kensa ni ha ketueki ga hituyou desu.

• 検査 = けんさ
• に = に
• は = は
• 血液 = けつえき
• が = が
• 必要 = ひつよう
• です = です

A natural full reading is:

けんさには けつえきが ひつようです。

In this sentence, には is に + は.

• に marks the thing something is for: for / in / during / with regard to
• は adds a topic or contrast nuance

So 検査には means something like:

• for the test
• as for the test
• when it comes to the test

A very literal breakdown is:

• 検査には = for the test / as for the test
• 血液が = blood
• 必要です = is necessary

So the sentence structure is basically:

For the test, blood is necessary.

Because は can attach to other particles, including に, to create a topic or contrast.

So:

• 検査に血液が必要です = Blood is necessary for the test.
• 検査には血液が必要です = As for the test, blood is necessary. / For the test, blood is necessary.

Using には often gives one of these feelings:

1. Topic-setting: speaking about the test...
2. Contrast/emphasis: for the test, blood is needed (maybe not for something else)

So には is very common and natural here.

Because 必要です does not work like a normal action verb such as 飲む or 食べる.

With 必要, the thing that is needed is usually marked by が:

• お金が必要です。 = Money is necessary.
• 時間が必要です。 = Time is necessary.
• 血液が必要です。 = Blood is necessary.

So in this pattern:

A には B が 必要です
= B is necessary for A

Here:

• 検査には = for the test
• 血液が = blood
• 必要です = is necessary

English uses need very differently, so learners often expect を, but Japanese grammar here uses が.

必要 is usually treated as a na-adjective in grammar explanations, though it also has noun-like behavior.

That is why it can appear like this:

• 必要です = is necessary
• 必要なもの = a necessary thing
• 必要ではありません = is not necessary

In this sentence, 必要です means is necessary / is needed.

So 血液が必要です literally means:

Blood is necessary.

Not:

Someone needs blood.

Even though English often translates it with need.

Grammatically, the sentence does not say who needs it.

It simply says:

For the test, blood is necessary.

In natural English, we might say:

• The test requires blood.
• A blood sample is needed for the test.
• Blood is necessary for the test.

Japanese often leaves out the person or organization if it is obvious from context. So this sentence focuses on the requirement itself, not on the person doing the needing.

It could use 要る, but 必要です is very common and slightly more formal or neutral.

Compare:

• 検査には血液が必要です。
  = Blood is necessary for the test.
• 検査には血液が要ります。
  = The test needs blood. / Blood is needed for the test.

Both can work, but 必要です often sounds a bit more formal, written, or explanatory, which fits medical or official contexts well.

By itself, 検査 can mean:

• inspection
• examination
• test
• checkup

But because the sentence says 血液が必要です, the context strongly suggests a medical test/exam.

So here, learners should understand 検査 as something like:

• medical test
• examination
• procedure

Context determines the exact English wording.

Japanese often uses a broader or more direct noun where English prefers a more specific phrase.

So:

• 血液が必要です literally = Blood is necessary
• natural English may be = A blood sample is needed

In a medical setting, Japanese does not always spell out sample if the meaning is obvious. So 血液 here can naturally imply the blood that will be collected for testing.

Yes, 血 means blood, and 血液 also means blood, but there is a nuance difference.

• 血 is shorter and more everyday
• 血液 is more technical, clinical, or formal

In a medical or hospital context, 血液 sounds especially appropriate. So in this sentence, 血液 fits the tone very well.

The standard order here is:

検査には血液が必要です。

This is natural and clear.

Because Japanese is flexible, some reordering is possible, but the original order is the most straightforward. It presents:

1. the context/purpose: 検査には
2. the thing needed: 血液が
3. the judgment: 必要です

That makes it easy to process.

A very useful pattern is:

A には B が 必要です
= B is necessary for A

Examples:

• 旅行にはお金が必要です。
  = Money is necessary for travel.
• 勉強には時間が必要です。
  = Time is necessary for studying.
• 検査には血液が必要です。
  = Blood is necessary for the test.

This is a very common pattern, so it is worth memorizing.

必要です is polite, standard Japanese.

Related forms:

• 必要だ = plain form
• 必要です = polite form
• 必要ではありません = is not necessary
• 必要ですか = is it necessary?

So the sentence is in a normal polite style, which is very appropriate in medical explanations, instructions, or general conversation.

A very literal breakdown is:

検査には = for the test / as for the test
血液が = blood
必要です = is necessary

So the literal structure is:

For the test, blood is necessary.

This literal view helps explain why the particles are what they are, even if the best English translation might be something smoother like A blood sample is needed for the test.