Friday, August 24, 2007


Subject Title: Clinical Chemistry
Name of Test: Urine specific gravity

The specific gravity of urine indicates the relative proportions of dissolved solid components to the total volume of the specimen. It measures the concentrating and diluting abilities of the kidney. Water has a specific gravity of 1.000. Since urine is a solution of minerals, salts and organic compounds in water, the specific gravity is greater than 1.000. The more concentrated the urine, the higher the urine specific gravity. Knowledge of the specific gravity is needed in interpreting the results of most tests performed in routine urinalysis. Specific gravity is measured using the refractometer and is determined by the principle of refractometry.

A refractometer

Principle of Test
An indirect method of measuring specific gravity is refractometry. The refractometer does this by measuring the refractive index of the solution. The refractive index of a solution is related to the content of dissolved solids present. It is the ratio of the velocity of light in air to the velocity of light in solution. This ratio varies directly with the number of dissolved particles in solution. The refractometer utilizes a light source, which pass through a chamber containing the specimen and a prism with scale readings. There is a direct relationship between the reading of the degree of refraction of light and the concentration of the specimen. This reading can be converted to specific gravity. Scale readings are in terms of specific gravity, refractive index and serum or plasma total protein. In my lab, we do not use refractometer to measure the total protein of patient sample but use Roche Modular analyzer to measure it. The refractometer is compensated to give correct readings on aqueous solutions at all temperatures ranging from 15°C-37°C. Readings need not be adjusted for either the temperature of the sample or the temperature of the room in which the refractometer is used.


Before running any patient samples, we must first do quality control. In my lab, we use KOVA liqua-Trol level 1 (normal) and KOVA liqua-Trol level 2 (abnormal).

1) Label the test request form, urine container and a test-tube

2) Pipette a few ml of random urine into the labeled test-tube

3) Add a few drops of distilled water into the coverslip of the refractometer and clean it using gauze, ensuring the coverslip and prism are clean and dry

4) Add few drops of urine into the coverslip, making sure that no air bubbles are trapped within.

5) Read the specific gravity using the urine specific gravity scale. Avoid lifting the coverslip before the reading is made

6) Record the result on the test request form, which will be later keyed into the LIS

7) Add few drops of distilled water into coverslip again for washing off the urine and dry it using gauze. It is important that the refractometer is always maintained in a clean state

Reference Range

Normal values range from 1.003-1.030 but average is between 1.010 and 1.025. Specific gravity is highest in the first morning specimen, which is usually greater than 1.020 but not exceeding 1.030, due to the highly concentrated urine.

Clinical Interpretation
Low Specific Gravity
Diabetes insipidus, a rare disease caused by impaired functioning of the antidiuretic hormone (ADH), is the most obvious and severe example of the loss of effective concentrating ability of kidneys. This disease is characterized by large volume of urine with low specific gravity. Specific gravity in such case usually ranges between 1.001 and 1.003. Low specific gravity can also occur in patients with glomerulonephristis and pyelonephritis. Pyelonephritis is an ascending urinary tract infection that has reached the pelvis of the kidney. In these diseases, the kidney has lost its ability to reabsorb water due to tubular damage. Thus urine remains dilute. Urine with a fixed low specific gravity is indicative of severe renal damage with disturbance of both the concentrating and diluting abilities of the kidney.

High Specific Gravity
Specific gravity is high in patients when there has been excessive loss of water, as with
sweating, fever, vomiting and diarrhea. Increased secretion of ADH will cause increased tubular water reabsorption and decrease in urine volume. Hence it will have high specific gravity. Trauma, stress, infections, surgery and many drugs cause increased in ADH secretion. Moreover, abnormally high amounts of some of the urinary constituents, in particular glucose and protein, can increase specific gravity.

Urine specific gravity is used for monitoring of diseases and we can use urine osmolality test to further confirm the results. Osmolality is a more exact measurement of urine concentration as specific gravity depends on precise nature of the molecules in the urine and requires correction for the presence of glucose and protein. Urine specific gravity is easy and convenient to test.

Soong Ci Liang

Sunday, August 19, 2007


Subject: MMIC
Topic: Reading of urine cultures

Some of the properties that can be used to identify the organisms
· Colony appearance (colour and shape)
· Ability to ferment lactose
· Ability to haemolyse red blood cells
· Ability to produce cytochrome oxidase

Lactose Fermentor (LF) Vs Non-Lactose Fermentor (NLF)

Able to utilize lactose on CLEDUnable to utilize lactose on CLED
Forms white to grey colonies on BAP but forms yellow colonies on CLEDForms white to grey colonies on BAP and CLED
Produces acid causing CLED to turn yellowMay produce alkaline causing CLED to turn blue


Some organisms are able to cause the lysis of the sheep red blood cells found on BAP. Haemolysis can be detected through holding up the back of plate against a source of light.

