TFTs and Endocrinological Assessment
Introduction
TFTs or thyroid function tests, diagnostic criteria for diabetes mellitus, screening tests for all other endocrinological conditions, these are just some of the confusing puzzles that you need to solve to pass the exams.
If you could understand the physiology behind these tests, it would make your life a lot easier. If you could go a step further and narrow the diagnostic tests down to a small number that you need to remember, your life just gets wonderful!
Well, wait no more! The Hands-on Guide to Clinical Reasoning in Medicine will do just that. It has been written keeping its audience in mind in a friendly, easy-to understand, easy to use, practical, hands-on style for students, junior doctors and nurse practitioners.
Chapters take you through history taking, clinical examination in endocrinology, test interpretation and clinical presentations. You will not only gain knowledge but also learn decision-making that is tested in exams and on a daily basis.
For instance, did you know that Grave’s ophthalmopathy or pretibial myxedema does not automatically mean hyperthyroidism? In fact, one can still be euthyroid or even hypothyroid with Grave’s eye signs, since the physical features can persist despite treatment. Knowing that, the assessment of thyroid status is independent of the presentation like Grave’s ophthalmopathy, clears up a lot of confusion.
Topics covered include:
A novel and simple approach to history taking in endocrinology is illustrated. This is one specialty where the symptoms can cut across organ systems making it difficult to get your head around. Circumstances where you need to suspect an endocrinopathy are highlighted. This is followed by a single concept map showing the common symptom clusters that can occur in different endocrinopathies. Figure 1 shows this in action.
Figure 1
Credit source: Irfan M, Hands-on Guide to clinical Reasoning in Medicine, Wiley-Blackwell; 1 edition (1 Feb. 2019)
Using this knowledge, you will then be shown how to come up with the differentials, as you are collecting data, in a very practical way.
This is also illustrated in action in all the clinical presentations in a workbook format. You will have space to record your thoughts or just have a pause to think it through, as you solve the problems with the author.
Endocrinopathies need a holistic examination to decipher the bigger picture. This has been tackled in the book using the time-tested approach to examination starting with the hands, up the arms, face, down to the neck, torso and legs. All the signs of specific endocrinopathies are superimposed on an outline of the human body.
This is accompanied by text that focuses your mind on high yield factoids that commonly get asked in exams. These include:
- 5 differentials for a thyroid nodule – benign adenoma, toxic adenoma, thyroid carcinoma, single palpable nodule of multinodular goitre and thyroid cyst.
- Assessment of thyroid status that shows you how to establish if someone is euthyroid, hypo- or hyperthyroid.
- Skin bruising, hypertension and proximal myopathy are three features that are highly predictive of Cushing’s syndrome (Ross and Linch, 1982)
- Clinical examination in diabetes mellitus can be simplified by focussing on microvascular and macrovascular complications (see figure 2).
Ross, E. J. and Linch, D. C. (1982) ‘Cushing’s syndrome–killing disease: discriminatory value of signs and symptoms aiding early diagnosis.’, Lancet (London, England), 2(8299), pp. 646–9.
Figure 2
Credit source: Irfan M, Hands-on Guide to clinical Reasoning in Medicine, Wiley-Blackwell; 1 edition (1 Feb. 2019)
Most resources in endocrinology complicate the investigations by explaining innumerable convoluted tests. As a medical student, indeed as a general physician, we only need to understand the screening tests, leaving the more complicated stuff to the specialists.
Screening tests, in general, have high sensitivity. Therefore a true negative is followed by a more specific test which is done by the Endocrinologists. This again emphasises that clinical suspicion drives testing and not the test results!
The book does this by focussing on just the screening tests and explaining the physiology behind them. Understanding what they are testing, means that you don’t need to commit all of this to memory. See table 1 for a brief summary of all the screening tests in common endocrinopathies.
Table 1
Screening Tests in Endocrinology
| Endocrinopathy | Screening test | Physiology being tested |
|---|---|---|
|
Pituitary macroadenoma (>1 cm)
Pituitary microadenoma (<1 cm) – Most cost-effective test is prolactin. |
Thyrotroph (TSH, FT4)
Somatotroph (IGF-1) Lactotroph (prolactin) Gonadotroph (gonadotropins, TRH stimulated gonadotropins) Corticotroph (ACTH, 24 houre free urinary cortisol) |
Measure hypersecretion to identify cause
Measure hyposecretion to identify what needs replacing |
|
Prolactinoma |
Prolactin |
Levels distinguish between lactotroph micro and macroadenoma from stalk compression |
|
Acromegaly |
IGF-1 |
IGF-1 produced by the liver under the control of growth hormone |
|
Diabetes Insipidus |
Serum sodium, plasma and urine osmolality. |
Lack of ADH (craniogenic) or resistance to it (nephrogenic) causes dilute urine. |
|
Hyper and Hypothyroidism |
TSH |
FT4 only useful to discriminate primary from secondary and tertiary thyroid disorders |
|
Adequate thyroxine replacement in hypothyroidism |
TSH |
Adequate suppression means adequate replacement. |
|
Adequate treatment of hyperthyroidism |
FT3 and FT4 |
Because TSH remains suppressed for months in early treatment. |
|
Primary Hyperparathyroidism |
PTH |
Even a normal PTH with hypercalcemia is abnormal. |
|
Hypoparathyroidism |
PTH |
Low or normal with hypocalcemia |
|
Diabetes Mellitus |
Fasting plasma glucose
Post-prandial glucose
HbA1C
|
Each reflects different aspect of pathophysiology |
|
Cushing’s Syndrome |
Late night salivary cortisol
24 hour urinary free cortisol Low dose dexamethsaone suppression test |
Low pre-test probability needs a single screening test.
High pre-test probability needs two. |
|
Adrenal Insufficiency |
Short synacthen test |
Extrinsically stimulating the adrenal cortex to see if it produces cortisol |
|
Phaeochromocytoma |
24 hour urinary fractionated metanephrines and catecholamines |
Tumour metabolises catecholamines to produce these products. |
|
Primary Hyperaldosteronism or Conn’s Syndrome |
High Plasma Aldosterone/ Plasma Renin activity ratio
+ High Plasma Aldosterone |
Hyperaldosteronism causes sodium and water retention causing low renin levels. |
- Weight gain
- Palpitations
- Weight loss
- Thirsty and confused
Plenty of clinical scenarios will seamlessly integrate medical knowledge with the principles of decision-making, ensuring that you become a thinking clinician. These scenarios are played out in an engaging, conversational style with two imaginary students while the reader solves the problems with them.
Ready for a helping hand? You can find out all about Endocrinology right now and buy the Hands-on Guide to Clinical Reasoning in Medicine here.
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- Cardiology
- Pulmonolgy
- Neurology
- Gastroenterology
- Geriatric Medicine
- Nephrology
- Rheumatology
- Common Clinical Conditions
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