維生素C血液檢測是測量採血當下您血液中抗壞血酸的濃度。這是您在檢驗報告上較少見到的項目之一。大多數人從未做過這項檢測，因為醫師通常能從飲食狀況和症狀判斷維生素C是否不足，不需要數值佐證。當這項檢測被開立時，通常是為了確認某位因飲食、疾病或生活方式而有缺乏風險的患者是否真的缺乏。
In this article you’ll learn what vitamin C does in the body, why this test is ordered so rarely, why the sample has to be handled with unusual care, what a low or a normal result actually tells you, who is most at risk of running short, and when a conversation with your doctor is worthwhile.
What vitamin C does, and why levels are measured
Vitamin C, also called ascorbic acid, is a water-soluble vitamin. Water-soluble simply means it dissolves in water rather than in fat, so the body cannot stockpile it the way it stores vitamin D or vitamin A. Humans are also unusual among mammals: we lack a working version of the enzyme that most animals use to build vitamin C from sugar. Every milligram we have comes from food or supplements.
That combination — no internal production, no large reserve — is exactly why a blood level can be informative. Vitamin C does several jobs that matter every day:
- It helps build collagen, the structural protein that holds skin, gums, blood vessels, bone and tendons together. This is why a shortage shows up as bleeding gums, fragile skin and slow wound healing.
- It acts as an antioxidant, meaning it neutralises unstable molecules called free radicals before they damage cells.
- It improves the absorption of non-heme iron, the form of iron found in plants. If you are following iron results, you may want to read 我們的血清鐵血液檢測指南.
- It supports the normal functioning of several immune cells.
- It helps make carnitine, a molecule that ferries fats into the parts of the cell that produce energy.
One nuance matters when you read your result. A plasma vitamin C level mostly reflects what you have eaten recently, not the size of your body’s total reserve. It is a snapshot of intake rather than a long-term memory, which is part of why doctors interpret it alongside your diet and symptoms rather than on its own.
Why and when a vitamin C blood test is ordered
Vitamin C testing is not part of a routine check-up, and it is not included in standard panels. A doctor generally orders it when something in the clinical picture points towards deficiency. Typical triggers include:
- Unexplained easy bruising, bleeding or inflamed gums, or tiny pinpoint bleeds around hair follicles.
- Wounds or surgical sites that are healing far more slowly than expected.
- Persistent fatigue and aching joints in someone with a visibly restricted diet.
- 已知的高風險情況包括：長期飲酒、飲食不足、接受透析治療、曾接受減重手術、有飲食失調問題，或患有影響吸收的疾病，例如克隆氏症或乳糜瀉。
- 無法以常見原因完全解釋的貧血。在這種情況下，您的醫師可能也會想進一步檢查 我們的全血球計數（CBC）指南.
Why the test stays uncommon
There are sound reasons why this test is rarely used. Scurvy — the severe form of vitamin C deficiency — is diagnosed mainly on history and physical examination, and it responds so quickly to treatment that the response itself confirms the diagnosis. Not every laboratory offers the assay, results can take days to come back, and the number reflects recent intake, so a single supplement taken before the appointment can mask a chronic shortage. The test is a supporting piece of evidence, not the decision-maker.
What the test is called on your lab report
The same measurement travels under several names. You may see it printed as vitamin C, ascorbic acid, plasma ascorbic acid or serum vitamin C. Results are usually reported in micromoles per litre (µmol/L) in Europe, or in milligrams per decilitre (mg/dL) in the United States. The unit is important, because the reference range only makes sense next to it. If reference ranges in general are new to you, consult 我們的血液檢測正常值參考表.
How the sample is handled, and why timing changes the result
Vitamin C is one of the most fragile substances a laboratory is ever asked to measure. Ascorbic acid oxidises — reacts with oxygen and breaks down — when exposed to light, warmth and air. A tube left sitting on a bench will quietly lose vitamin C, and the result that comes back will be lower than your true level.
