEK 13

For the past 3 weeks, I was posted to a satellite laboratory under the company I was attached to. A satellite lab basically means a smaller “branch” that carries out basic tests for walk-in patients. The satellite lab also receives samples from next-door clinics and a nearby hospital. It is more stressful in the morning as most of the samples are urgent samples, compared to the main lab.

On my last week there, I was assigned the task the carry out urine tests. Urine tests include urine pregnancy tests, urine glucose tolerance tests and urinalysis. For this entry, I shall talk about urinalysis.

The equipment used in the lab is Miditron Urine Analyzer manufactured by Boehringer Mannheim. It is actually quite an old equipment but it produces results within 5 minutes. The whole process is semi-automated. Upon receiving urine samples, the urine need to be transferred into a long conical tube up to the first marking from the top. The patient’s barcode number is registered into the machine for easy identification, results entry and results validation later on, which can only be done by the permanent staffs there. The urine is checked for its colour and clarity. The colour may be yellow, straw, reddish, or dark brown. The clarity ranges from clear to turbid. A test strip is then dipped into the urine. The test strip used is known as Combur 10 Test M manufactured by Roche Diagnostics. After dipping the test strip into the urine, the test strip is loaded into the machine. The machine then scans the test strip to read for any colour change on the test strip. After scanning the test strips, results are produced and printed about 5 minutes later.

By using the test strip, the specific gravity, pH, presence of leukocytes, nitrite, protein, glucose, ketone bodies, urobilinogen, bilirubin, and erythrocytes can be tested.

Principles:

- Specific Gravity : detection of ion concentration of the urine through a colour change from blue to blue-green or yellow when protons are released by a complexing agent.
- pH : contains pH indicators methyl red, phenolphthalein and bromothymol blue which reacts with hydrogen ions to produce a colour change.
- Leukocytes : granulocyte esterases cleave off indoxyl ester which reacts with diazonium salt to produce a violet dye.
- Nitrite : detection of organic nitrite compounds produced by nitrite-forming bacteria. Presence of nitrite will cause a colour change to pink or red.
- Protein : this component is very sensitive to albumin. Detection of albumin is based on protein error of a pH indicator. Presence of protein in high amounts may indicate presence of casts, for example hyaline casts or granular casts.
- Glucose : reaction between glucose and oxidase or glucose and peroxidase.
- Ketone bodies : detection of ketone bodies and is more sensitive to acetoacetic acid than acetone.
- Urobilinogen : reaction between diazonium salt with urobilinogen present in the urine, producing a colour change to red.
- Bilirubin : (similar to urobilinogen) reaction between diazonium salt with bilirubin to produce a pinkish colouration.
- Erythrocytes : reaction between organic hydroperoxide with haemoglobin and myoglobin to produce a peroxidase-like reaction. Positive results would show a blueish-green colouration.

After running the urinalysis using the machine, the positive urine samples are centrifuged at 2500 rpm for 5 minutes to obtain the sediment. The sediment is then observed under a microscope which is usually done by a more senior medical technologist. However, I have been given a chance to observe certain bacteria, casts and crystals that are present in abnormal urine samples. Some crystals are quite common such as Calcium Oxalates, Uric Acid, Amorphous Phosphates and Amorphous Urates. Uric acid is usually present in urine samples with pH 5. Amorphous Phosphates and Amorphous Urates look very similar. Therefore, if they are present in a urine sample, the pH of the urine is usually looked at to differentiate between the two. Amorphous Phosphates are present in urine sample with pH 7 or more, while Amorphous Urates are present in urine sample with pH lesser than 7.

Nur Azeimah
0607060A
TG 02

7 comments:

  tg01 group 2

September 25, 2008 at 9:16 PM

i would like to know how are Calcium Oxalates appear under the microscope? how do you determine that particle is Calcium Oxalates?

From Ivan
TG01
0605070B

  Fluid collectors

September 26, 2008 at 1:13 PM

Hi Azeimah

Under the microscope, how do casts and crystals look like? Any distinct features? How do you differentiate the common crystals? If can, include some pictures.

Thanks!

LeeJin
TG02

  'Z'h'a'o'R'o'n'g'

September 26, 2008 at 2:17 PM

YoYo!

What does a high/low specific gravity result means?

What does it reflects about the patient's medical condition?

Tan ZHao rong
tg01

  hellomedtech

September 26, 2008 at 3:20 PM

This comment has been removed by the author.
  hellomedtech

September 26, 2008 at 3:22 PM

Hi

i would like to know how and why casts and crystals are formed in urine?

thanks =)

Nur Farhana
0604834B

  SIP

September 26, 2008 at 3:45 PM

hey Azei!

Do you spin ALL the urine to obtain the sediment to read under microscope?

For my lab we read the urine as it is.. only if we need to observe for casts then we spin to read the sediment:)

And just curious how does your lab report the results? is it generally like 'RBC present'?

Coz my lab we have to report in numbers like '15 RBCs seen'.. But if you are using the 'sediment' results wont it be inaccurate coz the sediment is concentrated?

THANKS!
P.s: Hope my qns are too tough coz i realise the above qns are quite hard to ans:p

Cheers,
Huimin
TG01 =)

  group1

September 26, 2008 at 4:01 PM

HI!

o.O this analyzer is so good. in my lab, i have to conduct these tests manually or on diffeent analyzers (one by one).

anyway, just to check, the results shown on the test strips only indicates the presence and absence of leukocytes, nitrite, protein, glucose, ketone bodies, urobilinogen, bilirubin, and erythrocytes or can it also indicate the different concentration of each component?

how does the doctor order thses test? just indicate urinalysis or they have to indicate what test they want?

Thanks
YuMei
TG01