Thyroid Function Test (TFT) Explained: Normal Range, TSH, T3, T4, High & Low Levels (India 2026) | थायरॉइड फंक्शन टेस्ट गाइड
Thyroid Blood Test Explained: Normal Range, TSH, T3 & T4 — India 2026
थायराइड ब्लड टेस्ट: TSH, T3, T4 नॉर्मल रेंज, हाइपो vs हाइपर थायरायड की पूरी जानकारी
Thyroid blood tests are among the most commonly prescribed tests in India — ordered for everything from unexplained weight gain and fatigue to hair fall, pregnancy monitoring, and annual health checkups. Yet looking at TSH, T3, and T4 on a lab report is confusing for most patients. Why does a HIGH TSH mean the thyroid is underactive? What is the difference between T3 and T4? What does "subclinical hypothyroidism" mean?
This guide explains how to read a thyroid blood test report in India, in simple English and Hindi. If you are new to reading lab reports in general, start with our beginner's guide to blood test reports.
भारत में थायराइड टेस्ट सबसे आम टेस्टों में से एक है। यह गाइड TSH, T3 और T4 को सरल अंग्रेजी और हिंदी में समझाती है — नॉर्मल रेंज, हाइपो vs हाइपर, और रिपोर्ट कैसे पढ़ें।👁 Table of Contents / विषय सूची
The TSH Paradox — Why High TSH = Underactive Thyroid
The single most confusing aspect of thyroid reports for Indian patients is this: a High TSH means the thyroid is underactive (hypothyroid), and a Low TSH means the thyroid is overactive (hyperthyroid). This seems backwards — until you understand how the brain-thyroid system works.
थायराइड रिपोर्ट के बारे में सबसे भ्रामक पहलू: उच्च TSH = थायराइड कम सक्रिय (हाइपोथायरायड) और कम TSH = थायराइड अधिक सक्रिय (हाइपरथायरायड)। यह उल्टा लगता है — जब तक आप मस्तिष्क-थायराइड प्रणाली को नहीं समझते।Normal Range in India / भारत में सामान्य सीमा
*Ranges vary between labs. The Free T3/T4 ranges are different from Total T3/T4 — check which your report measures. In pregnancy, the TSH upper limit drops significantly. Always use the reference range printed on your specific report.
*लैब के बीच सीमाएं भिन्न होती हैं। Free T3/T4 की सीमाएं Total T3/T4 से अलग हैं। गर्भावस्था में TSH की ऊपरी सीमा काफी कम हो जाती है।| Test / टेस्ट | Normal Range (Adult) | Unit | What it represents |
|---|---|---|---|
| TSH थायराइड स्टिमुलेटिंग हार्मोन |
0.4 – 4.0 | mIU/L | Primary screening test. Brain signal to thyroid. High = underactive; Low = overactive. |
| Total T3 ट्राईआयोडोथायरोनिन |
80 – 200 | ng/dL | The active thyroid hormone. Controls metabolism, heart rate, temperature. |
| Free T3 (FT3) | 2.3 – 4.2 | pg/mL | The unbound active fraction — more clinically useful than Total T3. |
| Total T4 थायरोक्सिन |
5.0 – 12.0 | µg/dL | Storage hormone made by thyroid. Converted to active T3 in tissues. |
| Free T4 (FT4) | 0.7 – 1.8 | ng/dL | Unbound T4 — most commonly ordered alongside TSH in Indian labs. |
| TSH in Pregnancy गर्भावस्था में TSH |
1st tri: < 2.5 · 2nd–3rd tri: < 3.0 | mIU/L | Significantly tighter range in pregnancy — even mild thyroid dysfunction affects foetal brain development. |
Hypothyroidism vs Hyperthyroidism / हाइपो vs हाइपर
Pattern: High TSH + Low T3/T4. The thyroid is not making enough hormone. Most common in India — particularly in women above 30, and during or after pregnancy. The most common cause in India is Hashimoto's thyroiditis (autoimmune), detected by elevated Anti-TPO antibodies. Symptoms: weight gain, fatigue, cold intolerance, hair fall, constipation, dry skin, depression, slow heart rate, heavy periods.