正因如此，執行此項檢測的實驗室會嚴格遵守操作流程：血液須採集至冷藏試管中，通常立即置於冰浴中，迅速以離心機分離血漿，並遮光保存，且常需加入化學穩定劑，樣本在分析前須冷凍保存。操作流程中任何一個環節出現偏差，都可能導致數值偏低的假性結果。
What this means for you in practice is simple. Ask the laboratory in advance whether it actually performs this test and what preparation it wants, since instructions genuinely vary from site to site. Mention any vitamin C supplement you take and when you last took it, because a dose that morning can lift your level temporarily and hide a real shortfall. If your result looks surprising in either direction, sample handling is a legitimate thing to ask about before drawing conclusions. For the wider picture, read 我們的血液檢查報告完整解讀指南.
Reading a low vitamin C result
數值偏低表示您近期的維生素C攝取量未能滿足身體需求，這是一個營養狀態的訊號，本身並不構成診斷。實驗室會標記低於參考範圍的結果；根據2024年《Nutrition Reviews》一篇綜述所引用的國際研究標準，血漿或血清維生素C濃度低於11.4 µmol/L定義為缺乏，介於中間的數值則描述為邊緣性不足或耗竭。
缺乏症不會一夜之間出現，也不會一次全部顯現。隨著體內儲量下降，症狀會依照相當可預測的順序逐漸出現。
| 分期 | Typical timing after intake stops | What people notice |
|---|---|---|
| Reserves falling | 最初幾週 | Usually nothing at all; the blood level drops silently |
| 早期、非特異性症狀 | 約4至12週 | Tiredness, low mood, irritability, loss of appetite, aching muscles |
| 與膠原蛋白相關的症狀 | 約3個月後 | 牙齦出血或腫脹、容易瘀青、毛囊周圍出現針點狀出血、體毛捲曲如螺旋狀、傷口難以癒合 |
| 嚴重缺乏（壞血病） | Months of near-zero intake | Joint pain and swelling, anaemia, marked weakness; requires prompt medical care |
Timings are indicative and taken from published clinical reviews. They vary from person to person depending on starting reserves and overall health.
Scurvy is rare, but no longer purely historical
Scurvy is the name for advanced vitamin C deficiency. It is genuinely rare in high-income countries, and it should not be a source of alarm for most readers. It is worth knowing about for one reason only: it is reversible, and it is easy to miss precisely because doctors were taught to think of it as a disease of eighteenth-century sailors. Clinicians have been reporting scattered cases in specific groups — older adults living alone, people with severe alcohol use disorder, people facing food insecurity, and people with very restricted eating patterns.
Tests your doctor may add
維生素C偏低的情況很少單獨出現，因為缺乏維生素C的飲食通常也缺乏其他營養素。因此，醫師可能會同時檢查鐵質、葉酸、維生素B12和鈣，並可能進一步安排 我們的鋅血液檢測指南。發炎也會降低血液中的維生素C濃度，因此建議將 our article about the CRP inflammation marker 與您的檢驗結果一併參考。若對鐵質儲存量有疑慮，請參閱 our guide to low ferritin levels，而更全面的評估則可透過 我們的維生素與營養素檢測指南.
Reading a normal or high vitamin C result
結果在參考範圍內，表示您近期的攝取量已足夠。這確實是個令人放心的消息，對大多數人來說，這個問題到此就可以告一段落。不過請記住，正常值反映的是近幾天的狀況，並不代表您的組織已完全補足，這也是為什麼醫師會同時參考您的飲食習慣和症狀來解讀結果。
High levels are far less common and almost always come from supplements rather than food. It is close to impossible to reach an excessive level by eating fruit and vegetables, because absorption becomes less efficient as the dose rises and the kidneys clear the surplus into urine.
What high-dose supplements can and cannot do
The evidence here deserves a sober reading. Large doses of vitamin C do not prevent colds in the general population, and the widely repeated claim that vitamin C treats cancer is not supported by robust clinical evidence. Very high intakes carry their own drawbacks:
- 消化方面的不適是最常見的問題，包括腹瀉、腹部痙攣和噁心，通常在減少劑量後即可緩解。
- The body converts surplus vitamin C into oxalate, a compound excreted by the kidneys. In men with a history of kidney stones or existing kidney disease, high supplemental intakes have been linked to a greater risk of stones. In that setting, doctors often follow 我們的腎功能檢查指南 及 our guide to the uric acid blood test.
- Vitamin C can interfere with other laboratory tests, including some blood glucose meters and faecal occult blood tests, producing misleading results.
- It may interact with certain medicines, including anticoagulants and some chemotherapy agents.
