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← Endocrinology and metabolism indexChapter sections
Purpose and principlesIndications, selection and cautionsMethod and interpretationClinical next stepsRisks, monitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Approaching endocrine symptoms and hormone feedback loops

Endocrinology and metabolism · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

Shock with vomiting or hyperkalaemia, severe hypo- or hyperglycaemia with ketones or altered consciousness, profound sodium disturbance with seizure, severe calcium disturbance with arrhythmia, new visual loss with sudden headache, thyroid-related hyperthermia and delirium, or hypothermia with bradycardia requires immediate ABCDE care. Take useful endocrine samples when this causes no delay, but do not withhold hydrocortisone, glucose, fluids or other life-saving treatment while waiting for hormone results.

Purpose and principles

Convert non-specific symptoms into an anatomical endocrine hypothesis, interpret paired hormones through feedback physiology, and recognise results or presentations that need immediate treatment or specialist escalation.

Begin with phenotype and chronology rather than a broad hormone screen. Polyuria requires distinction between osmotic diuresis, excess fluid intake and impaired urinary concentration. Weight loss with heat intolerance, tremor and diarrhoea suggests thyrotoxicosis; weight loss with postural symptoms, nausea and hyperpigmentation suggests primary adrenal insufficiency; weight loss with thirst and nocturia suggests diabetes mellitus. Conversely, fatigue and weight gain occur in depression, sleep apnoea, anaemia, medication effects and endocrine disease. Document speed of onset, episodic versus sustained symptoms, pregnancy possibility, pubertal or menopausal context, family syndromes and previous head, neck, pituitary, adrenal or pancreatic treatment. Examine pulse, blood pressure including posture, body habitus, skin, visual fields, thyroid, proximal power, reflexes and hydration according to the hypothesis.

Indications, selection and cautions

Primary gland failure

A low target hormone with a clearly raised controlling hormone supports failure at the target gland, such as low free T4 with high TSH or low cortisol with high ACTH in the appropriate context.

Central endocrine failureRed flag

A low end hormone with a low or merely normal trophic hormone is discordant and can indicate hypothalamic or pituitary disease, particularly when several axes or visual symptoms coexist.

Autonomous hormone excess

A high target hormone with appropriate suppression of its controller suggests target-gland autonomy or exogenous hormone exposure; confirm medicines and assay validity before localisation imaging.

Pituitary mass effectRed flag

Progressive visual-field loss, diplopia, severe headache, ophthalmoplegia or multiple pituitary deficits needs urgent pituitary assessment; abrupt headache and visual change raises apoplexy.

Adrenal crisis phenotypeRed flag

Hypotension, vomiting, abdominal pain, fever, hyponatraemia, hyperkalaemia or hypoglycaemia in someone with steroid exposure or autoimmune disease justifies immediate hydrocortisone and resuscitation.

Assay or context discordance

Results incompatible with physiology, symptoms or each other suggest acute illness, wrong sampling time, biotin, drug interference, binding-protein change, macrohormone or analytical error rather than rare disease automatically.

Method and interpretation

  1. 01
    Paired TSH and free T4First step
    Why
    Assess the thyroid axis and distinguish primary thyroid dysfunction from a potentially central pattern.
    Interpretation and limitations
    High TSH with low free T4 supports primary hypothyroidism; suppressed TSH with high free hormone supports thyrotoxicosis. Low free T4 with non-raised TSH needs pituitary and illness review.
  2. 02
    8 am to 9 am cortisol with ACTH
    Why
    Screen suspected adrenal insufficiency at the physiologically informative time and help localise confirmed deficiency.
    Interpretation and limitations
    Apply NICE and the local assay thresholds. A low cortisol with raised ACTH supports primary failure; ACTH must be drawn before steroid when feasible, but crisis treatment must not wait.
  3. 03
    Albumin-adjusted calcium with PTH
    Why
    Determine whether confirmed calcium disturbance is parathyroid-mediated and identify dangerous severity.
    Interpretation and limitations
    PTH should be suppressed during hypercalcaemia; a raised or inappropriately normal value supports primary hyperparathyroidism. Correct magnesium, renal, vitamin D and medicine context before final attribution.
  4. 04
    Plasma glucose and capillary ketones
    Why
    Identify diabetes, hypoglycaemia and ketotic insulin deficiency during polyuria, weight loss or acute illness.
    Interpretation and limitations
    Ketonaemia with acidosis is DKA even when glucose is not strikingly high, particularly with SGLT2 exposure. Treat the acute state before refining diabetes type.