Pattern: Low TSH + High T3/T4. The thyroid is producing too much hormone — accelerating all body functions. Most common cause in India: Graves' disease (autoimmune), multinodular goitre, or thyroiditis. Symptoms: unexplained weight loss, palpitations (fast heart rate), excessive sweating, heat intolerance, tremor, anxiety, diarrhoea, light or missed periods. Requires urgent treatment — untreated hyperthyroidism can cause cardiac arrhythmias.
| Condition / स्थिति | TSH | T3 / T4 | Common symptoms in India |
|---|---|---|---|
| Normal | 0.4–4.0 | Normal | No symptoms from thyroid |
| Hypothyroidism हाइपोथायरायडिज्म |
High (> 4.0) | Low | Weight gain, fatigue, hair fall, cold intolerance, constipation, slow pulse, heavy periods |
| Hyperthyroidism हाइपरथायरायडिज्म |
Low (< 0.4) | High | Weight loss, palpitations, tremor, anxiety, heat intolerance, frequent stools, light periods |
| Subclinical Hypothyroidism | Mildly high (4–10) | Normal | Mild or no symptoms — grey zone requiring clinical judgement |
| Subclinical Hyperthyroidism | Mildly low (< 0.4) | Normal | Often asymptomatic — important to monitor; risk of atrial fibrillation in elderly |
Subclinical Thyroid — The Grey Zone / सब-क्लिनिकल थायरायड
Subclinical thyroid conditions are extremely common in India — often discovered on routine checkups in patients with no obvious symptoms. Understanding them prevents unnecessary anxiety and unnecessary treatment.
भारत में सब-क्लिनिकल थायरायड स्थितियां बेहद आम हैं — अक्सर नियमित जांच पर बिना किसी स्पष्ट लक्षण के मरीजों में पाई जाती हैं।TSH mildly elevated (4–10 mIU/L) with normal Free T4. The most common thyroid finding on routine Indian health checkups. Whether to treat depends on: degree of TSH elevation, symptoms, age, pregnancy status, and Anti-TPO antibody status. TSH above 10 is usually treated regardless. TSH 4–10 in a pregnant woman — always treat. TSH 4–10 in a young woman trying to conceive — discuss treatment with doctor. Retesting in 3–6 months before starting treatment is often reasonable in mild cases.
TSH suppressed below 0.4 mIU/L with normal T3/T4. Common causes in India: excess thyroid medication (over-replacement), early Graves' disease, and thyroid nodules. Important to investigate because even mild TSH suppression increases the risk of atrial fibrillation (irregular heartbeat) in patients above 60 and accelerates bone loss. Requires calcium and bone density monitoring in older patients.
Related Tests Doctors Often Order / संबंधित टेस्ट
Thyroid abnormalities rarely exist in isolation. Doctors typically order these tests alongside or after an abnormal thyroid panel to find the cause and assess consequences:
थायराइड असामान्यताएं शायद ही कभी अकेले होती हैं। कारण खोजने और परिणामों का आकलन करने के लिए डॉक्टर आमतौर पर ये टेस्ट एक साथ या बाद में करवाते हैं:Anti-Thyroid Peroxidase (Anti-TPO) antibodies confirm whether hypothyroidism is autoimmune (Hashimoto's thyroiditis) — the most common cause in India. Elevated Anti-TPO means the immune system is attacking the thyroid. This changes the long-term management and also has implications for fertility and pregnancy. Always check Anti-TPO when TSH is persistently elevated. See our complete Anti-TPO guide.
Thyroid problems often coexist with Vitamin D deficiency and Vitamin B12 deficiency — all three cause overlapping symptoms (fatigue, hair fall, weakness, depression). A positive result for one should prompt checking the others. Vitamin D deficiency is found in 70–80% of Indians and worsens thyroid autoimmunity. B12 deficiency is especially common in vegetarians.
Hypothyroidism directly raises LDL cholesterol — sometimes dramatically. Patients with unexplained elevated cholesterol on a lipid profile should always have TSH checked. Treating hypothyroidism often normalises cholesterol without any cholesterol medication.
Both hypothyroidism and hyperthyroidism can cause anaemia — hypothyroidism by reducing red cell production, hyperthyroidism by increasing red cell breakdown. A CBC (Complete Blood Count) is essential when persistent fatigue, breathlessness, or pallor accompanies thyroid symptoms.
Thyroid dysfunction and diabetes have a bidirectional relationship — hypothyroidism worsens insulin resistance and blood sugar control, while diabetes patients have higher thyroid disorder rates. A HbA1c test is routinely checked alongside thyroid in any Indian patient with metabolic symptoms.
Hypothyroidism raises prolactin levels — causing irregular periods, absent periods, or infertility. In any woman with menstrual irregularity or difficulty conceiving, TSH and prolactin should be checked together. See our guide on female hormone tests.