For reference points on intake, the NIH Office of Dietary Supplements sets the recommended dietary allowance at 90 mg per day for adult men and 75 mg per day for adult women, adds 35 mg per day for people who smoke, and sets a tolerable upper intake level of 2,000 mg per day for adults. These are the figures published by that authority; the right amount for you is a conversation to have with your doctor, particularly before starting any supplement.
Who is most at risk of vitamin C deficiency
缺乏維生素C更多是環境因素造成的，而非個人意志力的問題。以下族群在臨床研究中被公認為風險較高。
| 集團 | Why risk is higher |
|---|---|
| People with limited access to fresh food | 食物取得困難及費用問題，使得定期攝取蔬果變得不易 |
| Older adults living alone | Restricted, repetitive diets and reduced shopping or cooking capacity |
| People who smoke | Higher oxidative stress consumes vitamin C faster, raising daily needs |
| Heavy alcohol use | Poorer dietary intake combined with greater losses through the kidneys |
| Malabsorption conditions | 克隆氏症、乳糜瀉和囊狀纖維化會影響腸道的吸收 |
| 接受減重手術後 | Reduced intake and reduced absorbing surface |
| People on dialysis or with a kidney transplant | Vitamin C is water-soluble and is removed during dialysis; dietary restrictions limit intake |
| People with eating disorders or highly selective eating | Narrow food range that may exclude all vitamin C sources |
| People who are seriously ill in hospital | Higher consumption during illness alongside poor intake |
烹調方式也很重要。維生素C會因加熱而分解，也會溶入烹調用水中，因此新鮮或輕度蒸煮的食物所保留的維生素C，遠多於水煮的食物。
何時應就醫
若您發現牙齦在沒有明顯牙科問題的情況下出血、輕微碰撞後就出現瘀青、腿部毛囊周圍出現細小紅點，或傷口遲遲未癒合，請盡快預約就診。
Speak to your doctor within a reasonable timeframe if you have persistent unexplained fatigue and joint aches together with a diet that has contained little fruit or vegetable for weeks, or if you belong to one of the risk groups listed above.
Seek medical care without delay for severe weakness, significant joint swelling or pain that limits walking, or any bleeding that concerns you.
Talk to your doctor before starting a high-dose vitamin C supplement, particularly if you have had kidney stones, have kidney disease, or take anticoagulant or chemotherapy medicines.
Latest scientific advances in vitamin C testing
Research published since 2023 has reshaped how specialists think about this marker. Here is what the recent work found, and what it means for you as a patient.
住院患者中維生素C缺乏比預期更為常見
2024年，Golder等人在《Nutrition Reviews》發表了一篇範疇性文獻回顧，彙整了所有符合條件的研究，探討富裕國家中成年住院患者的維生素C濃度。範疇性文獻回顧是一種系統性的文獻調查，旨在全面梳理某一議題的現有證據，而非針對單一療法進行驗證。綜合各項研究後，研究人員發現，約四分之一接受檢測的住院成年患者呈現維生素C缺乏，其中病情嚴重或原本營養狀況較差者的比例最高。退休身份以及大量飲酒和吸菸，被認定為獨立的風險因子，且維生素C缺乏與更嚴重的身體衰弱及認知困難有關。
What this means for you: deficiency is not an exotic curiosity confined to history books, and it clusters in people who are already unwell. If you or a relative are in hospital with poor appetite, asking about nutrition is a reasonable thing to do. The authors themselves caution that the studies varied a great deal in who they tested, so the figure describes hospital patients who were selected for testing rather than the general public.
The sample really is as fragile as laboratories say
Luo 等人於 2024 年在《營養與代謝年鑑》（Annals of Nutrition and Metabolism）發表的研究，採用一種稱為液相層析串聯質譜法的高精度技術（可依分子質量進行分離與鑑定），測試水溶性維生素在不同保存條件下的穩定性。抗壞血酸是受測物質中穩定性最差的之一：在室溫下會降解，即使放在一般冰箱中也會如此。在離心前將全血置於冰浴中可有效保存維生素 C，而深度冷凍則能讓樣本在數天內維持可靠的檢測結果。
What this means for you: the handling instructions attached to this test are not bureaucratic fuss, they are the difference between a true and a false result. It is entirely legitimate to ask how your sample was transported if a result looks unexpectedly low, and to ask whether repeating it is worthwhile.
