Hypertension, or high blood pressure, is one of the most prevalent chronic diseases globally. It increases the risk of cardiovascular diseases, stroke, kidney failure, and premature death. While primary (essential) hypertension accounts for 90–95% of cases, the remaining 5–10% are classified as secondary hypertension—high blood pressure caused by an underlying, identifiable condition.
Timely diagnosis and management of secondary hypertension are crucial because treating the root cause can cure or significantly improve the patient’s condition.
To help remember the causes of secondary hypertension, medical professionals use the mnemonic RENALS, each letter standing for a category of conditions.
Overview of the RENALS Mnemonic
The RENALS mnemonic stands for:
- R: Renal causes
- E: Endocrine causes
- N: Neurogenic causes
- A: Aortic coarctation
- L: Little people (Pregnancy-related hypertension)
- S: Stress-related hypertension
This framework aids clinicians, students, and healthcare providers in conducting a thorough differential diagnosis of elevated blood pressure.
R – Renal Causes of Hypertension
Key Conditions:
- Glomerulonephritis
- Renal Artery Stenosis (RAS)
- Polycystic Kidney Disease
- Chronic Kidney Disease (CKD)
- Renin-secreting tumors
Mechanism:
The kidneys regulate blood pressure through the renin-angiotensin-aldosterone system (RAAS). When renal perfusion drops (due to stenosis, inflammation, or obstruction), renin secretion increases, leading to vasoconstriction and sodium retention.
Clinical Signs:
- Elevated serum creatinine
- Proteinuria
- Flank pain (in polycystic kidney disease)
- Abdominal bruit (in RAS)
Diagnosis:
- Doppler ultrasound
- Renal angiography
- Serum BUN and creatinine
- Urinalysis
Treatment:
- ACE inhibitors or ARBs
- Surgical intervention (e.g., stenting for RAS)
- Immunosuppressants (in glomerulonephritis)
E – Endocrine Causes
Major Endocrine Conditions:
- Cushing’s syndrome
- Conn’s syndrome (primary hyperaldosteronism)
- Pheochromocytoma
- Thyroid disorders (hyperthyroidism, hypothyroidism)
- Oral contraceptive pills (OCPs)
Mechanism:
Endocrine disorders alter hormonal regulation of vascular tone and volume:
- Cushing’s: Excess cortisol increases BP via sodium retention
- Conn’s: Aldosterone excess leads to hypokalemia and hypertension
- Pheochromocytoma: Episodic catecholamine release causes paroxysmal hypertension
- OCPs: Estrogens promote fluid retention
Diagnosis:
- 24-hour urinary cortisol or dexamethasone suppression test (Cushing’s)
- Serum aldosterone/renin ratio (Conn’s)
- Plasma metanephrines (Pheochromocytoma)
- Thyroid profile (TSH, T3, T4)
Treatment:
- Surgical removal of adrenal tumors
- Hormone replacement or suppression therapy
- Discontinuation of OCPs
N – Neurogenic Causes
Common Neurological Conditions:
- Raised Intracranial Pressure (ICP)
- Brainstem lesions
- Autonomic dysreflexia (in spinal cord injuries)
- Neuroblastoma (in children)
Mechanism:
The brainstem regulates sympathetic output. Any increase in intracranial pressure or autonomic dysfunction can lead to:
- Increased sympathetic tone
- Systemic vasoconstriction
- Elevated BP
Cushing's triad (a classic sign of raised ICP):
- Hypertension
- Bradycardia
- Irregular respirations
Diagnosis:
- CT/MRI of the brain
- Fundoscopy (for papilledema)
- Neurological examination
Treatment:
- Osmotic diuretics (e.g., mannitol)
- Corticosteroids (for cerebral edema)
- Neurosurgical decompression
A – Aortic Coarctation
What Is It?
A congenital narrowing of the aorta, usually near the ductus arteriosus, leading to elevated blood pressure in the upper limbs and reduced pressure in the lower limbs.
Clinical Signs:
- Hypertension in arms, hypotension in legs
- Weak or delayed femoral pulses
- Rib notching on chest X-ray
- Murmur between scapulae
Diagnosis:
- Echocardiography
- CT angiography or MRI
- Blood pressure comparison between limbs
Treatment:
- Surgical correction
- Balloon angioplasty
- Lifelong monitoring for re-narrowing or aneurysms
L – Little People: Pregnancy-Induced Hypertension (PIH)
Types:
- Gestational hypertension (BP >140/90 after 20 weeks, no proteinuria)
- Preeclampsia (hypertension + proteinuria ± systemic involvement)
- Eclampsia (preeclampsia + seizures)
Risk Factors:
- First pregnancy
- Multiple gestation
- Pre-existing diabetes or renal disease
- Obesity
Pathophysiology:
Poor placental perfusion → systemic endothelial dysfunction → vasospasm, increased vascular resistance, and volume overload
Diagnosis:
- BP monitoring
- Proteinuria (dipstick or 24-hour urine)
- Liver enzymes, platelets, creatinine
Treatment:
- Antihypertensives (labetalol, methyldopa)
- Magnesium sulfate (for seizure prophylaxis)
- Timely delivery
S – Stress and Other Situational Causes
Categories:
- Trauma (e.g., post-operative or pain-related hypertension)
- White Coat Hypertension (elevated BP in clinical settings)
- Psychological Stress or Anxiety Disorders
- Post-Traumatic Stress Disorder (PTSD)
Mechanism:
Stress stimulates the sympathetic nervous system, leading to:
- Increased heart rate
- Vasoconstriction
- Temporary or sustained rise in BP
Diagnosis:
- Ambulatory BP monitoring
- Stress tests
- Psychiatric assessment (if needed)
Treatment:
- Behavioral therapy
- Anxiolytics (in selected cases)
- Lifestyle interventions
Table: Summary of RENALS Mnemonic for Hypertension
| Letter | Category | Example Conditions | Diagnostic Tools |
|---|---|---|---|
| R | Renal | Glomerulonephritis, Renal artery stenosis | Renal Doppler, creatinine, urinalysis |
| E | Endocrine | Cushing's, Conn's, Pheochromocytoma, OCPs | Hormonal assays, imaging, suppression tests |
| N | Neurogenic | Raised ICP, brainstem lesion, dysreflexia | CT/MRI, fundoscopy |
| A | Aortic | Aortic coarctation | Echocardiogram, BP comparison |
| L | Pregnancy | Gestational HTN, preeclampsia, eclampsia | Urine protein, fetal monitoring |
| S | Stress | Trauma, white coat, PTSD | Ambulatory BP, psychological evaluation |
Frequently Asked Questions (FAQs)
Q1. What is secondary hypertension?
Secondary hypertension is high blood pressure caused by an identifiable medical condition like kidney disease, hormonal imbalances, or structural anomalies.
Q2. Why is it important to identify secondary hypertension?
Because treating the underlying cause can often cure or dramatically improve blood pressure control.
Q3. How is secondary hypertension diagnosed?
Through targeted lab tests and imaging based on symptoms, age of onset, and resistance to treatment.
Q4. What is the most common cause of secondary hypertension in young adults?
Renal artery stenosis and coarctation of the aorta are common in younger individuals.
Q5. Can white coat hypertension be dangerous?
While often benign, it can indicate future risk of sustained hypertension and should be monitored.