Test Preparation / टेस्ट की तैयारी
-
The Medication Rule — most important for thyroid patients
If you take thyroid medication (Thyronorm, Eltroxin, Thyrox, or any levothyroxine brand), give your blood sample BEFORE taking your morning pill. Taking the medicine first will transiently suppress TSH and lower T4, making results appear falsely improved. After the blood draw, take your medicine as usual. Do not skip the morning dose — just delay it by 30–60 minutes until after the draw.
यदि आप थायराइड दवा (थायरोनॉर्म, एल्ट्रोक्सिन, थायरॉक्स) लेते हैं, तो ब्लड सैंपल देने के बाद अपनी सुबह की दवा लें। दवा पहले लेने से TSH दब जाएगा और T4 कम दिखेगा। -
The Biotin Warning — stop 48 hours before
Biotin (Vitamin B7) — widely taken in India for hair fall — causes significant interference in thyroid immunoassay tests. High-dose biotin (above 5 mg/day, common in "hair-skin-nail" supplements) can falsely lower TSH and falsely elevate T3/T4, mimicking hyperthyroidism. As confirmed by NCBI research, stop biotin supplements at least 48 hours before your thyroid test.
बायोटिन (विटामिन B7) — भारत में बालों के झड़ने के लिए व्यापक रूप से लिया जाता है — थायराइड परीक्षण में महत्वपूर्ण हस्तक्षेप करता है। थायराइड टेस्ट से कम से कम 48 घंटे पहले बायोटिन सप्लीमेंट बंद करें। -
Fasting NOT required — but morning is preferred
No fasting is required for TSH, T3, or T4. However, morning tests (7–10 AM) are preferred because TSH has a mild diurnal variation — it is slightly higher in the early morning and lower in the evening. For consistent serial monitoring over months, try to give samples at the same time of day each time, ideally at the same laboratory.
TSH, T3, T4 के लिए उपवास आवश्यक नहीं। हालांकि, सुबह के परीक्षण (7–10 बजे) बेहतर हैं क्योंकि TSH में हल्की दैनिक भिन्नता होती है। -
Use the same lab for serial monitoring
TSH assays can vary by 10–20% between different lab platforms. For monitoring thyroid treatment over months, always use the same laboratory — a falling TSH from 3.8 to 2.1 at the same lab is meaningful; comparing values across different labs can be misleading.
सीरियल मॉनिटरिंग के लिए हमेशा एक ही लैब का उपयोग करें। TSH परख विभिन्न लैब प्लेटफॉर्म के बीच 10–20% तक भिन्न हो सकती है।
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थायराइड की समस्याएं अक्सर विटामिन D और B12 की कमी के साथ आती हैं — सभी तीन कारण एक जैसे हैं: थकान, बालों का झड़ना, वजन की समस्याएं। यह पैकेज एक ही ड्रॉ में सब कुछ जांचता है।Related Tests / संबंधित जांचें
These tests are commonly ordered alongside or after a thyroid panel in India:
भारत में थायराइड पैनल के साथ या बाद में ये जांचें अक्सर करवाई जाती हैं:Frequently Asked Questions / अक्सर पूछे जाने वाले सवाल
The standard TSH normal range for most Indian adults is 0.4 to 4.0 mIU/L. However, this range has nuances: in pregnancy, the upper limit drops to 2.5 mIU/L in the first trimester and 3.0 in the second and third trimesters — because even mildly elevated TSH in pregnancy can affect foetal brain development. In elderly patients above 70, some clinicians accept a slightly higher upper normal of 5.0–6.0. Always check the reference range printed on your specific lab report, as assays differ between labs.
उत्तर: अधिकांश भारतीय वयस्कों के लिए TSH सामान्य सीमा 0.4–4.0 mIU/L है। गर्भावस्था में ऊपरी सीमा पहली तिमाही में 2.5 और दूसरी-तीसरी में 3.0 mIU/L तक गिर जाती है।Always give your blood sample BEFORE taking your morning thyroid medication (Thyronorm, Eltroxin, or any levothyroxine). Taking the medicine first causes a transient peak in blood T4 levels and may suppress TSH slightly — making your thyroid function appear better controlled than it actually is. After the blood draw, take your medicine as usual. Do not skip the dose — just delay it by 30–60 minutes.