Kidney patients are a genuinely at-risk group
Yepes-Calderón and colleagues published a 2024 study in the European Journal of Nutrition following several hundred kidney transplant recipients from the TransplantLines biobank. Vitamin C deficiency was common at every point after transplantation, and recipients consistently had lower levels than healthy potential donors. Diabetes and active smoking were the characteristics most strongly linked to deficiency, while higher intake from food or supplements was linked to lower odds of being deficient.
What this means for you: if you live with kidney disease or have had a transplant, vitamin C is a reasonable topic to raise with your nephrology team. This was an observational study, meaning it observed people rather than assigning treatments, so it shows an association and cannot prove that correcting the level changes outcomes.
臨床醫師被提醒重新認識一個舊有的診斷
Gandhi 等人於 2023 年在《疾病》（Diseases）期刊發表的綜述文章，題為〈壞血病：重新認識一種被遺忘的疾病〉（Scurvy: Rediscovering a Forgotten Disease），說明了為何已開發國家仍會出現零星病例，以及為何這些病例如此容易被忽略。作者描述，目前維生素 C 缺乏症主要出現在年長者、營養不良者或社會孤立者身上，甚至可能以消化道出血的形式表現。Ndukwe 等人於 2025 年在《PLOS One》發表的研究計畫書，正式提出了加拿大的相同隱憂，指出壞血病已在特定族群中重新出現，並制定了一套計畫以釐清受影響的對象及原因。計畫書所描述的是一項規劃中的研究，而非已產出結果的研究。
What this means for you: the practical value of these papers is that they prompt clinicians to consider a diagnosis that treats easily once recognised. If your symptoms fit and your circumstances fit, mentioning your diet explicitly to your doctor genuinely helps.
詞彙表
| 術語 | 定義 |
|---|---|
| 抗壞血酸 | The chemical name for vitamin C, and the name most often printed on lab reports |
| 水溶性 | 溶於水而非脂肪，因此不會大量儲存於體內，多餘的部分會隨尿液排出 |
| 血漿 | The liquid part of blood left once the cells are spun out; where vitamin C is measured |
| 膠原蛋白 | 皮膚、牙齦、血管及骨骼的結構蛋白，若缺乏維生素C，身體便無法正常合成 |
| 抗氧化劑 | 一種能中和自由基的物質；自由基是會損傷細胞的不穩定分子 |
| Scurvy | The clinical illness caused by severe, prolonged vitamin C deficiency; reversible with treatment |
| Oxidation | 與氧氣發生的化學反應，會使維生素 C 分解，無論是在食物中還是在血液樣本中皆然 |
| 分析前階段 | 從抽血到分析之間的所有環節，脆弱的檢測指標最容易在這個過程中流失 |
| 草酸鹽 | 一種由身體利用多餘的維生素 C 合成的化合物，經腎臟排出，並與某些腎結石的形成有關 |
| 參考範圍 | The span of values found in most healthy people tested by that laboratory, used as a comparison point |
常見問題
Is there actually a blood test for vitamin C?
Yes. Laboratories can measure ascorbic acid in plasma or serum, and specialist laboratories can also measure it inside white blood cells, which reflects longer-term stores more faithfully than plasma does. The plasma test is the one usually offered. It is simply not routine: it is not part of standard panels, not every laboratory runs it, and doctors reach for it only when the clinical picture suggests deficiency.
抽血前可以補充維生素 C 嗎？
若是專門進行維生素 C 檢測，事先服用補充劑可能使您的數值在數小時內偏高，從而掩蓋真正的缺乏狀況，因此請告知您的醫師或檢驗室您所服用的補充劑及服用時間。維生素 C 也可能干擾其他不相關的檢測，包括某些血糖儀及糞便潛血檢查。最安全的做法是不要自行停用任何補充劑，而是主動告知檢驗室或醫師，由他們給予建議。
做維生素 C 血液檢查前需要空腹嗎？
Requirements vary between laboratories, and some do ask for a morning sample after an overnight fast so that the reading is not skewed by a recent meal or drink. Because vitamin C levels move with what you have just eaten, timing matters more here than for many other markers. Always follow the instructions given by the laboratory performing your test, and call them in advance if none were provided.