Clinical next steps

01First encounterBuild an axis hypothesisFirst stepNon-specific symptoms raise the possibility of endocrine disease.+
  1. 1Define tempo, episodic triggers, weight and fluid balance, reproductive symptoms, family syndromes and every prescribed, injected, inhaled, topical and non-prescription hormone-active product.
  2. 2Examine physiology and targeted signs, separating an acutely unstable presentation from a stable outpatient question before ordering broad tests.
  3. 3Choose the smallest set of paired hormones and safety bloods that can answer the proposed axis and important alternatives, documenting sampling conditions.
  4. 4Interpret results against pre-test probability and feedback physiology, then decide whether to repeat, dynamically test, image or refer rather than expanding indiscriminately.
02Discordant resultCheck context before rare diagnosesA hormone result conflicts with symptoms, its paired controller or previous measurements.

Risks, monitoring and follow-up

  • Record symptom trajectory and objective weight, pulse, postural blood pressure, fluid balance and menstrual or sexual function rather than relying on fatigue alone.
  • Maintain a results table pairing each target hormone with its controller, sampling time, acute illness and relevant medicines so axis patterns remain visible.
  • Track every abnormal result to repeat, dynamic test, referral or documented resolution, including laboratory advice when interference was suspected.
  • Escalate new vomiting, postural collapse, severe thirst, ketones, confusion, seizure, headache or visual change as a new risk state, not a routine clinic fluctuation.
  • After changing a hormone-active medicine, repeat testing only at the interval appropriate to that axis and formulation, avoiding premature dose cycling.

Special situations

Normal can be inappropriate

Reference ranges describe populations, not feedback adequacy. A normal TSH is abnormal if free T4 is low and the pituitary should be mounting a strong response.

Controller and product localise

Paired hormones turn an abnormal amount into an anatomical hypothesis. The same low end hormone has different implications when its trophic signal is high versus low.

Pulses defeat snapshots

Growth hormone and several reproductive hormones vary in pulses, so a random sample may reflect timing rather than disease. Integrated markers or dynamic tests answer better questions.

Drugs alter axes twice

Medicines may change true physiology and also interfere with measurement. Glucocorticoids suppress ACTH, while biotin can distort some immunoassays without changing the patient's hormone state.

Incidental lesions are common

Small pituitary, thyroid and adrenal lesions occur in people without hormone disease. Biochemical and clinical concordance prevents an image from hijacking the diagnosis.

Common pitfalls

  1. 01

    Ordering a wide endocrine panel without a phenotype, then constructing diagnoses around chance out-of-range values.

  2. 02

    Calling a trophic hormone normal without asking whether it is appropriate for the paired end hormone.

  3. 03

    Ignoring topical, inhaled, injected or over-the-counter glucocorticoid exposure during adrenal assessment.

  4. 04

    Requesting pituitary MRI before confirming a persistent biochemical axis abnormality in a stable patient.

  5. 05

    Repeating mildly discordant tests during the same acute illness and treating regression-to-the-mean as physiology.

  6. 06

    Waiting for cortisol or thyroid results before treating a clinically suspected adrenal or metabolic emergency.

Practice

Two practice questions

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Endocrinology and metabolismOriginal SBA

Localising low thyroid hormone

A patient with previous pituitary surgery has fatigue. Free T4 is below the laboratory range and TSH is mid-range normal. Which interpretation best applies feedback physiology?

Choose one answer, then submit
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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE NG145 thyroid diseasePaired thyroid testing, acute-illness cautions, biotin and repeat-testing principles.
  • NICE NG243 adrenal insufficiencyRecognition, morning cortisol testing, emergency treatment and referral.
  • Society for Endocrinology clinical guidanceUK endocrine emergency frameworks across adrenal, pituitary, sodium and calcium disorders.
  • NICE NG132 primary hyperparathyroidismRepeat calcium, PTH interpretation and specialist assessment.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
Negative feedback localises disease. The hypothalamus and pituitary stimulate a target gland, and the target hormone restrains upstream secretion. In primary hypothyroidism, low thyroid hormone releases restraint and TSH rises; in pituitary disease, low free T4 is accompanied by TSH that is low or insufficiently raised. Primary adrenal failure produces low cortisol with raised ACTH, while central failure has low or inappropriately normal ACTH, although treatment must precede this distinction in crisis. Primary hypogonadism tends to raise LH and FSH, while central hypogonadism does not. Autonomous thyroid hormone, cortisol or sex-steroid secretion often suppresses the controller. Prolactin is an important exception because tonic hypothalamic dopamine inhibits rather than stimulates secretion, so stalk disruption and dopamine-antagonist medicines raise prolactin.

