Você está apto, contanto que o hematócrito esteja normal.

Because você takes third-person singular verb forms in Portuguese, even though it means you.

So:

• você está = you are
• você é = you are

This is one of the first things English speakers have to get used to in Portuguese:

• tu estás = you are using tu
• você está = you are using você

In most of Brazil, você is very common in everyday speech.

Estar is used because this sentence is talking about a current condition or status, not a permanent characteristic.

• estar apto = to be fit / eligible / cleared at this moment
• ser apto would sound more like an inherent quality or general ability, and is much less natural here

In medical, legal, or administrative contexts, estar apto is very common:

• Ele está apto para trabalhar.
• Você está apto para doar sangue.

So here, você está apto means something like you are fit / eligible / cleared, depending on context.

Here, apto means fit, eligible, qualified, or cleared, depending on the situation.

It is often used in formal or semi-formal contexts such as:

• medicine
• employment
• exams
• legal/administrative procedures

So Você está apto does not usually mean you are skilled in the everyday sense. It means more like:

• you meet the requirements
• you are medically fit
• you are allowed to proceed

Because contanto que normally requires the subjunctive.

So:

• contanto que ... esteja = provided that ... is
• not contanto que ... está

The subjunctive is used here because the clause expresses a condition, something that must be true for the main statement to apply.

This pattern is very common:

• Contanto que ele venha...
• Desde que tudo esteja certo...
• A menos que chova...

So in your sentence:

• Você está apto, contanto que o hematócrito esteja normal. = You are fit/eligible, provided that the hematocrit is normal.

Contanto que means provided that, as long as, or on condition that.

It is correct and natural, but it sounds a bit more formal or careful than some everyday alternatives.

Other similar expressions are:

• desde que = as long as / provided that
• se = if

Examples:

• Você pode ir, contanto que volte cedo.
• Você pode ir, desde que volte cedo.

Both are good, but contanto que often feels a little more explicit about a condition.

Yes. In many contexts, desde que would work very well and sound natural.

For example:

• Você está apto, desde que o hematócrito esteja normal.

That has almost the same meaning as the original sentence.

A small nuance:

• contanto que can sound a bit more formal or emphatic about the condition
• desde que is often more common in everyday Brazilian Portuguese

Both usually take the subjunctive, so you would still say esteja, not está.

The comma separates the main clause from the conditional subordinate clause.

Main clause:

• Você está apto

Condition:

• contanto que o hematócrito esteja normal

In writing, that comma is very natural and helps readability. You may sometimes see punctuation vary depending on style, but in this sentence the comma is standard and appropriate.

Yes. Apto agrees with the person it describes.

Forms:

• apto = masculine singular
• apta = feminine singular
• aptos = masculine plural
• aptas = feminine plural

So:

• to a man: Você está apto
• to a woman: Você está apta

This is an important agreement point in Portuguese adjectives.

Normal is an adjective describing o hematócrito, which is masculine singular.

In the singular, normal has the same form for masculine and feminine:

• o hematócrito normal
• a taxa normal

In the plural, it changes:

• normais

So:

• o hematócrito esteja normal
• os valores estejam normais

Hematócrito is a masculine singular noun:

• o hematócrito

That is why the sentence has:

• o hematócrito
• esteja for a singular subject
• normal for a singular adjective

It is a technical medical term, so the whole sentence sounds fairly formal or clinical.

The stress falls on tó:

• he-ma-TÓ-cri-to

A rough English-friendly approximation is:

• eh-mah-TOH-kree-too

And the full phrase:

• o hematócrito esteja normal

If you want a more careful pronunciation guide:

• hematócrito: /emaˈtɔkɾitu/ in Brazilian Portuguese, with natural regional variation

The accented ó shows where the stress goes.

Yes, especially in a medical, lab, or administrative context.

That said, it sounds somewhat formal because of words like:

• apto
• contanto que
• hematócrito

A more conversational sentence might use simpler wording, depending on context. But the original sentence is completely natural if, for example, a doctor, lab worker, or official is explaining a requirement.

Usually it refers to a specific present evaluation.

Because it uses:

• você está apto = you are currently fit/eligible
• contanto que ... esteja normal = provided that ... is normal

So it sounds like someone is saying:

• You qualify right now, if that lab value is normal or
• You are cleared, provided that the hematocrit is normal

It is not mainly describing your permanent nature; it is about a condition that must be met.