What is the vitamin C blood test called on a lab form?
Look for vitamin C, ascorbic acid, plasma ascorbic acid or serum vitamin C. They all refer to the same measurement. You may also see leukocyte ascorbic acid, which is a different and less widely available test that measures vitamin C inside white blood cells and reflects your reserves rather than your recent intake.
How much does a vitamin C blood test cost?
費用完全取決於您所在的國家、您的檢驗室，以及此項檢查是否有醫療適應症。若由醫師開立以評估疑似缺乏症，通常與其他處方檢查一樣有健保給付或相應補助。若無醫療適應症而自費送驗，由於所需設備與處理程序較為複雜，費用通常比一般常規檢查高，屬於專項檢測的收費標準。您可直接向檢驗室詢問確切費用。
檢測結果正常，是否仍可能缺乏維生素C？
It can, in one specific situation. Because plasma reflects recent intake, someone who has eaten well for a couple of days before the test, or taken a supplement, may show a normal level while their tissue stores are still low. This is why doctors weigh the number against your symptoms and your usual diet rather than treating it as the final word, and why a result that does not match how you feel is worth discussing.
參考資料
- 美國國立衛生研究院膳食補充劑辦公室 — 維生素C：醫療專業人員資訊表 — https://ods.od.nih.gov/factsheets/VitaminC-HealthProfessional/
- MedlinePlus, U.S. National Library of Medicine — Scurvy: Medical Encyclopedia — https://medlineplus.gov/ency/article/000355.htm
- Maxfield L, Daley SF, Crane JS — Vitamin C Deficiency — StatPearls, NCBI Bookshelf, National Library of Medicine, 2023 — https://www.ncbi.nlm.nih.gov/books/NBK493187/
- Golder JE, Bauer JD, Barker LA, Lemoh CN, Gibson SJ, Davidson ZE — Prevalence, risk factors, and clinical outcomes of vitamin C deficiency in adult hospitalized patients in high-income countries: a scoping review — Nutrition Reviews, 2024 — https://doi.org/10.1093/nutrit/nuad157
- Luo W, Wang D, Tang Y, Cheng Q, Ma X, Yu S, Qiu L — Water-Soluble Vitamins Stability by Robust Liquid Chromatography-Mass Spectrometry — Annals of Nutrition and Metabolism, 2024 — https://doi.org/10.1159/000541587
- Yepes-Calderón M, van der Veen Y, Martín Del Campo S F, Kremer D, Sotomayor CG, Knobbe TJ, Vos MJ, Corpeleijn E, de Borst MH, Bakker SJL — Vitamin C deficiency after kidney transplantation: a cohort and cross-sectional study of the TransplantLines biobank — European Journal of Nutrition, 2024 — https://doi.org/10.1007/s00394-024-03426-7
- Gandhi M et al. — Scurvy: Rediscovering a Forgotten Disease — Diseases, 2023 — https://consensus.app/papers/details/3ac4b68ba7c55deb90e1a349d2622ae7/
- Ndukwe C et al. — Shining light on vitamin C deficiency and scurvy in Canada: A scoping review protocol of risk profiles, health outcomes, and interventions — PLOS One, 2025 — https://consensus.app/papers/details/27c0da4b370d5fc6a0b241998a64fd39/
延伸閱讀
- To continue with the other vitamins measured in blood, read 我們關於維生素D血液檢查的指南.
- For the marker most often paired with folate, consult our guide to the vitamin B12 blood test.
- To understand a closely related B vitamin, see our guide to the folic acid blood test.
- For another antioxidant vitamin measured in blood, browse 我們的維生素E血液檢測指南.
- To put any flagged value in context, read 我們的血液檢測異常結果指南.
用 AI DiagMe 讀懂您的檢驗報告
維生素C的檢測結果很少單獨解讀，通常需要搭配鐵質、全血球計數（CBC）或C反應蛋白（CRP）一起判讀。當這些數值交織在一起，報告往往就開始讓人看不懂。AI DiagMe能將您的檢驗報告轉化為淺顯易懂的說明，讓您在就診時能提出更有針對性的問題，而不是帶著滿腹疑慮前往。它幫助您了解自己的檢驗結果，但不提供診斷，也無法取代您的醫師。