उत्तर: हमेशा सुबह की थायराइड दवा लेने से पहले ब्लड सैंपल दें। दवा 30–60 मिनट देरी से लें, छोड़ें नहीं।It depends on the cause. Most hypothyroidism in India is autoimmune (Hashimoto's thyroiditis) — a chronic condition requiring lifelong daily medication (levothyroxine) rather than a cure. The medication simply replaces what the thyroid is not making — patients on the right dose feel and live completely normally. Hyperthyroidism (Graves' disease) can sometimes be permanently treated with radioactive iodine (RAI) therapy or thyroid surgery, though these may also result in permanent hypothyroidism requiring lifelong replacement. Subclinical hypothyroidism that is not autoimmune and is mild sometimes resolves on its own.
उत्तर: यह कारण पर निर्भर करता है। अधिकांश हाइपोथायरायडिज्म (Hashimoto's) आजीवन दवा की आवश्यकता है, इलाज नहीं। हाइपरथायरायडिज्म को रेडियोआयोडीन या सर्जरी से स्थायी रूप से इलाज किया जा सकता है।No — fasting is not required for TSH, T3, or T4 tests. Thyroid hormone levels are not significantly affected by food intake. Morning tests (7–10 AM) are preferred for consistency because TSH has a mild diurnal variation — slightly higher in early morning and lower in the evening. If your thyroid test is part of a panel that includes fasting blood sugar or lipid profile, follow the fasting instructions for those tests. For thyroid alone, no preparation is needed except the medication timing rule and biotin warning described above.
उत्तर: नहीं — TSH, T3, T4 के लिए उपवास आवश्यक नहीं। सुबह 7–10 बजे परीक्षण बेहतर है। दवा का समय नियम और बायोटिन चेतावनी का पालन करें।This is called subclinical hypothyroidism — the most common thyroid finding on routine Indian health checkups. Whether to treat depends on several factors. Treatment is usually recommended if: TSH is above 10 mIU/L (regardless of symptoms), you are pregnant or trying to conceive (treat even with TSH above 2.5), Anti-TPO antibodies are elevated (suggesting future progression), or you have clear symptoms. For TSH between 4–10 with normal Free T4 and no symptoms in a non-pregnant adult, a repeat test in 3–6 months and lifestyle monitoring may be appropriate before starting medication. Never make this decision alone — consult an endocrinologist.
उत्तर: यह सब-क्लिनिकल हाइपोथायरायडिज्म है। उपचार तब अनुशंसित है: TSH 10 से ऊपर, गर्भावस्था या गर्भधारण की कोशिश, उच्च Anti-TPO, या स्पष्ट लक्षण। TSH 4–10 + सामान्य FT4 + कोई लक्षण नहीं = एंडोक्रिनोलॉजिस्ट से परामर्श।Yes — significantly. Biotin (Vitamin B7) is widely consumed in India for hair fall, often in doses of 5–10 mg/day in "hair-skin-nail" supplements. High-dose biotin interferes with the immunoassay method used in most modern thyroid tests — causing falsely low TSH and falsely high T3/T4 values, mimicking hyperthyroidism. This has led to patients in India being unnecessarily investigated or even treated for hyperthyroidism they did not have. Stop all biotin-containing supplements at least 48 hours (ideally 72 hours for very high doses) before your thyroid test, and inform your doctor and lab that you take biotin.
उत्तर: हां — महत्वपूर्ण रूप से। उच्च-खुराक बायोटिन (5–10 mg/day) TSH को गलत तरीके से कम और T3/T4 को गलत तरीके से उच्च दिखाता है — हाइपरथायरायडिज्म की नकल करता है। थायराइड टेस्ट से कम से कम 48 घंटे पहले बायोटिन बंद करें।- MedlinePlus (NIH): TSH (Thyroid Stimulating Hormone) Test
- American Thyroid Association: Hypothyroidism Patient Information
- NCBI: Biotin Interference in Thyroid Assays
⚠️ Medical Disclaimer / चिकित्सा अस्वीकरण
This article is for educational and informational purposes only. It is NOT a substitute for professional medical advice. Normal thyroid ranges vary between laboratories — always refer to the reference range on your specific report. Never adjust your thyroid medication based on this guide. Always seek advice from a qualified endocrinologist or physician.
यह लेख केवल शैक्षिक उद्देश्यों के लिए है। केवल लैब रिपोर्ट या इस गाइड के आधार पर अपनी थायराइड दवा कभी न बदलें। हमेशा एक योग्य एंडोक्रिनोलॉजिस्ट या डॉक्टर से सलाह लें।
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