Haemolysis on BAP can be classified into two categories:
• α-haemolytic
o greenish-looking colonies
• β-haemolytic
o forms a clearance around the colonies

Oxidase Test
The oxidase test checks for the production of cytochrome oxidase (an enzyme). The oxidase reagent contains a compound that changes color when it becomes oxidized (i.e. chromogenic reducing agent).

A drop of oxidase reagent is dropped onto the test strip. The test strip is then used to lightly touch the colonies.
Positive: Blue (cytochrome oxidase present)
Negative: No colour change

Identification of Microorganism

MicroorganismColony AppearanceFerment LactoseOther Properties
Escherichia Coli• Flat, grey colonies on BAP
• Form yellow colonies on CLED
Klebsiella spp.• Mucoid, convex colonies
• Form white colonies on BAP
• Form yellow colonies on CLED
Streptococcus spp. (GPC)• Small, white colonies on BAP
• Form yellow colonies on CLED
Yes• Catalase negative

• α-haemolytic:
eg. Streptococcus pneumoniae

• β-haemolytic:
Streptococcus group A, B etc

• Non-haemolytic:
E.g. Enterococcus spp.
(Greyer appearance)
Staphylococcus spp. (GPC)• Small, white, flat colonies on BAP
• Form yellow colonies on CLED
Yes• Catalase positive
• Can be hemolytic positive or negative
Pseudomonas spp.• Swarms on BAP
• Spready colonies on CLED
No• Pungent smell
• Oxidase positive
• Swarming ability
Proteus spp.• Swarms on BAP
• Glossy
No• Pungent smell
• Swarming ability
Candida spp.• Small, flat, white colonies on BAP and CLED
• Slightly spready
• Not glossy

E. Coli

Klebsiella spp.

Pseudomonas and Klebsiella spp.

Proteus spp.

Candida spp.

Boon Ching

Sunday, August 5, 2007


I have been attached to Haematology lab for three weeks. Normally, i performs routine tests like FBC, PBF, ESR and other miscellanous tests like dengue serology test and malaria parasite screening. erm.. so here i will elaborate on the dengue serology test.

Dengue Serology Test

It is performed to obtain a qualitative presumptive detection of IgG and IgM antibodies, as well as a presumptive differentiation between primary and secondary infection.

Serum antibodies of the IgM/IgG class, when present, bind to the anti-human IgM/IgG immobilized in 2 lines across the test strip. The colloidal gold-labeled antiflavivirus monoclonal forms complexes with the dengue antigen that is captured by dengue specific IgM/IgG in the patient’s serum. These complexes are visualized as pink/purple line(s).

Sample requirement
- At least 1ml of capillary/venous blood collected in plain tube
- Centrifuge the sample at 3000 rpm for 10 minutes
- Sample serum should be preferably clear, non-haemolysed, non-lipaemic and non-icteric.

Use the Denge Duo IgM and IgG Rapid Strip Test Kit (PanBio)
Pipette 10μl of the serum onto the strip kit and the result is to be viewed after 15 minutes. Before conducting this test, the kit is kept in the fridge and so when this test is requested, we have to take it out and keep it in the room temperature for 10-15 minutes.

Dengue results are reported in LIS as follows:

Results Interpretation

Control positive only
If dengue infection is strongly suspected, consider PCR for dengue virus. Within 1st 5 days of illness. If this is an acute specimen, PCR can be performed on the sample, which has been retained in the lab.

IgM and Control positive
Consistent with 1° dengue. Occasional false positive may occur in certain infections such as measles.

IgM, IgG and Control positivie
Consistent with 2° dengue

IgG and Control positive
Consistent with 2° dengue. Cross reactivity may occur with flavivirus.

Primary (1°) infection is characterized by the presence of detectable IgM antibodies 3-5 days after the onset of infection.
Secondary (2°) infection characterized by the elevation of specific IgG antibodies 1-2 days after the onset of infection and in the majority of the cases this generally accompanied by an elevation of IgM.

that's all for this entry. enjoy reading. take care all man. enjoy ur SIP. =)

Doreen (tg o1)