O hematócrito está normal, então começamos.

O is the masculine singular definite article, meaning the.

In Portuguese, nouns normally take an article much more often than they do in English. So o hematócrito is simply the hematocrit or the hematocrit level/result.

Why masculine? Because hematócrito is a masculine noun, so it takes o, not a.

Because estar is usually used for a current state or condition, while ser is used for something more permanent, defining, or general.

Here, o hematócrito está normal means the hematocrit result is normal right now / in this situation.

Compare:

• O hematócrito está normal. = The hematocrit is normal.
• É normal. = It is normal / That is normal / It is common.

So está normal is the natural choice for a lab result or medical reading.

Because normal is an adjective that has the same form for masculine and feminine singular.

So you get:

• o hematócrito normal
• a pressão normal

Both use normal.

Only the plural changes:

• os resultados normais
• as taxas normais

So in O hematócrito está normal, normal stays exactly the same.

Here, então means something like so, then, or in that case.

It connects the two ideas:

• O hematócrito está normal
• então começamos

So the logic is: the result is normal, so we begin / proceed.

Depending on context, então can also mean:

• then in time sequence
• so in a cause-and-effect sense
• sometimes a filler word in conversation, like well or so

In this sentence, it is clearly the cause-and-effect meaning.

Because então is linking two clauses, much like English so in a sentence like The result is normal, so we start.

The comma helps separate the two parts:

• O hematócrito está normal
• então começamos

This is standard punctuation in Portuguese.

Portuguese often leaves out subject pronouns when the verb form already makes the subject clear.

Começamos already tells you the subject is we, so nós is not required.

So both are possible:

• Então começamos.
• Então nós começamos.

The version without nós is very natural and common.
Adding nós can give emphasis or make the sentence a little clearer, but it is not necessary.

Yes. This is a very important point.

Começamos can be either:

• present tense: we start / we are starting
• preterite (simple past): we started / we began

Portuguese has this same form for nós with many -ar verbs.

So the exact meaning depends on context.

Examples:

• Agora começamos. = We’re starting now.
• Ontem começamos. = We started yesterday.

In your sentence, the surrounding context determines whether it means so we begin or so we began.

The ç is there to keep the s sound before a.

Without the cedilla, c before a would sound like k. So:

• ca = usually a k sound
• ça = an s sound

The infinitive is começar. In forms before a, o, or u, Portuguese uses ç to preserve that soft sound:

• começar
• começamos
• começou

But before e or i, regular c already has the soft sound, so no cedilla is needed:

• comecei
• comece

The accents mostly tell you where the stress goes, and sometimes they also affect vowel quality.

• hematócrito → stress on tó
• está → stress on the last syllable, tá
• então → stress on tão, and ão is nasal

A rough pronunciation guide:

• hematócrito ≈ eh-ma-TOH-kree-too
• está ≈ es-TAH
• então ≈ en-TAŨ (with a nasal ending)

A few notes:

• The h in hematócrito is silent.
• The ão sound in então is very common in Portuguese and does not exist in the same way in English.
• The accent in está helps distinguish it from esta in writing.

Yes, it sounds natural.

In Brazilian Portuguese, it is very common to talk about test results or measurements this way:

• A pressão está normal.
• A glicose está alta.
• O colesterol está baixo.
• O hematócrito está normal.

This structure is very productive:

[article + medical term] + está + adjective

So the sentence sounds normal and idiomatic in a medical context.