Physiology also explains why one sample may mislead. Cortisol has a circadian rhythm and rises with acute stress; growth hormone is pulsatile, making a random concentration generally unhelpful; testosterone is time-sensitive; renin and aldosterone depend on posture, sodium, potassium and medicines. Pregnancy changes binding proteins and axis reference ranges. Severe non-thyroidal illness can lower TSH or thyroid hormones without primary thyroid disease. Immunoassays are vulnerable to biotin, heterophile antibodies and macrohormones. Frame every result as pre-test probability plus sample conditions plus paired-axis logic. Repeat a low-risk discordant result under controlled conditions, contact biochemistry when interference is plausible, use dynamic testing for the specific remaining question and image only when biochemical and structural questions align.

Key points

  • Endocrine symptoms such as fatigue, weight change, thirst, menstrual disturbance and palpitations are common; specificity comes from tempo, associated signs, medicines and a coherent physiological pattern.
  • Interpret a target-gland hormone with its controlling hormone whenever the axis permits: an isolated number often cannot distinguish primary gland disease from hypothalamic or pituitary disease.
  • In primary target-gland failure the end hormone is low and the trophic hormone usually rises; in central failure the trophic hormone is low or inappropriately normal for the low end hormone.
  • Autonomous end-hormone excess usually suppresses its upstream controller, whereas central trophic-hormone excess produces an unsuppressed or raised controller despite a high target hormone.
  • Time, posture, fasting, sleep, menstrual phase, pregnancy, acute illness and recent exercise can change a valid result without any gland being diseased.
  • Ask about every glucocorticoid route, biotin supplements, dopamine-active medicines, opioids, lithium, amiodarone and sex hormones before interpreting cortisol, thyroid, prolactin or gonadal axes.
  • An apparently normal controlling hormone may be pathological when the end hormone is abnormal: normal TSH with low free T4 can be inappropriately normal in central hypothyroidism.
  • 05
    Serum and urine osmolality with sodium
    Why
    Classify polyuria or dysnatraemia by relating circulating tonicity to renal water handling.
    Interpretation and limitations
    In hypernatraemia, inappropriately dilute urine suggests impaired vasopressin action; in hyponatraemia, interpretation requires volume, glucose, cortisol, thyroid, diuretic and urine-sodium context.
  • 06
    Prolactin with pregnancy, thyroid and medicine review
    Why
    Evaluate galactorrhoea, hypogonadism or pituitary symptoms while excluding common physiological and pharmacological causes.
    Interpretation and limitations
    Repeat a mild stress-associated rise under calm conditions and ask the laboratory about macroprolactin. Marked persistent elevation or mass-effect symptoms warrants endocrine imaging review.
    • +
    1. 1Verify identity, units, time, fasting or posture requirements and whether acute illness, pregnancy or recent exercise altered physiology.
    2. 2AlternativeReview biotin, glucocorticoids, dopamine agents, opioids, lithium, amiodarone and sex hormones, and ask biochemistry about assay interference or alternative methodology.
    3. 3EscalationRepeat at an appropriate interval under standardised conditions when the abnormality is mild and clinically safe, retaining urgent escalation for dangerous values or symptoms.
    4. 4Use specialist dynamic testing or imaging only after the residual physiological question is explicit and the result would change management.
    03Emergency axisTreat physiology before localisationShock, seizure, altered consciousness, severe electrolyte disturbance or visual catastrophe suggests endocrine crisis.+
    1. 1Start ABCDE care, bedside glucose and ketones, ECG, venous access and urgent renal, electrolyte, osmolality and acid-base assessment while summoning senior help.
    2. 2Draw cortisol, ACTH or other time-critical specimens if immediately available, but give hydrocortisone, glucose, fluid or calcium treatment without diagnostic delay when indicated.
    3. 3Engage endocrinology and the relevant acute specialty, including neurosurgery or ophthalmology for pituitary mass effect and critical care for organ failure.
    4. 4After stabilisation, reconstruct pre-treatment samples, precipitant, medication omissions and axis location, then create prevention and follow-up plans.
    Confirm biochemical disease before searching for a small pituitary or adrenal lesion, except when acute mass effect, apoplexy, cancer or another structural emergency drives imaging first.
  • Interpret results with the laboratory's current assay, reference interval, sampling protocol and endocrine advice because reference ranges and dynamic decision limits are method-specific.