Labtech

Role of Laboratory in Early Diagnosis

The case for routine assessment of thyroid status is strongest in elderly who may have symptoms consistent with hypothyroidism.

Courtesy: Wellspring Chain of Laboratories

When a patient is referred by a clinician for thyroid tests, he may be symptomatic or asymptomatic. Clinician may be in need of immediate diagnosis, to confirm this as it is very crucial for thyroid test. It is here that a clinical laboratory plays an important role. The physician is dependent on the interpretation of the laboratory results to successfully diagnose and treat the patient.

The Importance

Thyroid function tests mainly include T3, T4 and TSH measurements. In the past five years, important changes have taken place in the strategy of thyroid function testing.

Dr Avinash Phadke

Previously, T3 (Total), T4 (Total) and TSH were the dominating tests. People believed that if T3 and T4 are low, then TSH has to be high and vice versa. But there are some factors that affect total T3 and T4, like proteins (TBG) (thyroid binding globulin). Hence it is the free hormone, called as Free T3 and Free T4, which are physiologically active. Worldwide, there is a trend for TSH and free T4 tests to replace the conventional Total T3, Total T4, and TSH for screening thyroid functions.

A slightly elevated total T4 concentration, compatible with hyperthyroidism, can occur with normal thyroid function if there is an increase in plasma binding protein, in this case free T4 may be normal.

Screening

Two to seven per cent of women over age of 40 years may have slightly elevated TSH concentrations. The case for routine assessment of thyroid status is strongest in the elderly population who may have symptoms consistent with hypothyroidism.

Chemiluminescence Assays

The last few years have seen the development and refinement of much new immunoassay measurement principles and systems.

• The development is more towards precise and reliable non-isotopic. Automated laboratory assays with detection limits measured in the picomolar or attomolar range.
• Chemiluminescent assays are now further modified in to electrochemiluminiscent assays.
• These assays are known to occur with numerous molecules including compounds of ruthenium, osmium, rhenium or other elements.

Electro Chemiluminiscent Assays

• ECL is a process in which highly reactive species are generated from stable precursors at the surface of electrode. These highly reactive species react with one another producing light.
• The development of ECL is based on ruthenium-tris complex and tripropylamine (TPA), the final chemiluminescence is formed during the detection step.
• The chemiluminescent reactions that lead to emission of light from the complex are initiated electrically, which is achieved by applying a voltage to the immunological complex.
• The application of voltage creates an electrical field, which causes all the material in the field to react.
• TPA oxidise to release an electron and forms an intermediatecation finally resulting in TPA radical.
• The ruthenium complex also releases an electron at the surface of the electrode to form rutheniumcation.
• This ruthenium cation and TPA radical reacts to form chemiluminescent.
• ECL signal generation occurs when voltage is applied to the detection cell electrode, a peak of light emission occurs over a short time interval and is detected as ECL signal.
  

The writer is Director-Technical Wellspring chain of laboratories
Email: npilphadkelab@vsnl.net