Glomerular Disease Subspecialty · KIMS Secunderabad
Sarcoidosis and the Kidneys — How Granulomas Damage Kidney Function
Sarcoidosis is a multisystem granulomatous disease of unknown aetiology — characterised by the formation of non-caseating (no central necrosis — distinguishing it from tuberculosis) granulomas in affected organs. The lungs, lymph nodes, skin, and eyes are the most commonly affected organs, but the kidneys are involved in a clinically significant proportion of patients. Kidney involvement in sarcoidosis occurs through two distinct mechanisms: direct granulomatous infiltration of the renal interstitium (granulomatous tubulointerstitial nephritis — GTIN), and hypercalcaemia-mediated kidney injury from the increased 1,25-OH vitamin D production by sarcoid granulomas.
Renal involvement in sarcoidosis is clinically important because it is treatable — steroids suppress granuloma formation and lower 1,25-OH vitamin D production, normalising calcium and protecting kidney function — but it must be identified before significant fibrosis has occurred. In India, sarcoidosis may be underdiagnosed because its pulmonary and lymph node involvement is frequently misdiagnosed as tuberculosis (both cause bilateral hilar lymphadenopathy and pulmonary infiltrates). Distinguishing sarcoidosis from TB is essential because steroids — the treatment for sarcoidosis — worsen active TB.
Two mechanisms of kidney damage in sarcoidosis
1. Granulomatous tubulointerstitial nephritis (GTIN) — direct kidney infiltration
Sarcoid granulomas form in the renal interstitium, surrounding and compressing tubules and reducing their function. The granulomas are non-caseating on biopsy — this is the crucial histological distinction from renal tuberculosis (which shows caseating granulomas) and from foreign body granulomas. GTIN presents as declining eGFR, mild proteinuria, and sometimes haematuria. The kidney is often enlarged on imaging (from granulomatous infiltration). Kidney biopsy is required for diagnosis — non-caseating granulomas with multinucleate Langerhans-type giant cells are pathognomonic.
2. Hypercalcaemia and hypercalciuria — calcium-mediated kidney injury
Sarcoid granulomas contain activated macrophages that express 1-alpha hydroxylase — the same enzyme normally found only in the kidney. This results in excessive conversion of 25-OH vitamin D to active 1,25-OH vitamin D (calcitriol) — independent of the normal PTH-regulated kidney pathway. The excess calcitriol increases intestinal calcium absorption and bone calcium mobilisation, causing hypercalcaemia and hypercalciuria. The consequences for the kidney: nephrocalcinosis (calcium deposits in the medullary tubules), calcium nephropathy (direct tubular toxicity from hypercalcaemia), and — if untreated — CKD. Serum calcium, 1,25-OH vitamin D, and ACE level are elevated; PTH is suppressed (secondary to the hypercalcaemia).
Clinical features
Elevated creatinine and eGFR decline — from GTIN, nephrocalcinosis, or both.
Hypercalcaemia symptoms — polyuria (from nephrogenic diabetes insipidus caused by hypercalcaemia), polydipsia, nausea, constipation, lethargy, and bone pain.
Nephrolithiasis — hypercalciuria promotes calcium oxalate and calcium phosphate stone formation.
Proteinuria — usually mild (below 1 g/day) in GTIN; occasionally nephrotic range if glomerular involvement is present.
Systemic sarcoidosis features — bilateral hilar lymphadenopathy (on chest X-ray), pulmonary infiltrates, erythema nodosum (tender red nodules on the shins), uveitis, skin plaques, and facial nerve palsy (neurosarcoidosis).
Diagnosis at KIMS
| Investigation | What it identifies |
|---|---|
| Serum calcium and 24-hour urine calcium | Hypercalcaemia and hypercalciuria from excess 1,25-OH vitamin D production by sarcoid granulomas |
| 1,25-OH vitamin D (calcitriol) | Elevated — the mechanism of hypercalcaemia in sarcoidosis (granulomas activate 25-OH vitamin D) |
| PTH (intact) | Suppressed — secondary to hypercalcaemia (distinguishes from primary hyperparathyroidism where PTH is elevated) |
| ACE (angiotensin-converting enzyme) level | Elevated in approximately 60% of active sarcoidosis — secreted by sarcoid granuloma macrophages. Not specific but useful corroborating evidence |
| Chest X-ray and CT chest | Bilateral hilar lymphadenopathy and/or pulmonary infiltrates — the most common finding in sarcoidosis |
| Kidney biopsy with LM and IF at KIMS | Non-caseating granulomas with Langerhans giant cells — pathognomonic of sarcoidosis. Distinguishes from TB (caseating), IgG4 (storiform fibrosis + IgG4 plasma cells), and drug-induced TIN |
| TB exclusion (Mantoux, CBNAAT, AFB culture) | Essential before starting steroids — sarcoidosis and TB can both cause bilateral hilar lymphadenopathy and granulomatous nephritis. Steroids given to a patient with active TB are life-threatening |
Treatment
Prednisolone — the primary treatment
0.5 to 1.0 mg/kg/day initially, tapered over 6 to 12 months. Steroids suppress granuloma formation, reducing ACE production, normalising 1,25-OH vitamin D, and lowering serum calcium. eGFR often improves substantially within 4 to 8 weeks — distinguishing sarcoid GTIN (steroid-responsive) from fibrotic TIN (which does not respond). The established fibrotic scar from untreated GTIN does not reverse — early treatment preserves more kidney function.
