У мене болить нирка.

Because this is the normal Ukrainian pattern for talking about pain in a body part.

Literally, У мене болить нирка is something like At me, the kidney hurts or I have a hurting kidney.

Ukrainian usually does not say this with я as the subject. Instead, it uses:

• у мене = at me / in me / I have
• the body part as the grammatical subject
• болить = hurts / aches

This is the same pattern as:

• У мене болить голова. = My head hurts.
• У мене болить рука. = My arm hurts.

So even though English says I in I have a pain, Ukrainian normally uses у мене.

Мене here is in the genitive case.

That is because the preposition у (or в) often requires the genitive when it means at or in the possession of in expressions like this.

So:

• я = nominative
• мене = genitive/accusative form, but here specifically understood as genitive after у

In this sentence, у мене functions as an idiomatic phrase meaning I have / with me / in my case.

Because нирка is the grammatical subject of the verb болить.

In Ukrainian, the thing that hurts is usually the subject:

• нирка болить = the kidney hurts
• голова болить = the head hurts
• спина болить = the back hurts

So in У мене болить нирка:

• у мене = marks whose kidney it is
• нирка = the thing that hurts, so it stays in the nominative
• болить agrees with нирка

Because нирка is singular.

The verb agrees with the noun that is hurting:

• У мене болить нирка. = My kidney hurts.
• У мене болять нирки. = My kidneys hurt.

So:

• singular noun → болить
• plural noun → болять

This is a very common pattern in Ukrainian.

The dictionary form is боліти.

Болить is the 3rd person singular present tense form:

• боліти = to hurt / to ache
• болить = hurts / aches
• болять = hurt / ache for plural subjects

In this sentence, you use болить because нирка is singular.

It most directly means My kidney hurts.

In natural English, depending on context, you could also translate it as:

• I have a pain in my kidney
• I have kidney pain

But the Ukrainian sentence focuses on the specific body part: the kidney hurts.

Also, because нирка is singular, it usually suggests one kidney rather than both.

Yes, grammatically you can, but it is usually less natural in ordinary speech unless you want emphasis.

• У мене болить нирка. = the normal, everyday way to say it
• Моя нирка болить. = My kidney hurts, with stronger focus on my kidney

Using моя can sound more emphatic, contrastive, or context-dependent, as if you are comparing it with something else.

For a learner, У мене болить нирка is the safest and most natural default.

Yes. У мене and в мене are both common and mean the same thing here.

The choice between у and в is often made for ease of pronunciation and smooth sound. Ukrainian frequently alternates them to avoid awkward sound combinations.

So both are fine:

• У мене болить нирка.
• В мене болить нирка.

You will hear both in real life.

Нирка means kidney.

It is a feminine noun. You can tell this from the typical feminine ending -а in the singular nominative form.

That is why other words agreeing with it would also be feminine, for example:

• ліва нирка = left kidney
• моя нирка = my kidney

No, Ukrainian word order is fairly flexible.

The neutral, natural version is:

• У мене болить нирка.

But other orders are possible for emphasis:

• Нирка у мене болить.
• Болить у мене нирка.

These alternatives change the focus or sound more marked in context, but the basic meaning stays the same.

For learners, the standard order У мене болить нирка is best to use first.

You would say:

• У мене болять нирки.

Changes:

• нирка → нирки for plural
• болить → болять to match the plural subject

So the pattern is:

• У мене болить нирка. = My kidney hurts.
• У мене болять нирки. = My kidneys hurt.

Yes, normally it is.

У мене болить нирка sounds like someone is describing physical pain in the kidney area or referring to a kidney problem.

It is not usually metaphorical. It would normally be understood as a health-related statement.

If you wanted to sound more medically precise, the exact wording might change depending on context, but this sentence is a normal everyday way to describe the symptom.

A practical pronunciation guide is:

U meNE boLYT' NYRka

A few useful notes:

• у мене = stress on -не
• болить = stress on the last syllable
• нирка = stress on the first syllable

Very rough English-style approximation:

oo meh-NEH boh-LYT NYR-kah

This is only an approximation, but it can help you get started.