Bilo da je dao krv bilo da nije, zavoj je potreban.

It means whether ... or ....

So:

• Bilo da je dao krv, bilo da nije = Whether he gave blood or not
• zavoj je potreban = a bandage is necessary

This pattern is used to show that the result is the same in both cases.

A very literal breakdown is something like:

• bilo da X, bilo da Y = whether X or Y

In everyday English, you would usually translate this sentence naturally as:

• Whether he gave blood or not, a bandage is needed.

Yes, it comes from biti (to be), but in this construction bilo da functions as a fixed conjunction-like expression.

So even though bilo is historically the neuter past form of biti, in bilo da ... bilo da ... you should usually learn it as a whole pattern meaning:

• whether ... or ...

In other words, here it is not really acting like an ordinary past-tense verb that you need to analyze separately every time.

Because Serbian often uses the full pattern on both sides:

• bilo da je dao krv, bilo da nije

This is a balanced, formal, and very natural way to say whether he gave blood or not.

In English, we usually do not repeat whether:

• whether he gave blood or not

But Serbian often likes the parallel structure:

• bilo da ..., bilo da ...

You may also encounter shorter alternatives in Serbian, depending on style, such as:

• Bilo da je dao krv ili ne, zavoj je potreban.

That means essentially the same thing.

Because je dao is the standard perfect tense in Serbian.

It is made of:

• the auxiliary je (has/is, from biti)
• the past participle dao (given)

So:

• je dao krv = he gave / he has given blood

Serbian often uses this perfect tense where English simply uses the past.

Because Serbian often omits words that are already understood from context.

So:

• bilo da je dao krv, bilo da nije

really means:

• bilo da je dao krv, bilo da nije dao krv

The verb phrase is left out in the second part because it would be repetitive.

This kind of omission is very common and natural.

Here nije means he did not / he hasn’t, with the rest understood from the previous clause.

More literally:

• nije = is not / has not

But in this sentence, because it refers back to je dao krv, it is understood as:

• nije dao krv = he didn’t give blood

So in context:

• bilo da je dao krv, bilo da nije = whether he gave blood or not

Because Serbian often leaves subject pronouns out when they are clear from the verb form or context.

So instead of saying:

• bilo da je on dao krv

Serbian naturally says:

• bilo da je dao krv

The meaning he is understood.

This is very common in Serbian and is one of the biggest differences from English.

Because dao is from the perfective verb dati (to give), and here the sentence refers to a completed act:

• Did he give blood or not?

That is a single completed event, so perfective aspect fits naturally.

Compare:

• dao = gave / has given once, as a completed act
• davao = was giving / used to give / gave repeatedly

In this sentence, davao would sound wrong because the point is not repeated or ongoing giving, but whether the event happened.

It is in the accusative case, because it is the direct object of dao.

• dao šta? = what did he give?
• krv = blood

For this noun, the accusative looks the same as the nominative:

• nominative: krv
• accusative: krv

So even though the form does not change, the case is still accusative because of its role in the sentence.

Literally, it means:

• bandage is necessary

More natural English:

• a bandage is needed
• a bandage is necessary

Breakdown:

• zavoj = bandage
• je = is
• potreban = necessary / needed

So potreban agrees with zavoj.

Because potreban must agree with zavoj in gender, number, and case.

• zavoj is masculine singular
• so the adjective is potreban

Compare:

• zavoj je potreban = masculine singular
• krv je potrebna = feminine singular
• pismo je potrebno = neuter singular
• zavoji su potrebni = masculine plural

This is standard adjective agreement.

Both are possible.

• Zavoj je potreban
• Potreban je zavoj

They mean basically the same thing, but the emphasis can differ slightly.

• Zavoj je potreban puts zavoj first as the topic.
• Potreban je zavoj can sound a bit more like what is needed is a bandage.

In your sentence, zavoj je potreban is a very natural neutral order.

Because the opening part is a subordinate clause:

• Bilo da je dao krv bilo da nije = Whether he gave blood or not

Then comes the main clause:

• zavoj je potreban = a bandage is needed

So the comma separates the introductory clause from the main statement.

You will also often see a comma inside the bilo da ... bilo da ... pair for clarity:

• Bilo da je dao krv, bilo da nije, zavoj je potreban.

That punctuation is often even clearer.

It sounds correct and fairly neutral, but the bilo da ... bilo da ... structure can feel a bit more formal or carefully written than the simplest everyday phrasing.

In conversation, many speakers might also say:

• Ako je dao krv ili nije, zavoj je potreban.
• Bez obzira na to da li je dao krv ili ne, zavoj je potreban.
• Bilo da je dao krv ili ne, zavoj je potreban.

The original sentence is perfectly good Serbian, especially in written or slightly formal contexts.

Yes, depending on context.

Literally, dao krv means gave blood. But in real-life usage, that can refer to:

• donated blood
• had blood drawn
• gave blood in a medical context generally

So the best English translation depends on the situation already known from context.

If the context is blood donation, then:

• Whether he donated blood or not, a bandage is needed.

If the context is a blood draw at a clinic, then:

• Whether blood was taken from him or not, a bandage is needed

might fit better, though that would no longer be a word-for-word translation.

It can be followed by different verb forms, depending on meaning.

For example:

• Bilo da dođe, bilo da ne dođe, počećemo.
  Whether he comes or not, we’ll start.

• Bilo da je došao, bilo da nije, to ništa ne menja.
  Whether he came or not, that changes nothing.

So bilo da is flexible. In your sentence, the perfect tense je dao is used because it refers to whether a past action happened.