Hydroxychloroquine — for hypercalcaemia management
Inhibits the 1-alpha hydroxylase enzyme in granulomas, reducing 1,25-OH vitamin D production and calcium levels. Useful as a steroid-sparing agent for hypercalcaemia-predominant disease or for long-term calcium management in chronic sarcoidosis.
Hydration and dietary calcium moderation
High fluid intake dilutes urinary calcium, reducing nephrolithiasis and nephrocalcinosis risk. Dietary calcium restriction is not usually required — but avoiding vitamin D supplementation (which worsens the already-elevated 1,25-OH vitamin D-driven hypercalcaemia) is important.
Book a Nephrology Consultation for Sarcoidosis Kidney Disease at KIMS
Frequently Asked Questions — Sarcoidosis and Kidney Disease
Clinically significant kidney involvement — with elevated creatinine, hypercalcaemia, or nephrolithiasis — occurs in approximately 5 to 10% of patients with systemic sarcoidosis. Subclinical involvement (detectable only by kidney biopsy in patients with no kidney symptoms) may be higher. Hypercalciuria (elevated urine calcium without hypercalcaemia) occurs in 40 to 50% of sarcoidosis patients and is the most common renal manifestation. Kidney stones from hypercalciuria affect approximately 10 to 15% of sarcoidosis patients. Granulomatous tubulointerstitial nephritis — the most serious renal complication — is less common but clinically important because of its treatability and progressive nature if untreated.
Sarcoidosis causes hypercalcaemia through an unusual mechanism — the granulomas themselves produce the activated form of vitamin D (1,25-OH vitamin D, calcitriol) via the 1-alpha hydroxylase enzyme normally restricted to the kidney. This granuloma-produced calcitriol is not regulated by the normal PTH feedback mechanism — it continues to be produced regardless of blood calcium levels. The excess calcitriol increases intestinal calcium absorption and bone calcium release, raising blood and urinary calcium. The elevated calcium suppresses PTH (the body's attempt to lower calcium through its normal regulatory channel). This is why sarcoidosis hypercalcaemia shows the pattern: elevated calcium + suppressed PTH + elevated 1,25-OH vitamin D — distinguishing it from primary hyperparathyroidism (elevated calcium + elevated PTH) and vitamin D toxicity (elevated 25-OH vitamin D rather than 1,25-OH).
Both TB and sarcoidosis cause granulomatous interstitial nephritis — the kidney biopsy appears superficially similar. The critical distinction is on light microscopy: TB granulomas are caseating (showing central necrosis — the cheese-like dead tissue at the core of the granuloma) while sarcoidosis granulomas are non-caseating (no central necrosis, just compact epithelioid cells and giant cells). AFB staining of the biopsy tissue may show acid-fast bacilli in TB but will be negative in sarcoidosis. Additional tests: AFB culture of urine (positive in renal TB, negative in sarcoidosis), CBNAAT on urine (MTB detection), and the clinical response to steroids (sarcoidosis responds; TB worsens or develops complications).
Prednisolone causes hyperglycaemia — often worsening pre-existing diabetes or precipitating new steroid-induced diabetes. This must be managed carefully, with more frequent glucose monitoring, intensification of antidiabetic therapy during steroid treatment, and a higher threshold for insulin use. In diabetic patients with sarcoidosis kidney disease, the KIMS nephrology team manages both the steroid treatment and the diabetes-steroid interaction simultaneously. The risks of untreated progressive sarcoid GTIN generally outweigh the risks of steroid-induced glucose management in the medium term — but the metabolic risks must be explicitly managed rather than ignored.
KIMS Secunderabad — Dr. Aswini Dutt T (glomerular disease subspecialty), kidney biopsy with NABL LM + IF + EM and non-caseating granuloma confirmation, 1,25-OH vitamin D, ACE level, serum and urine calcium, TB exclusion (CBNAAT, AFB culture) before steroids, prednisolone treatment with hydroxychloroquine for hypercalcaemia, long-term eGFR and calcium monitoring. NABH and NABL accredited. Call 040-4488-5000.