Deze patiënt is allergisch.

Yes. Deze means this when used with a de-word singular noun, or with a plural noun.

• deze patiënt = this patient
• die patiënt = that patient

A useful overview:

• deze = this / these
• die = that / those

More specifically:

• singular de-word: deze
• singular het-word: dit
• plurals: deze

Since patiënt is a de-word, deze is correct.

It is a de-word: de patiënt.

So you get:

• de patiënt
• deze patiënt
• die patiënt

This matters because demonstratives and some adjectives depend on whether a noun is a de or het word.

Because deze already functions as the determiner.

In English, you also say:

• this patient not
• this the patient

Dutch works the same way:

• deze patiënt = correct
• deze de patiënt = incorrect

Dutch main clauses usually follow the verb-second rule.

In this sentence:

• Deze patiënt = first element
• is = finite verb, in second position
• allergisch = rest of the sentence

So the pattern is:

subject + verb + complement

That is very similar to English here:

• This patient is allergic.

Because allergisch is being used as a predicative adjective: it comes after is and describes the subject.

In Dutch, predicative adjectives usually do not take the extra -e ending.

Compare:

• De patiënt is allergisch.
  The patient is allergic.

But before a noun, the adjective usually does take -e:

• de allergische patiënt
  the allergic patient

So:

• after is → allergisch
• before a noun → often allergische

Yes, but it means something slightly different in structure.

• Deze patiënt is allergisch. = This patient is allergic.
• Deze patiënt heeft een allergie. = This patient has an allergy.

Both can be natural, but they are not identical word-for-word:

• is allergisch describes a condition or characteristic
• heeft een allergie names the thing the patient has

In many contexts, is allergisch is the most direct match for English is allergic.

Yes, it can absolutely stand on its own.

• Deze patiënt is allergisch. = This patient is allergic.

If you want to specify the allergen, Dutch often uses voor:

• Deze patiënt is allergisch voor penicilline.
• Deze patiënt is allergisch voor noten.

So the short sentence is complete, even without saying what the allergy is.

The accent in patiënt shows that the vowels are pronounced separately rather than blending into one syllable.

Roughly, it sounds like:

• pa-ti-ENT

The final part -iënt is pronounced in separate syllables, not as a simple English-style ending.

The dieresis-like mark is not used here; instead, Dutch writes an acute accent in patiënt as part of the standard spelling of this loanword. For a learner, the key point is:

• it is a normal, correctly spelled Dutch word
• you should keep the accent when writing it

Roughly, it sounds like:

• ah-ler-khiss

A few points for English speakers:

• g in Dutch is usually not a hard English g as in go
• it is often a throaty sound, especially in standard northern Dutch
• the ending -isch sounds something like -ieskh or -iskh, not like English -ic

You do not need a perfect accent right away, but be careful not to pronounce it exactly like English allergic.

Yes. That would mean:

• That patient is allergic.

So the difference is just:

• deze patiënt = this patient
• die patiënt = that patient

Both are completely normal.

In this specific sentence, Dutch and English are actually very similar.

• Deze patiënt = This patient
• is = is
• allergisch = allergic

So the structure is basically the same:

subject + be + adjective

Dutch differs more noticeably from English in other sentence types, especially with adverbs, subordinate clauses, and separable verbs. But this sentence is fairly straightforward.

Yes.

For example:

• Hij is allergisch. = He is allergic.
• Zij is allergisch. = She is allergic.
• Die is allergisch. = That one is allergic. / That person is allergic.

In a medical context, deze patiënt is often used because it is explicit and formal.

It is neutral and fits especially well in a medical or clinical context.

Because patiënt is a medical word, the sentence sounds natural in:

• hospital notes
• medical discussions
• training material
• formal explanations

It is not especially informal, but it is not unnatural or overly stiff either.

Normally, only the first word of the sentence is capitalized:

• Deze patiënt is allergisch.

So:

• Deze is capitalized because it starts the sentence
• patiënt and allergisch are not capitalized

Dutch does not capitalize ordinary nouns the way German does.

The plural would be:

• Deze patiënten zijn allergisch.
  These patients are allergic.

Changes:

• patiënt → patiënten
• is → zijn
• deze stays deze for plural

So deze can mean both this and these, depending on the noun.