What are night sweats?
Night sweats are episodes of drenching perspiration severe enough to soak nightclothes and bedding — distinct from simply feeling warm or sweating a little. Occasional mild sweating at night is normal. True pathological night sweats are recurrent, drenching and disruptive, and may be accompanied by other symptoms such as fever, weight loss or lymph node swelling. The cause ranges from completely benign (room too hot, too many blankets) to conditions requiring urgent treatment.
Blood tests ordered for night sweats
| Test | What it checks for |
|---|---|
| CBC with differential | Lymphoma / leukaemia (abnormal white cells); anaemia; infection |
| ESR and CRP | Active inflammation — infection, autoimmune, malignancy |
| LDH | Very high in lymphoma — tumour burden marker |
| TSH (thyroid) | Hyperthyroidism — common cause of night sweats |
| Fasting glucose / HbA1c | Nocturnal hypoglycaemia in diabetes |
| HIV test | HIV causes night sweats, especially early infection and AIDS |
| Tuberculosis (TB) test — IGRA or Mantoux | TB is a classic cause of night sweats (B symptom) |
| Hormones (oestrogen / FSH in women; testosterone in men) | Menopause; male hypogonadism |
| Blood cultures (if febrile) | Bacterial endocarditis, bacteraemia |
Common causes of night sweats
Menopause and perimenopause
The most common cause of night sweats in women aged 45-55. Hot flushes and night sweats result from oestrogen withdrawal acting on the hypothalamic thermostat. FSH is elevated (confirming menopausal status). Hormone replacement therapy (HRT) is highly effective. Non-hormonal options include SSRIs, SNRIs and clonidine.
Hyperthyroidism
An overactive thyroid raises metabolic rate, causing heat intolerance, sweating (day and night), weight loss, palpitations and anxiety. TSH is suppressed (very low). Free T4 elevated. Treat with antithyroid medications or radioactive iodine.
Lymphoma (Hodgkin and Non-Hodgkin)
Night sweats are one of the 'B symptoms' of lymphoma (along with fever >38°C and unexplained weight loss >10% over 6 months). Drenching night sweats in someone with painless lymph node swelling, fatigue and weight loss should raise suspicion. CBC may show abnormal lymphocytes; LDH is often elevated. CT scan and lymph node biopsy are required for diagnosis.
Infections — TB, HIV, endocarditis
Tuberculosis classically causes night sweats, low-grade fever, cough and weight loss. HIV infection (primary and AIDS) causes night sweats. Bacterial endocarditis (heart valve infection) causes fever, night sweats, a heart murmur and embolic phenomena. All require specific testing.
Diabetes — nocturnal hypoglycaemia
Patients on insulin or sulfonylureas may develop low blood sugar at night, causing profuse sweating, nightmares and waking with palpitations. Fasting glucose and HbA1c may not detect this — a continuous glucose monitor or checking blood glucose when symptoms occur is needed.
Medications
Night sweats are a common side effect of: antidepressants (SSRIs, SNRIs — very common), tamoxifen, GnRH analogues, corticosteroids, some blood pressure medications and opioids.
Questions to ask your doctor
- Do I need to rule out lymphoma with a CT scan?
- Should I check TSH to rule out hyperthyroidism?
- Are my night sweats related to menopause?
- Could a medication be causing this?
- Should I have an HIV test and TB screening?