hplc

[SarCaustic]

What is HPLC (high performance liquid chromotography) used to detect in hospitals and why? I know that it is used to detect glycosylated haemoglobin, but I can't remember what such a detection indicates. Which other substances does it detect and what can their levels indicate?

[spat]

http://en.wikipedia.org/wiki/HPLC

[theprof]

HPLC is used in a a very wide range of tests in hospitals: I could type here all day long and not cover half of them. All the same, as a start how about:

Sickle cell screening
Identification and separation of metal binding proteins in human tissues
Distinguishing forms of haemoglobin in the circulation
Drug plasma level analysis
Monitoring by blood by-products during drug trials
Detection of heavy-metals in plasma from A+ E blood samples
Cellular phosphatase analysis in oncology
Preparatory steps in Edman Sequencing
Drug stability testing in shelf-life analysis to confirm manufacturers data.

HPLC equipment can vary considerably in sophistication. At the university where I work, I understand we have one of the most expensive and sophisticated models in the UK in the Chemistry Department . The problem is that due to budgetary constraints, UK hospital trusts often cannot afford the most advanced equipment. So at the end of the day, the equipment is only used to the limit of its capability in each hospital.

We've had two new HPLC state-of-the-art machines installed in my biochemistry department last month but in general, universities with medical schools and world-famous teaching hospitals are usually the better equipped.

[theprof]

Glycosylated haemoglobin is formed when the glucose in the bloodstream attaches itself to haemoglobin via a specific non-enzymatic process. Glycosylated haemoglobin is known as haemoglobin A1C or HbA1C. The higher the level of glucose in the blood, the greater the amount of HbA1C in the blood.

Now erythrocytes (red blood cells) normally live for somewhere between eight to twelve weeks before new cells replace them. Measuring the HbA1C in the blood will therefore provide an average blood glucose level over that eight to twelve week period.

As you should have realised by now, the HbA1C test is of immense value in the detection and treatment of diabetes. In a normal patient, the HbA1C is around 3.5% to 5.5%. An acceptable diabetic level usually ranges between about 4% to 6% for control via diet but anything above 6.5% calls for drug therapy, usually insulin. The test is also used to determine that drug therapy is controlling the diabetes within acceptable parameters every few months.

Different laboratories provide different types of assay in HbA1C tests. Some measure HbA1C produced by the glycolisation of the N-terminal valine of the B-chain of the haemoglobin whereas others measure the total glycosylated haemoglobin. The usual reason for these different assay methods is down to equipment costs. Because of this, there can be some variation in the assay results but its usually of no great significance.

It should be noted that HbA1C result figures are not the same as blood glucose level figures.

[theprof]

As far as your final question is concerned, it would be better if you asked "which substances does it not detect". HPLC is that good if the right analytical procedures are followed.

The results of HPLC assays are usually printed along side the average HPLC assay values in the human body. The physician then uses his clinical judgement based on that data to assess the health of the patient, the presence of disease etc.

[theprof]

That Wikipedia article cited by spat is quite a bit out of date. I haven't seen equipment like that shown in the photograph for years.